| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Departments of Medicine and Physiology and Biophysics, Mayo Clinic, Rochester, Minnesota 55905
 |
ABSTRACT |
|---|
 TOP
 ABSTRACT
 INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
We
investigated the role of prostaglandins in the renal vascular response
to exogenous and endogenous adenosine in control and streptozotocin
(STZ) diabetic rats. Exogenous adenosine (0.01-100 nmol) injected
into the abdominal aorta decreased renal blood flow (RBF) in a
dose-dependent manner to a much greater extent in STZ rats than in
control rats (P < 0.001). Inhibition
of prostaglandin synthesis with indomethacin (Indo; 10 mg/kg iv) potentiated the adenosine-induced renal vasoconstriction in
control rats but not in STZ rats. In control rats, Indo shifted the
dose response curve of exogenous adenosine-induced RBF reductions to
the left by a factor of 10 (ED50:
from 5.5 ± 0.51 to 0.55 ± 0.07 nmol adenosine, n = 6, P < 0.001) and in STZ rats only by a
factor of two (ED50: from 0.32 ± 0.03 to 0.16 ± 0.02 nmol adenosine,
n = 6, P > 0.05). The renal response to
endogenous adenosine was assessed by the magnitude of the postocclusive
reduction of RBF (POR), an adenosine-mediated phenomenon. POR was
greater in STZ rats (
65.3 ± 5.2%,
P < 0.001) compared with control
rats (36.2 ± 3.5%). Indo markedly enhanced POR in control
rats (20.3 ± 3.7%) but not in STZ rats (4.5 ± 2.7%). Renal cortical and medullary
PGE2 microdialysate concentrations and urinary PGE2 excretions were
clearly not lower in STZ (cortex: 169 ± 61 pg/ml; medulla: 640 ± 88 pg/ml, urine: 138 ± 25 pg/min) compared with
control rats (cortex: 99 ± 12 pg/ml; medulla: 489 ± 107 pg/ml;
urine: 82 ± 28 pg/min). Indo significantly decreased renal
cortical, medullary, and urinary excretion of
PGE2 in STZ and control rats.
These findings demonstrate that the adenosine-induced renal
vasoconstriction is increased in the presence of Indo in control rats
but not in STZ rats. The observations suggest that the diabetic renal
vasculature may have a diminished vasodilatory capacity in response to
prostaglandins to counteract adenosine-induced renal vasoconstriction.
renal hemodynamics; experimental insulin-dependent diabetes mellitus; indomethacin; diabetic dysfunctional vasoregulation; renal ischemia
| |
INTRODUCTION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
THE RENAL VASCULAR RESPONSE to adenosine is unique in that adenosine induces vasoconstriction of the afferent glomerular arteriole via adenosine A1 receptors (19, 22), in contrast to other vascular beds in which adenosine acts as a vasodilator. A number of factors and conditions modify the renal vasoconstrictor response to adenosine, including sodium intake, renal arterial perfusion pressure, ureteral obstruction, nitric oxide, prostaglandins, and diabetes mellitus (19, 21, 22). In a previous study, we demonstrated an increased vasoconstrictive sensitivity of the renal vasculature to endogenous and exogenous adenosine in streptozotocin (STZ)-induced diabetic rats (22). The effects of adenosine on the renal vasculature in that study were mediated via adenosine A1 receptors because they were inhibited in a dose-dependent manner by the selective adenosine A1- receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (22).
Prostaglandins modulate renal function, including tubular transport and vascular hemodynamics (6). Vasodilatory prostaglandins, such as PGE2 and PGI2, regulate pre- and postglomerular tone, antagonizing renal vasoconstriction (9).
In diabetic patients and animals with experimental diabetes mellitus, several studies report alterations of renal prostaglandin synthesis (3, 13, 16, 24, 27). Both increases (3, 8, 24, 27) and decreases (13, 16) of vasodilating prostaglandin synthesis have been reported in the diabetic kidney. The diabetic renal vasculature is characterized by dysfunction of its vasodilator capacity (5, 7, 14). There is considerable evidence indicating that the extrarenal (18) and renal (14) endothelial-dependent vasodilation mediated by prostaglandins is impaired in humans and animals with diabetes mellitus, but the overall role of prostaglandin-dependent renal vasodilation in diabetes remains controversial.
Therefore, in the present study, we determined the sensitivity of the renal vasculature to adenosine during inhibition of prostaglandin synthesis and the generation of renal PGE2 in STZ-induced diabetes mellitus.
| |
MATERIAL AND METHODS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
The renal vascular response to adenosine on renal blood flow (RBF) was studied during the inhibition of prostaglandin synthesis by indomethacin (Indo) in nondiabetic control and STZ-diabetic rats. The response to exogenous adenosine was determined by injecting adenosine via a catheter placed into the abdominal aorta, which reduced RBF in a dose-dependent manner. The vascular response to endogenous adenosine was assessed by quantification of the postocclusive reduction of RBF (POR), a phenomenon shown to be mediated by adenosine A1 receptors (22).
