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Am J Physiol Regul Integr Comp Physiol 279: R484-R491, 2000;
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Vol. 279, Issue 2, R484-R491, August 2000

Cardiovascular actions of centrally and peripherally administered trout urotensin-I in the trout

Nagi Mimassi1, Fatemeh Shahbazi2, Jörgen Jensen2, Dominique Mabin1, J. Michael Conlon3, and Jean-Claude Le Mével1

1 Laboratoire de Neurophysiologie (LATIM EA 2218), Unité de Formation et de Recherche de Médecine, Université de Bretagne Occidentale, 29285 Brest Cedex, France; 2 Zoological Institute, Department of Zoophysiology, Göteborg University, SE 40530 Göteborg, Sweden; and 3 Regulatory Peptide Center, Department of Biomedical Sciences, Creighton University Medical School, Omaha, Nebraska, 68178


    ABSTRACT
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

The cardiovascular effects of centrally and peripherally administered synthetic trout urotensin (U)-I, a member of the corticotropin-releasing hormone family of neuroendocrine peptides, were investigated in unanesthetized rainbow trout Oncorhynchus mykiss. Intracerebroventricular injections of U-I (5.0 and 12.5 pmol) produced a sustained increase in mean dorsal aortic blood pressure (PDA) without significant change in heart rate (HR). This elevation in PDA was associated with an increase in cardiac output, but systemic vascular resistance did not change. Intra-arterial injection of U-I (12.5-500 pmol) evoked a dose-dependent increase in PDA, but in contrast to the hemodynamic effects of centrally administered U-I, the hypertensive effect was associated with an increase in systemic vascular resistance and an initial fall in cardiac output. HR did not change or underwent a delayed increase. Pretreatment of trout with prazosin, an alpha -adrenoreceptor antagonist, completely abolished the rise in arterial blood pressure after intra-arterial administration of U-I, which was replaced by a sustained hypotension and tachycardia. Trout U-I produced a dose-dependent (pD2 = 7.74 ± 0.08) relaxation of preconstricted rings of isolated trout arterial vascular smooth muscle, suggesting that the primary action of the peptide in the periphery is vasorelaxation that is rapidly reversed by release of catecholamines. Our results suggest that U-I may regulate blood pressure in trout by acting centrally as a neurotransmitter and/or neuromodulator and peripherally as a neurohormone functioning either as a locally acting vasodilator or as a potent secretagogue of catecholamines.

arterial blood pressure; heart rate; cardiac output; catecholamines; isolated vessels; teleost


    INTRODUCTION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

MORPHOLOGICAL AND HISTOLOGICAL studies have established that the caudal portion of the spinal cord of jawed fishes includes a neurosecretory system. In teleosts, columns of linearly arranged neuronal cell bodies, located in the caudal spinal cord, project axons into a well-defined and highly vascularized organ, the urophysis (3, 5, 14). The urophysis is a major site of synthesis of two bioactive peptides: urotensin (U)-I and -II. U-I was first isolated in pure form from an extract of the urophysis of the white sucker Catostomus commersoni and subsequently from the carp Cyprinus carpio, the flathead sole Hippoglossides elassodon, and the flounder Platichytes flesus and from the caudal spinal cord of an elasmobranch, the spotted dogfish Scyliorhinus canicula (reviewed in Ref. 29). More recently, the primary structure of U-I from the rainbow trout Oncorhynchus mykiss was deduced from nucleotide sequence of the cDNA (2). U-I shows limited structural similarity to mammalian corticotropin-releasing hormone (CRH), the frog skin peptide sauvagine, and diuretic peptides from a range of insect species (21). It has been shown that the central nervous system of Catostomus expresses a gene encoding a CRH peptide that differs in structure from rat CRH by only two amino acid residues so that U-I cannot simply be regarded as the piscine equivalent of mammalian CRH (15, 23). Interest in the U-I family of peptides has been stimulated by the identification of a cDNA encoding a U-I-related peptide, termed urocortin, in a rat midbrain cDNA library (28) and the cloning of the urocortin gene from a human genomic library (6). Compared with the other fish orthologs, trout U-I has the closest sequence identity to the mammalian urocortins (21).