Animal Preparation
To provide physiological conditions in nonstressed animals, experiments were performed in nonfasted male Sprague-Dawley rats; the animals had free access to a regular rat pellet diet and tap water until the morning of the experiments. The rats were anesthetized with thiopental intraperitoneally (Trapanal; Byk-Gulden) with a dose of 100 mg/kg. The animals were placed on a heated table to maintain body temperature at 37°C via a servo-controlled rectal thermometer. Respiration was spontaneous through an endotracheal tube. Two catheters were inserted into the right jugular vein. One catheter served for continuous infusion of isotonic saline (0.9 g/dl) at a rate of 2 ml/h, the other catheter served for vehicle or drug administration with a continuous infusion of isotonic saline (0.9 g/dl) at a rate of 1 ml/h. A polyethylene catheter was advanced through the left carotid artery into the abdominal aorta. This aortic catheter was made out of a PE-350, which was heated over a flame and extended to a final outside diameter of 0.8-1.0 mm. The tip of the catheter was positioned 2-3 mm above the renal artery and connected to a microinjection device for manually time-controlled (0.3-0.5 s) 30-µl bolus injection of adenosine. Care was exercised in maintaining the tip of the catheter precisely at its position. In previous experiments, the authors have shown (unpublished data) that by positioning the tip of the catheter 2-3 mm above the renal artery, the highest effective dose of adenosine administered by this technique effectively enters the renal microcirculation. Positioning the tip of the catheter further above or closer to the renal artery branch showed a lesser effect of the adenosine-induced reduction of RBF. Arterial blood pressure was continuously monitored via a right femoral artery catheter connected to a Statham pressure transducer. The heart rate was derived from the pressure tracing connected to a thermoprinter (WK-280 R; Foehr Medical Instruments). The left kidney was exposed by a subcostal flank incision and placed in a Lucite holder. After careful preparation of the kidney hilus, a flow probe was fitted around the renal artery and connected to an electromagnetic flowmeter (model 501; Carolina Medical Electronics) for continuous monitoring of RBF. Calibration of zero flow was confirmed by occluding the renal artery distal to the flow probe. The abdominal cavity was covered by a sheet of Parafilm (Laboratory Film, American National Can) to prevent evaporation of fluid. Urine from the left kidney was collected via a ureteral catheter, and the bladder was cannulated for free drainage of urine from the right kidney. The rats were allowed to stabilize after the surgical procedure for 60 min.Experimental Insulin-Dependent Diabetes Mellitus
The animal model of insulin-dependent diabetes mellitus (IDDM) was achieved by an intraperitoneal injection of 50 mg/kg STZ (Sigma) dissolved in sodium citrate buffer (pH 4.2). Tail blood samples taken 3 days after STZ injection and on the day of the experiment provided measurements of blood glucose levels. Animals with a blood glucose <250 mg/dl were not included in the experimental series. The experiments started 6-8 wk after STZ administration, and nondiabetic rats served as controls. The 50-mg/kg STZ model of IDDM was chosen to reduce malnourishment, catabolic state, weight loss, and hyperphagia, because the administered dose of STZ does not completely destroy all beta islet cells of the rat pancreas (28) and a remaining small basal insulin production is achieved with this IDDM model. Furthermore, moderate hyperglycemia was stable until the day of the experiment (blood glucose levels 3 days after STZ, 319 ± 12 mg/dl; on the day of the experiment, 346 ± 27 mg/dl).The progression of diabetic nephropathy is attributed basically to hyperglycemia and insulin deficiency (15); hence, the diabetic model of the current study without insulin treatment may represent a more progressive state of the development of diabetic nephropathy than comparable models with insulin treatment. Consequently, the presented findings may be restricted to STZ-induced diabetes mellitus without insulin treatment.
Exogenous Adenosine
Exogenous adenosine (Serva), dissolved in 0.90 g/dl NaCl, was given in sequentially increasing doses, starting from 0.01 nmol and increasing to 100 nmol, with 3-5 min between doses. Adenosine was administered via the aortic catheter in a bolus of 30 µl over 0.3-0.5 s. Adenosine bolus injections (0.01 up to 10 nmol) did not affect arterial blood pressure; higher doses (30-100 nmol) of adenosine bolus injections slightly decreased arterial blood pressure, however, only after the RBF response was almost complete. Vehicle bolus injections with isotonic saline did not result in any change of RBF. The reduction of RBF (
RBF) due to adenosine injections was assessed
as the difference of minimal postinjection RBF
(RBFmin) to baseline RBF
(RBFbaseline) as a percentage of the preinjection RBF (=
RBFbaseline)
|
(1) |
RBF%) in response to adenosine
injections (0.01-100 nmol) was plotted in graphs as dose response
curves. RBF measurements were performed by means of an electromagnetic
flowmeter fitted around the left renal artery in a pulsatile fashion,
because RBF changes occurred within the time range of a tenth of a
second. These RBF changes cannot be observed when the pulsatile
recordings are dampened. In the pulsatile RBF measurement, RBF pulse
curves interfere with the precise measurement of very small RBF
reductions. The pulsatile amplitude of the basal RBF tracing usually
ranges from 17 to 20% of basal RBF; hence, the minimal precise
detectable RBF reduction with the pulsatile RBF registration should be
>17-20% RBF. Under conditions in which the minimal dose of
adenosine (e.g., 0.01 nmol) did not reach the minimal
detectable RBF reduction (at least 20%), the dose response curve was
extrapolated to calculate the
ED50.
Endogenous Adenosine
The renal response to endogenous adenosine was assessed by the POR as described previously (22). In brief, POR was determined by release of two to three occlusions (30 s) of the renal artery. During renal artery occlusion, renal adenosine generation increases by hydrolysis of ATP (21). After release of the renal artery occlusion, the accumulated adenosine causes vasoconstriction of the afferent arterioles via adenosine A1-receptor stimulation, which is apparent in the POR after the occlusion (Fig. 1) (21, 22). As shown previously (22), the POR after release of a renal artery clamp is mediated by adenosine A1 receptor stimulation and can be inhibited in a dose-dependent manner with the highly selective adenosine A1-receptor antagonist DPCPX (22). The extent of the POR was determined via the ratio of minimal RBF after the occlusion to basal RBF as expressed in equation 1 (see Fig. 1). A recovery period of 8-10 min followed each occlusion.
|
Microdialysis Experiments of the Renal Cortex and Medulla
In vivo microdialysis studies were performed to determine intrarenal PGE2 synthesis as described by Baranowski and Westenfelder (2). Briefly, control rats and STZ rats were anesthetized with 100 mg/kg ip Inactin (thiobutabarbitol; Byk Gulden) and body temperature was maintained at 37°C via a heated table. The trachea, right jugular vein, left carotid, and the bladder were cannulated. The left kidney was exposed and immobilized by a left flank incision. Via the Seldinger technique, a small channel was made in the renal cortex and medulla with a 30-gauge needle connected to a polyethylene tubing (PE-10). Thereafter, linear microdialysis probes with 0.5-mm diameter and a 5-mm membrane (Bionalytical Systems) were inserted through the tubing in cortex and medulla, and the tubing was removed. Both probes, cortical and medullary, were then perfused at a rate of 3 µl/min with PBS containing (in mmol/l) 8 Na2HPO4, 137 NaCl, 1.5 KH2PO4, 3 KCl, 1 CaCl2, and 0.5 MgCl2. At this perfusion rate, in vitro recovery was 45% for PGE2. During a 1.5-h equilibration period, the animal received an intravenous infusion of 2.0% inulin in 0.9% NaCl at a rate of 1 ml · h
1 · 100 g body wt1 while
microdialysis probes were continuously perfused at a rate of 3 µl/min. After the equilibration period, dialysate fluid was collected
in two 40-min intervals for a total of an 80-min control measurement
period. Thereafter, Indo (10 mg/kg) dissolved in 1 ml of alkaline
saline (pH 8) was intravenously infused over 10 min, and the dialysate
was collected from the two subsequent 40-min periods. Urine was
collected via a bladder catheter. The dialysate and urine samples were
stored at 30°C until
PGE2 analysis was performed.
Experimental Protocol
The RBF experiments were started after the 60-min recovery period after surgery. The renal response to exogenous adenosine was assessed with intra-aortic single injections of adenosine, and thereafter (10 min) the renal response to endogenous adenosine was determined with the POR. The renal responses to exogenous and endogenous adenosine were assessed during vehicle infusion and after Indo infusion; between each experimental period, an equilibration period of 20 min was allowed for stabilization (see Fig. 2). At the end of the experiment, the animals were killed by an overdose of thiopental and the left kidney was removed and weighed.
|
Experimental Groups
Group 1: Effect of Indo on the renal vascular response to adenosine in control rats. The renal response to exogenous and endogenous adenosine was assessed under control conditions with an isotonic normal saline vehicle (n = 6). Thereafter, Indo (10 mg/kg) dissolved in 1 ml of alkaline saline (pH 8) was intravenously infused over 10 min and then the renal response to exogenous and endogenous adenosine was determined (see Fig. 2).Group 2: Effect of Indo on the renal vascular response to adenosine in STZ rats. The protocol of this group was identical to group 1, but in STZ rats (n = 6).
Group 3: Effect of alkaline saline vehicle of Indo on the renal vascular response to adenosine in control rats. This group (n = 5) served as the time vehicle control for group 1. The renal response to exogenous and endogenous adenosine was assessed with an isotonic normal saline vehicle. Then 1 ml of alkaline saline (pH 8) was intravenously infused over 15 min, and the renal response to exogenous and endogenous adenosine was determined.
Group 4: Effect of alkaline saline vehicle of Indo on the renal vascular response to adenosine in STZ rats. The protocol of this group was identical to group 3, but in STZ rats (n = 5).