The cardiovascular actions of the urotensins are markedly species dependent (5). Infusions or bolus injections of Catostomus U-I in the dog produce hypotension that is due to a selective vasodilatation of the mesenteric vascular bed that could not be prevented by adrenergic, histaminergic, or muscarinic blocking agents (22). Catostomus U-I also produced prolonged hypotension in the rat and human, but vasodilation was less regionally specific (14). In vitro, U-I potently relaxed helical strips of smooth muscle from the rat mesenteric artery (25). Chromatographically pure Catostomus U-I produced dose-dependent vasodepressor responses of relatively short duration in Columiform and Galliform birds (30). In contrast, in an elasmobranch, the spotted dogfish Scyliorhinus canicula, bolus intra-arterial injections of dogfish U-I produced a weak and transient initial vasodilator response followed by a strong and sustained pressor response that was mediated, at least in part, by release of catecholamines (27). Surprisingly, the cardiovascular properties of U-I peptides in teleosts have not been studied extensively. A partially purified preparation of U-I from Catostomus exerted prolonged vasopressor effects in the eel Anguilla rostrata as well as increasing urine flow and urinary Ca2+ and Mg2+ concentrations (4). In the flounder Platichthys flesus, infusion of flounder U-I had no effect on blood pressure (13).

In a previous study, we analyzed the hemodynamic effects of trout U-II in the conscious trout Oncorhynchus mykiss (18). The aim of the present study was to use the same experimental model to investigate the central and peripheral cardiovascular effects of synthetic trout U-I.


    MATERIALS AND METHODS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Chemicals. Trout U-I was synthesized and purified as previously described (27). Norepinephrine and prazosin hydrochloride were obtained from Sigma Chemical (Saint-Quentin Fallavier, France). U-I was stored at -70°C in stock solution (Ringer solution + 0.1% bovine serum albumin). All agents were diluted to the desired concentration with Ringer solution (vehicle) just before use. The composition of the Ringer solution was (in mM) 124 NaCl, 3 KCl, 0.75 CaCl2, 1.30 MgSO4, 1.24 KH2PO4, 12 NaHCO3, and 10 glucose (pH = 7.8). All solutions were sterilized by filtration through 0.22-µm filters (Millipore, Molsheim, France) before injection.

Experimental animals. Adult rainbow trout Oncorhynchus mykiss (body wt 301 ± 6.5 g) were purchased locally and held in a circulating 1,000-liter tank containing dechlorinated, aerated tap water (11 ± 1°C) under a standard photoperiod (lights on 0900-2000). Fish were maintained under these conditions for at least 8 days before the beginning of the experiments. Animal manipulations were performed according to the recommendations of the French Ethical Committee and under the supervision of authorized investigators.

Surgical procedures. The surgical procedures for dorsal aorta cannulation, intracerebroventricular guide insertion, and ventral aorta Doppler probe placement have been described in detail previously (16-20). Briefly, trout were anesthetized by immersion in tricaine methanesulfonate (3- amino-benzoic acid ethyl ester; 60 mg/l in tap water buffered with NaHCO3 to pH = 7.3-7.5). The dorsal aorta was cannulated nonocclusively with PE-50 polyethylene tubing (Clay Adams). A 25-gauge needle fitted with a PE-50 catheter was inserted into the third ventricle of the brain so that injection of test substances occurred at the level of the preoptic nuclei. The intracerebroventricular injector was made from a 33-gauge stainless steel cannula connected with a PE-10 polyethylene tubing to a 10-µl Hamilton syringe. In some experimental fish (n = 8), the cardiac output (Q) was measured as follows. A midline incision was made through the skin and muscle immediately anterior to the base of the pectoral fins at a position overlying the ventral aorta, and a cuff-type Doppler probe (2.0 mm ID, Iowa Doppler Products; Iowa City, IA) was placed around the ventral aorta. The incision was sutured, and the leads from the flow probe were secured to the skin. After surgery, trout were transferred into individual 6-liter blackened chambers and supplied with partially recycled and aerated tap water (11 ± 1°C). Oxygen tension in the water tank (20.0 kPa) and pH (7.50-7.80) were continuously recorded and maintained at constant levels. A small horizontal aperture was made along the upper edge of the aquarium for connection of the dorsal aorta cannula and the Doppler probe leads and to permit intracerebroventricular injections of substances without disturbing the trout.