Group 5: PGE2
in the renal cortex, medullary dialysate, and urinary
PGE2 excretion in nondiabetic
control rats. PGE2
was measured in the dialysate of the renal cortex and medulla during
control conditions (0.9% NaCl, 1 ml · h1 · 100 g body weight1 iv) and
after intravenous infusion of Indo (10 mg/kg;
n = 5).
Group 6: PGE2 in the renal cortex, medullary dialysate, and urinary PGE2 excretion in STZ-diabetic rats. The protocol of this group was identical to group 5, but in STZ rats (n = 5).
Analytic Methods
Blood glucose levels were measured with a blood glucose meter (One Touch, Lifescan) 3 days after STZ injection and on the day of the experiment after the equilibration period. Glomerular filtration rate (GFR) was calculated on the basis of the clearance of inulin. Inulin in plasma and urine was measured by the Anthrone method (11). Sodium concentrations in plasma and urine were measured by using a flame photometer (IL943 Flame Photometer, Instrumentation Laboratory). Renal interstitial fluid PGE2 levels in the dialysate samples and urinary PGE2 levels were measured by an enzymatic immunoassay (Cayman Chemical, Ann Arbor, MI).Statistical Analysis
Data were expressed as means ± SE. Two-factor ANOVA, with repeated measures on one and unpaired Student's t-test, were performed as appropriate. Statistical analysis of the ED50 values was performed by the Tukey-Kramer multiple comparisons test. P < 0.05 was considered significant.| |
RESULTS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Exogenous Adenosine
There were no significant differences between control, STZ, and time-vehicle control rats with respect to baseline values for mean arterial blood pressure, heart rate, RBF, and hematocrit (see Tables 1 and 2). In STZ-diabetic rats, the adenosine-induced reduction of RBF was markedly potentiated compared with control rats. One nanomole adenosine injected into the abdominal aorta decreased RBF by68.1 ± 6.0% in
STZ rats and by 24 ± 1.2% in control rats (see Fig.
3, A and
B). The calculated
ED50 of adenosine was
significantly greater (P < 0.001) in
control rats (5.5 ± 0.51 nmol) compared with STZ rats (0.32 ± 0.03 nmol). Hence, the dose response curve of RBF reduction by single
injections of adenosine was shifted to the left by a factor of 20 in
STZ rats compared with the dose response curve of control rats.
|
|
|
Effects of Indo on the adenosine-induced renal vasoconstriction. The ED50 of adenosine was 5.5 ± 0.51 nmol in control rats with the vehicle and 0.55 ± 0.07 nmol adenosine with Indo. This presents a significant (P < 0.001) left shift of the dose response curve of control rats with Indo by a factor of 10. In STZ rats, however, Indo shifted the dose response curve to the left only by a factor of two, which was not significant (from ED50 of 0.32 ± 0.03 nmol adenosine to ED50 of 0.16 ± 0.02 nmol adenosine, P > 0.05). Hence, the effects of Indo to increase the responsiveness to the adenosine-induced renal vasoconstriction were attenuated in STZ rats (Fig. 3, A and B). The ED50 of control rats with Indo (0.55 ± 0.07 nmol adenosine) was similar to the ED50 of STZ rats with the vehicle (0.32 ± 0.03 nmol adenosine) and not significantly different (P > 0.05).
Endogenous Adenosine
Effects of Indo on the POR. The renal vascular response to endogenous adenosine, assessed by POR, was significantly enhanced (P < 0.01) in STZ rats compared with control rats (Figs. 2 and 4). Indo increased the baseline POR by 56% in control rats but did not change baseline POR in STZ rats (see Table 1).
|
Time and Vehicle Controls
There was no time-dependent effect on the POR in control and STZ rats. The vehicle of Indo in control (group 3) and STZ (group 4) rats did not affect mean arterial blood pressure (control rats, 98.5 ± 4.2 mmHg; STZ, 92.8 ± 5.8 mmHg), heart rate (control rats, 360 ± 10.2 beats/min; STZ, 363 ± 8.7 beats/min), and RBF (control rats, 4.5 ± 0.2 ml/min; STZ, 4.3 ± 0.2 ml/min). The results demonstrate that the potentiation of the renal response to adenosine with Indo in control and STZ rats was unrelated to time- and vehicle-dependent effects.Renal Cortical, Medullary, and Urinary PGE2
The PGE2 data of the dialysate were not corrected for recovery. PGE2 dialysate concentrations of the cortex and medulla and urinary PGE2 excretion tended to be higher in STZ rats (cortex: 169 ± 61 pg/ml; medulla: 640 ± 88 pg/ml; urine: 138 ± 25 pg/min) compared with control rats (cortex: 99 ± 12 pg/ml; medulla: 489 ± 107 pg/ml; urine: 82 ± 28 pg/min). The differences of PGE2 concentrations and excretions between STZ and control were not statistically significant. PGE2 dialysate concentrations of the medulla were significantly higher compared with the cortex in both groups, STZ and control rats. Indo (10 mg/kg) decreased dialysate PGE2 concentrations in the cortex and medulla and urinary PGE2 excretion in both groups, STZ (cortex: 8 ± 2 pg/ml; medulla: 14 ± 3 pg/ml; urine: 30 ± 5 pg/min) and control rats (cortex: 17 ± 1 pg/ml; medulla: 30 ± 7 pg/ml; urine: 20 ± 2 pg/min; see Fig. 5).
|
In control rats, Indo infusion did not significantly change mean arterial pressure (vehicle: 126 ± 9 mmHg; Indo: 122 ± 8 mmHg), GFR (vehicle: 2.9 ± 0.1 ml/min; Indo: 3.2 ± 0.3 ml/min), urine flow (vehicle: 32 ± 9 ml/h; Indo: 53 ± 19 ml/min), and fractional sodium (vehicle: 0.8 ± 0.4%; Indo: 1.8 ± 1.4%). In STZ rats, Indo infusion did not significantly change mean arterial pressure (vehicle: 129 ± 4 mmHg; Indo: 123 ± 4 mmHg), GFR (vehicle: 2.4 ± 0.4 ml/min; Indo: 2.0 ± 0.4 ml/min), urine flow (vehicle: 31 ± 5 ml/h; Indo: 17 ± 2 ml/min), and fractional sodium (vehicle: 0.6 ± 0.1%; Indo: 0.5 ± 0.1%).
| |
DISCUSSION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Enhanced adenosine-induced renal vasoconstriction in STZ-diabetic rats. The present findings show that the adenosine-induced renal vasoconstriction was markedly enhanced in STZ rats compared with control rats. Adenosine (1 nmol) injected into the abdominal aorta caused a markedly greater reduction of RBF in STZ rats compared with control rats. Because intrarenal adenosine generation may cause a different renal vascular response than single injections of adenosine, the generation of endogenous adenosine was assessed by a 30-s renal artery occlusion. This resembles a more continuous adenosine generation, and again there was a markedly greater reduction and duration of RBF in STZ rats compared with control rats. During renal ischemia, e.g., renal artery occlusion, adenosine generation is increased by hydrolysis of ATP to adenosine throughout the kidney (21, 22). The accumulated renal adenosine stimulates A1 receptors on the afferent arteriole and causes renal vasoconstriction as manifested in the POR (22). The diabetic kidney has been shown to have a much higher susceptibility to ischemic periods, e.g., renal artery occlusion, which eventually may lead to diabetic nephropathy (20, 22). Hence, an increased sensitivity to adenosine-induced renal vasoconstriction may be one of the pathophysiological mechanisms responsible for the higher susceptibility of the diabetic kidney to ischemia. Because the POR is an adenosine A1 receptor-mediated phenomenon (22), increased adenosine A1 receptor density could potentially contribute to the increased sensitivity of the diabetic renal vasculature to adenosine. However, adenosine A1 receptor density was not increased in glomeruli of STZ rats compared with control rats (1), thus other factors, including a diminished prostaglandin-dependent vasodilator capacity of the diabetic renal vasculature to counteract the renal vasoconstrictor action of adenosine, may account for the increased sensitivity of the diabetic kidney to adenosine. We, therefore, investigated the RBF response to adenosine in the presence of prostaglandin synthesis inhibition in control and STZ-diabetic rats.
Attenuated Effect of Inhibition of Prostaglandin Synthesis (Indo) on the Adenosine-Induced Renal Vasoconstriction in STZ-Diabetic Rats
In the present studies, the inhibition of prostaglandin synthesis by Indo markedly potentiates the adenosine-induced renal vasoconstriction in control rats but not in STZ-diabetic rats. Indo increased the POR in control rats after a 30-s renal artery occlusion, suggesting that during renal ischemia vasodilating prostaglandins counteract the endogenous adenosine-induced renal vasoconstriction.The RBF reduction by single injections of adenosine was markedly enhanced in the presence of Indo in control rats, indicated by a left shift of the dose response curve by factor 10. This suggests that prostaglandins also counterbalance the vasoconstrictive effects of exogenous adenosine in control rats. Similar findings have been observed with ANG II (26). In these studies, cyclooxygenase inhibition significantly increased the duration of the renal vasoconstrictor response to intravenous boluses of ANG II and potentiated the renal pressor response to ANG II. Likewise, in humans, aspirin increased the renal vasoconstriction of ANG II (31).
The ED50 of control rats with Indo was similar to the ED50 of STZ rats with vehicle, thus the adenosine-induced renal vasoconstriction in STZ rats with vehicle can be mimicked in control rats with Indo. In contrast to control rats, in STZ rats Indo did not change the adenosine-induced renal vasoconstriction. Adenosine injected into the lower abdominal aorta caused a 20% RBF reduction, and Indo did not further increase the adenosine-induced renal vasoconstriction in STZ rats (Fig. 3B), whereas in control rats, Indo increased the adenosine-induced RBF reduction (Fig. 3A). This suggests that the prostaglandin-dependent vasodilator capacity of the afferent arteriole is diminished or dysfunctional in the diabetic renal vasculature. A diminished or dysfunctional prostaglandin-dependent renal vasodilation of the afferent arterioles in STZ-diabetic rats could account for the increased sensitivity of the diabetic renal vasculature to the vasoconstrictor potency of adenosine and the attenuated effects of prostaglandin inhibition on the adenosine-induced renal vasoconstriction in STZ rats.