A review of stress responses in salmonid fish has reported that concentrations of plasma cortisol in rainbow trout rise from resting values in the range 5-25 ng/ml to between 63 and 297 ng/ml after handling or prolonged swimming (9). We have determined plasma cortisol levels in the cannulated and confined trout used in the present study. These concentrations were 44 ± 6 ng/ml measured 24 h after surgery and 42 ± 7 ng/ml measured 72 h after surgery. We conclude, therefore, that the animals were not subject to severe stress and that there was no advantage to delaying experimentation beyond 24 h postsurgery.

Experimental protocols. Trout were left for 24 h to recover from surgery and to become accustomed to their new environment. Each day, the general appearence and behavior of trout, hematocrit, and cardiovascular parameters were monitored as previously described (16, 17). After stable baseline levels of mean dorsal aortic blood pressure (PDA) and heart rate (HR) had been maintained for ~2 h, the experimental regimen of intracerebroventricular or intra-arterial injections started. For all protocols, fish received a control injection of vehicle and, 30 min later, an injection of peptide. The animals usually received a single intracerebroventricular and a single intra-arterial injection of peptide per day in random order. When two injections were made in the same site, a delay of at least 6 h was made between the injections to avoid tachyphylaxis.

Intracerebroventricular administration of U-I. A group of 20 fish received intracerebroventricular injections of U-I. The injector was inserted into the intracerebroventricular guide, and once the cardiovascular parameters had stabilized, the recording session proceeded for 30 min. After 5 min of baseline recording, 0.5 µl of vehicle or 0.5 µl of U-I solution were injected over 30 s into the third ventricle. The injection was made through extension tubing so that no trout was handled during the test period. Preliminary experiments showed that intracerebroventricular injection of U-I, at doses over 50 pmol, caused marked agitations in the animals, and so the effects of U-I were investigated at doses of 1, 5, and 12.5 pmol. These doses are in the same range as those previously used for the study of the central cardiovascular effects of arginine vasotocin (19), angiotensin II (20), and endothelin-1 (16) in trout.

Intra-arterial administration of U-I. A total of 45 fish received intra-arterial injections of U-I. After 5 min baseline recording, 50 µl of vehicle or U-I (12.5, 25, 50, 100, 250, and 500 pmol) were injected through the dorsal aorta. Each injection was immediately followed by 150 µl of vehicle to clear the cannula. To prevent the recording of the pressure artifact due to the injection, the computer was stopped for 10 s immediately after intra-arterial injections.

In a group of 10 trout, the alpha -adrenoreceptor antagonist prazosin (1 mg/kg) was injected via the dorsal aorta, and, 4 h later, U-I (500 pmol) was subsequently administered. This dose of antagonist was chosen according to a previous in vivo study (1). The efficacy of the alpha -adrenoreceptor blockade was tested by intra-arterial injection of norepinephrine (3.75 nmol/kg) before and after the recording session.

Recording of PDA, HR, and Q and processing of data. The heparinized aortic cannula was connected to a pressure transducer P23 ID (Gould Electronique, Ballainvilliers, France) that was calibrated every day with a static water column. The leads from the Doppler flow were attached to a Doppler flowmeter (University of Iowa, Iowa City, IA). The zero-flow level was set electronically, and the range gate controls of the Doppler unit were adjusted to record the highest output signal. Thereafter, the mean signal was continuously recorded as kilohertz of Doppler shift (Delta kHz). The mean PDA, HR, Q, and the systemic vascular resistance (Rs = PDA/Q) were calculated offline by the computer for the preinjection period (control period, 0-5 min) and the postinjection period (5-30 min). The mean maximum value of these parameters was determined during the postinjection period (5-30 min). For the calculation of Rs, central venous blood pressure was assumed to be zero and not to change during the experiment. Results for cardiovascular parameters are expressed either as absolute values (HR in beats/min, PDA in kPa), arbitrary units (Q in Delta kHz, Rs in kPa/Delta kHz), or percentages of the control values.