Dysfunction of the Prostaglandin-Dependent Vasodilation in the Diabetic Renal Vasculature
In the current study, 6-8 wk after STZ injection, renal PGE2 levels in the cortex, medulla, and urine were not decreased in the two groups, STZ and control rats. In both groups, PGE2 was significantly higher in the renal medulla than in the cortex, indicating its major site of production under normal conditions (30). These findings demonstrate that a prostaglandin deficiency is unlikely to be responsible for the attenuated effects of prostaglandin synthesis inhibition in STZ rats. In addition, other studies also have found that PGE2 synthesis is not decreased in the diabetic kidney, e.g., in incubated isolated glomeruli from STZ rats 2-3 wk after STZ treatment (3, 24, 27) and in urine of patients with diabetes mellitus (12). However, others have reported decreased generation of renal vasodilating prostaglandins in diabetes mellitus (13, 16). Alterations of renal prostaglandin synthesis in diabetes can probably be in part attributed to the experimental diabetes mellitus model. Renal prostaglandin synthesis in experimental diabetes mellitus likely depends on the duration and on the presence of insulin, because insulin treatment (23) and glucose (17) increased PGE2 synthesis in STZ rats.The present findings suggest that generation of renal vasodilating prostaglandins is not diminished in STZ rats and that the responsiveness of the renal vasculature to inhibition of prostaglandin synthesis is attenuated in STZ rats. This suggests that the vascular smooth muscle may be insensitive to vasodilating prostaglandins in diabetic rats. Several factors within the prostaglandin signal transduction pathway could be responsible for a diminished vasodilation of the diabetic vascular smooth muscle cell, including decreased release of cAMP or a defective coupling of the receptor to its effector (29). Furthermore, prostaglandin-dependent renal vasodilation was found to interact with nitric oxide-dependent renal vasodilation (7), which is diminished in diabetes mellitus. Hence, a reduced prostaglandin vasodilating capacity may be linked to a diminished nitric oxide-dependent vasodilation in diabetes. Thus, even though prostaglandin synthesis is not diminished in STZ rats, prostaglandin-dependent renal vasodilation may be diminished or uncoupled from the vascular smooth muscle.
In summary, the present findings show that the diabetic renal vasculature has an increased sensitivity to the adenosine-induced renal vasoconstriction. The adenosine-induced renal vasoconstriction is increased by inhibition of prostaglandin synthesis in control rats but not in diabetic STZ rats. The observations suggest that the diabetic renal vasculature has a diminished vasodilator capacity in response to prostaglandins to counteract adenosine-induced renal vasoconstriction.
Perspectives
The present observations are of clinical relevance because adenosine has been proposed as a pathophysiological factor in the development of acute renal failure induced by contrast media (4). Contrast media-induced acute renal failure has a higher incidence in diabetic patients with impaired renal function (25). In these situations, renal adenosine is thought to be released during renal ischemic conditions with subsequent effects on the vascular and tubular system of the kidney. Therefore, a defective prostaglandin-dependent renal vasodilation may contribute to an increased adenosine-induced renal vasoconstriction as a pathophysiological factor in contrast media-induced renal failure in diabetes mellitus. Adenosine receptor antagonists may be beneficial in these settings (10).| |
ACKNOWLEDGEMENTS |
|---|
The authors gratefully acknowledge the contributions of Klaus Stieler, Dr. Hartmut Osswald, and Carla Ramsey and Joanne Zimmerman for secretarial assistance. The authors gratefully acknowledge the support of Merav Malka.
| |
FOOTNOTES |
|---|
Part of this study served as the doctoral dissertation of A. C. Pflueger and was awarded with the Medical Dissertation Award of Professor Diertrich Plester-Stiftung by the Faculty of Medicine of the Eberhard-Karls University of Tuebingen on October 23, 1997.
The study was supported by the research grant award of the Alfred Teufel Stiftung of Freunde der Universitaet Tuebingen, by National Institute of Diabetes and Digestive and Kidney Diseases Grant DK-19715, and by the Mayo Foundation.
Part of this study was presented at the 6th International Symposium on Adenosine, Ferrara, Italy, in May 1998.
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: A. C. Pflueger, Departments of Medicine and Physiology, Mayo Clinic, Guggenheim 9, Rochester, MN 55905 (E-mail: pflueger.axel{at}mayo.edu).
Received 18 February 1999; accepted in final form 2 July 1999.
| |
REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
MATERIAL AND METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Albinus, M.,
S. Halene,
R. Riehle,
R. Englert,
and
H. Osswald.
Characterization of adenosine-A1-receptors in glomerular membranes from rats with streptozotocin-induced diabetes mellitus (Abstract).
Naunyn Schmiedebergs Arch. Pharmacol.
349:
114,
1994.
2.
Baranowski, R.,
and
C. Westenfelder.
Estimation of renal interstitial adenosine and purine metabolites by microdialysis.
Am. J. Physiol.
267 (Renal Fluid Electrolyte Physiol. 36):
F174-F182,
1994
3.
Barnett, R.,
L. Scharschmidt,
Y. H. Ko,
and
D. Schlondorff.
Comparison of glomerular and mesangial prostaglandin synthesis and glomerular contraction in two rat models of diabetes mellitus.
Diabetes
36:
1468-1475,
1987[Abstract].
4.
Bohle, A.,
J. Christensen,
F. Kobot,
H. Osswald,
H. Schubert,
H. Kendziora,
H. Pressler,
and
J. Marcovic Lipovski.
Acute renal failure in man: new aspects concerning pathogenesis.
Am. J. Nephrol.
10:
374-388,
1990[Medline].
5.
Carmines, P. K.,
K. Ohishi,
and
H. Ikenaga.
Functional impairment of renal afferent arteriolar voltage-gated calcium channels in rats with diabetes mellitus.
J. Clin. Invest.
98:
2564-2571,
1996[Medline].
6.
Conrad, K. P.,
and
M. J. Dunn.
Renal prostaglandins and other eicosanoids.
In: Renal Physiology, edited by E. E. Windhager. New York: Oxford University Press, 1992, p. 1707-1757.
7.
Dai, R. X.,
A. Diederich,
J. Skopec,
and
D. Diederich.
Diabetes-induced dysfunction in streptozotocin-treated rats: role of prostaglandin endoperoxides and free radicals.
J. Am. Soc. Nephrol.
4:
1327-1336,
1993[Abstract].
8.
Dunlop, M. E.,
E. Muggli,
and
S. Clark.
Differential disposition of lysophosphatidylcholine in diabetes compared with raised glucose: implications for prostaglandin production in the diabetic kidney glomerulus in vivo.
Biochim. Biophys. Acta
1345:
306-316,
1997[Medline].
9.
Edwards, R.
Effects of prostaglandins on vasoconstrictor action in isolated renal arterioles.
Am. J. Physiol.
248 (Renal Fluid Electrolyte Physiol. 17):
F779-F784,
1985
10.
Erley, C. M.,
S. H. Duda,
S. Schlepckow,
J. Koehler,
P. E. Huppert,
W. L. Strohmaier,
A. Bohle,
T. Risler,
and
H. Osswald.
Adenosine antagonist theophylline prevents the reduction of glomerular filtration rate after contrast media application.
Kidney Int.
45:
1425-1431,
1994[Medline].
11.
Fuehr, J.,
J. Kaczmarczyk,
and
C. Kruettgen.
Eine einfache colorimetrische Methode zur Inulinbestimmung fuer Nieren Clearance Untersuchungen bei Stoffwechselgesunden und Diabetikern.
Klin. Wochenschr.
33:
729-730,
1955[Medline].
12.
Gambardella, S.,
D. Andreani,
A. Cancelli,
U. Di Mario,
I. Cardamone,
G. Stirati,
G. A. Cinotti,
and
F. Pugliese.
Renal hemodynamics and urinary excretion of 6-keto-prostaglandin F1 alpha and thromboxane B2 in newly diagnosed type I diabetic patients.
Diabetes
37:
1044-1048,
1988[Abstract].
13.
Harrison, H. E.,
A. H. Reece,
and
M. Johnson.
Effect of insulin treatment on prostacyclin in experimental diabetes.
Diabetologia
18:
65-68,
1980[Medline].
14.
Hayashi, K.,
M. Epstein,
R. Loutzenhiser,
and
H. Forster.
Impaired myogenic responsiveness of the afferent arteriole in streptozotocin-induced diabetic rats: role of eicosanoid derangements.
J. Am. Soc. Nephrol.
2:
1578-1586,
1992[Abstract].
15.
Hostetter, T. H.,
J. L. Troy,
and
B. M. Brenner.
Glomerular hemodynamics in experimental diabetes mellitus.
Kidney Int.
19:
410-415,
1981[Medline].
16.
Hoult, J. R. S.,
and
P. K. Moore.
Prostaglandin synthesis and inactivation in kidneys and lungs of rats with experimental diabetes.
Clin. Sci. (Colch.)
59:
63-66,
1980[Medline].
17.
Koya, D.,
M. R. Jirousek,
Y. W. Lin,
H. Ishii,
K. Kuboki,
and
G. L. King.
Characterization of protein kinase C beta isoform activation on the gene expression of transforming growth factor-beta, extracellular matrix components, and prostanoids in the glomeruli of diabetic rats.
J. Clin. Invest.
100:
115-126,
1997[Medline].
18.
Mayhan, W. G.,
L. K. Simmons,
and
G. M. Sharpe.
Mechanism of impaired responses of cerebral arterioles during diabetes mellitus.
Am. J. Physiol.
260 (Heart Circ. Physiol. 29):
H319-H326,
1991
19.
McCoy, D. E.,
S. Bhattacharya,
B. A. Olson,
D. G. Levier,
L. J. Arend,
and
W. S. Spielman.
The renal adenosine system: structure, function and regulation.