Isolated vessels. For this study, rainbow trout were supplied by Anten trout farm (Alingsås, Sweden) and kept in large tanks with circulating, aerated freshwater at 10°C. The fish (470-690 g; n = 7) were killed by a sharp blow to the head, and branches of the dorsal aorta supplying the skeletal muscle were dissected free from surrounding tissues. Segments of the arteries (~2 mm; ID 203-496 µm) were mounted on thin wires in a myograph apparatus (J. P. Trading, Aarhus, Denmark). The preparations were held in a bath containing 12 ml trout Ringer solution (pH 7.8) bubbled with 0.3% CO2 in air at 10°C (11). Changes in isometric tension were displayed on a Kipp and Zonen pen recorder. The length-passive tension relationship was determined for each vessel, and the internal circumference and lumen diameter was calculated assuming a transmural pressure of 4 kPa. The artery was then set to this tension for the rest of the experiment (12, 24).

To test the viability of the preparations, they were stimulated three times with KCl (60 mM) and adrenaline (10 µM) with multiple washes in between, as described by Kågström and Holmgren (12). After 30 min of recovery, the vessels were precontracted with epinephrine (10 µM), and when a steady plateau was reached, trout U-I was cumulatively added to the bath in the concentration range 10-10 to 3 × 10-7 M. The response to U-I was calculated as the percent reduction of the contraction produced by epinephrine (10 µM).

In a further series of experiments, arterial vascular rings (n = 6), preconstricted with epinephrine (10 µM) as previously described, were incubated with trout U-I (10-8 M) as the percent relaxation was measured. After extensive washing of the tissue and reequilibration for 1 h, the effect of trout U-I (10-8 M) on the preconstricted rings was measured in the presence of indomethacin (10-6 M) and nitro-L-arginine methyl ester (L-NAME; 3 × 10-4 M).

Statistical analysis. Values are expressed as means ± SE. Data were analyzed by Student's paired t-test or by one-way analysis of variance with repeated measures followed by Dunnett's test. Effects of drugs on the ability of U-I to constrict vascular tissue in vitro were analyzed by Wilcoxon's matched-pairs signed-ranks test. The significance level for statistical tests was P < 0.05.


    RESULTS
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

Hemodynamic effects of intracerebroventricular injections of U-I. Intracerebroventricular injections of vehicle only or 1 pmol of trout U-I were without effect on the hemodynamic parameters (time course data not shown). As shown in Fig. 1, intracerebroventricular administration of U-I (5 pmol) produced a progressive and significant elevation of PDA that reached a maximum value 15 min after the injection of the peptide [change in (Delta ) PDA = 0.78 ± 0.14 kPa] and remained elevated for at least a further 30 min. During this hypertensive phase, HR did not change. U-I produced a sustained increase in Q with a significant effect observed 10 min after the injection of the peptide (Delta Q = 18.9 ± 6.8%). Rs was unaffected after intracerebroventricular injection of U-I. Table 1 summarizes the central cardiovascular effects of U-I on PDA and HR after intracerebroventricular injection of increasing doses of U-I (1-12.5 pmol) and demonstrates that the maximum effect of U-I on PDA is reached at the dose of 5 pmol.


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  		Fig. 1.   Cardiovascular effects of intracerebroventricular (ICV) injection of 5 pmol of urotensin (U)-I on heart rate (HR), mean dorsal aortic blood pressure (PDA), cardiac output (Q), and systemic vascular resistance (Rs) in the unanesthetized trout. The arrowhead indicates when the injection was given. Each trace represents means ± SE (at selected times) of 6 independent experiments. * P < 0.05 vs. 0- or 5-min time points. bpm, Beats/min; Delta , change.