Semin. Nephrol.
13:
31-40,
1993[Medline].
20.
Melin, J.,
O. Hellberg,
L. M. Akyuerek,
O. Kaellskog,
and
E. Larsson.
Ischemia causes rapidly progressive nephropathy in the diabetic rat.
Kidney Int.
52:
985-991,
1997[Medline].
21.
Osswald, H.
Adenosine and renal function.
In: Regulatory Function of Adenosine, edited by R. M. Berne,
T. W. Rall,
and R. Rubio. London: Martinus Nijhof, 1983.
22.
Pflueger, A. C.,
F. Schenk,
and
H. Osswald.
Increased sensitivity of the diabetic renal vasculature to adenosine in streptozotocin-induced diabetes mellitus rats.
Am. J. Physiol.
269 (Renal Fluid Electrolyte Physiol. 38):
F529-F535,
1995
23.
Quilley, J.,
and
J. C. McGiff.
Influence of insulin on urinary eicosanoid excretion in rats with experimental diabetes mellitus.
J. Pharmacol. Exp. Ther.
238:
606-611,
1986
24.
Ramsammy, L. S.,
B. Haynes,
C. Josepovitz,
and
G. J. Kaloyanides.
Mechanism of decreased arachidonic acid in the renal cortex of rats with diabetes mellitus.
Lipids
28:
433-439,
1993[Medline].
25.
Rudnick, M. R.,
S. Goldfarb,
L. Wexler,
A. Ludbrook,
M. J. Murphy,
E. F. Halpern,
J. A. Hill,
M. Winnford,
M. B. Cohen,
and
D. B. VanFossen.
Nephrotoxicity of ionic contrast media in 1196 patients: a randomized trial.
Kidney Int.
47:
254-261,
1995[Medline].
26.
Satoh, S.,
and
B. G. Zimmerman.
Influence of the renin-angiotensin system on the effect of prostaglandin synthesis inhibitors in the renal vasculature.
Circ. Res.
37:
89-96,
1975.
27.
Schambelan, M.,
S. Blake,
J. Strear,
M. Bens,
M.-P. Nivez,
and
F. Wahbe.
Increased prostaglandin production by glomeruli isolated from rats with streptozotocin-induced diabetes mellitus.
J. Clin. Invest.
75:
404-412,
1985.
28.
Shafrir, E.
Diabetes in animals.
In: Ellenberg & Rifkins's Diabetes Mellitus (5th ed.), edited by D. Porte, Jr.,
and R. S. Sherwin. Stamford, CT: Appleton & Lange, 1997, p. 301-348.
29.
Silbiger, S. R.,
A. J. Cohen,
J. B. Fishman,
and
J. S. Stoff.
Defective glomerular beta-adrenergic signal transmission in spontaneously diabetic rats.
J. Lab. Clin. Med.
124:
249-254,
1994[Medline].
30.
Siragy, H.,
M. Ibrahim,
A. Jaffa,
R. Mayfield,
and
H. Margolius.
Rat renal interstitial bradykinin, prostaglandin E2, and cyclic guanosine 3',5'-monophosphate.
Hypertension
23:
1068-1070,
1994
31.
Uberti, M.,
S. Federico,
G. DiMinno,
B. Ungaro,
G. Ardillo,
C. Pecoraro,
B. Cianciaruso,
A. M. Cerbone,
F. Cirillo,
M. Pannain,
A. Gargiulo,
and
V. E. Andreucci.
Effects of angiotensin II on plasma ADH, prostaglandin synthesis, and water excretion in normal humans.
Am. J. Physiol.
248 (Renal Fluid Electrolyte Physiol. 17):
F254-F259,
1985.
This article has been cited by other articles:
|
|
 |
|
  V. Vallon, B. Muhlbauer, and H. Osswald Adenosine and kidney function. Physiol Rev, July 1, 2006; 86(3): 901 - 940. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 P. B. Hansen and J. Schnermann Vasoconstrictor and vasodilator effects of adenosine in the kidney Am J Physiol Renal Physiol, October 1, 2003; 285(4): F590 - F599. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 Y.-F. Chen, P.-L. Li, and A.-P. Zou Oxidative stress enhances the production and actions of adenosine in the kidney Am J Physiol Regulatory Integrative Comp Physiol, December 1, 2001; 281(6): R1808 - R1816. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. B. Persson Tubuloglomerular feedback in adenosine A1 receptor-deficient mice Am J Physiol Regulatory Integrative Comp Physiol, November 1, 2001; 281(5): R1361 - R1361. [Full Text] [PDF]
|
|
|
|
 |
|
 S. T. Davidge Prostaglandin H Synthase and Vascular Function Circ. Res., October 12, 2001; 89(8): 650 - 660. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. P. Silldorff and T. L. Pallone Adenosine signaling in outer medullary descending vasa recta Am J Physiol Regulatory Integrative Comp Physiol, March 1, 2001; 280(3): R854 - R861. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