                              
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  		Table 1.   Changes in heart rate and mean PDA in unanesthetized trout in response to intracerebroventricular or intra-arterial injections of trout U-I

Hemodynamic effects of intra-arterial injections of U-I. Intra-arterial injection of vehicle only was without effect on the hemodynamic parameters (time course data not shown). The effect of intra-arterial injection of a relatively high dose of U-I (500 pmol) on HR, PDA, Q, and Rs is shown in Fig. 2. U-I produced a progressive and significant increase in PDA that peaked 7-8 min after the injection of the peptide (Delta PDA = 1.24 ± 0.28 kPa) with a return to basal pressures 7-8 min after this peak value. No change in HR was observed, but the peptide produced a significant decrease in Q. The maximum effect occurred 6-8 min after the injection of the peptide (Delta Q = -21.8 ± 5.4%) followed by a progressive increase so that, at the end of the recording, Q was significantly elevated compared with preinjection values (Delta Q = +20.3 ± 7.3%). After injection of the peptide, the calculated Rs significantly increased and reached a peak value by 6-7 min (Delta Rs = + 61.5 ± 16.9%). Rs returned to baseline level by 15 min after the injection of the peptide.


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  		Fig. 2.   Effects of intra-arterial (IA) injection of 500 pmol of U-I on HR, PDA, Q, and Rs in the unanesthetized trout. The arrowhead indicates when the injection was given. Each trace represents means ± SE (at selected times) for 8 independent experiments. * P < 0.05 vs. 0- or 5-min time points.

The concentration dependence of the hypertensive effect of intra-arterial injections of U-I (12.5-500 pmol) was investigated in trout bearing only the dorsal aorta cannula. U-I induced a dose-dependent increase in PDA (Table 1). The peak value in PDA was always observed 6-8 min after the injection of the peptide, whatever the doses used. In this group of animals, the basal HR was significantly reduced compared with trout equipped with a Doppler flow probe (58.5 ± 4.9 vs. 63.9 ± 2.5 beats/min). U-I produced a delayed increase in HR with maximal effect occurring about 20 min after the injection of the peptide. The effect on HR was not dose dependent.

Effect of prazosin on the intra-arterial effects of U-I. Intra-arterial injection of prazosin alone produced a significant fall in PDA (Delta PDA = -0.48 ± 0.21 kPa) without significant change in HR. In all test animals, the rise in PDA produced by norepinephrine (3.75 nmol/kg) was completely abolished by pretreatment with prazosin (Delta PDA = -0.27 ± 0.10 kPa vs. 1.59 ± 0.17, n = 10). As shown in Fig. 3, alpha -adrenergic blockade also completely abolished the hypertensive effect observed following intra-arterial injection of U-I (500 pmol). In contrast, the peptide produced a long-lasting and significant hypotensive response (Delta PDA = -0.62 ± 0.20 kPa) concomitant with a significant increase in HR (Delta HR = +12.1 ± 2.9 beats/min).


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  		Fig. 3.   Cardiovascular effects of IA injection of 500 pmol of U-I on HR and PDA after pretreatment of trout with prazosin (Prazo). The arrowhead indicates when the injection was given. Each trace represents means ± SE (at selected times) for 10 independent experiments. * P < 0.05 vs. 0- or 5-min time points.

Effects of U-I on isolated trout vessels. Trout U-I produced a concentration-dependent (pD2 = 7.74 ± 0.08) relaxation of isolated vascular rings from the dorsal aorta that had been precontracted to constant tension with epinephrine (Fig. 4). Maximum relaxation was produced by 10-7 M U-I and represented 54 ± 11% of the initial tension. The inhibitor of prostaglandin synthesis, indomethacin (10-6 M), was without significant effect on the ability of trout U-I (10-8 M) to reduce tension in the rings (34.5 ± 5.7% vs. 28.6 ± 8.0% relaxation in the presence and absence of indomethacin; n = 6). Similarly, the inhibitor of nitric oxide synthesis, L-NAME (3 × 10-4 M) was also without significant effect on relaxation (18.2 ± 5.1% vs. 17.2 ± 5.1% relaxation in the presence and absence of L-NAME; n = 6).


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  		Fig. 4.   Effects of increasing concentrations of synthetic trout U-I on the relaxation of tension of isolated vascular rings from trout dorsal aorta. The rings were preconstricted with epinephrine (10 µM). Data points show means ± SE for 7 independent experiments.


    DISCUSSION
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

This study complements our earlier work on the central and peripheral cardiovascular effects of synthetic trout U-II in unanesthetized trout (18). The results were obtained using the same experimental conditions so that they allow direct comparison of the data. The central hypertensive effects of U-II in trout were observed only after intracerebroventricular injection of a high dose (500 pmol) of the peptide (18). In contrast, the present study demonstrates that a significant hypertensive effect was observed after intracerebroventricular injection of a 100-fold smaller dose of U-I, suggesting that structures within the central nervous system are particularly sensitive to the action of U-I. In this context, the minimum effective dose of U-I is comparable with the low picomole doses of arginine vasotocin (5 pmol) and endothelin-I (12.5 pmol) that were required to elicit a significant hypertensive effect after intracerebroventricular injection in trout (16, 19). In the unanesthetized rat, intracerebroventricular injection of CRH (0.15-1.5 nmol) produced elevations of arterial blood pressure, an increase in HR, and altered baroreflex control of HR (7). The increase in arterial blood pressure was shown to arise from an enhanced Q (26). Our study has demonstrated that trout U-I, a peptide that shows 60% amino acid-sequence identity to rat/human CRH (21), also acts centrally to produce an increase in blood pressure that is mediated by an enhanced Q. This result suggests that the central cardiovascular effects of the CRH/U-I family of neuroendocrine peptides have been well conserved during vertebrate evolution.

U-I is not confined to the caudal neurosecretory system of fish. In the white sucker, immunocytochemistry has demonstrated the presence of U-I immunoreactivity in neuronal fibers within the spinal cord, the brain stem, the hypothalamus, and the telencephalon (31, 32). In the sucker and goldfish, a U-I-like peptide was also detected in neuronal perikarya of the lateral tuberal area together with U-I-encoding mRNA (15). In addition, 125I-labeled U-I binding sites (putative receptors) are present in the brain of the goldfish (14). Taken together, these anatomical results and our functional data suggest that U-I may be regarded as a neurotransmitter and/or neuromodulator acting within the brain and involved in central cardiovascular regulation. Although the present study was not designed to determine the site(s) of action of the exogenously administered U-I, speculation can be made. Because the peptide is injected within the third ventricle of the brain, it may act first on the hypothalamus, an area involved in neuroendocrine and neurogenic control of the cardiovascular functions. Exogenous U-I may also diffuse within the cerebrospinal fluid compartment to reach directly brain stem or spinal cord nuclei involved in cardiovascular regulation.

Intra-arterial injection of U-I (500 pmol) in trout equipped with a Doppler flow probe and an aortic cannula produced a dose-dependent increase in PDA without change in HR. In trout that were less instrumented (aortic cannula only), HR was lower, indicative of tonic parasympathetic drive to the heart, and intra-arterial injection of U-I produced a delayed and non-dose-dependent increase in HR. These results stand in marked contrast to the effects of other neurohormonal peptides in the same animal model. For example, the hypertensive effects after intra-arterial administration of arginine vasotocin (19), angiotensin II (20), U-II (18), and endothelin-1 (16) were always associated with a significant bradycardia. This bradycardia is mediated by the parasympathetic system (Ref. 20 and J. C. Le Mével, unpublished data). Although the baroreflex system loop in fish is not well understood, the cardiac response is presumed to be reflexogenic. The absence of bradycardia after the injection of U-I suggests either that U-I blunted the cardioinhibitory baroreflex response or that the decrease in HR, which may be reflexogenically triggered when PDA increases, is counteracted by a positive chronotropic mechanism. Whether U-I itself acts directly on the heart to increase its freqency or whether adrenergic mechanisms are recruited for this response remains to be determined. The delayed increase in HR that appeared in less-stressful experimental situations may be related to a decrease in vagal tone to the heart after the hemodynamic perturbations induced by intra-arterial injection of U-I. Consisent with a previous study using the rat mesenteric artery (25), U-I elicits a dose-dependent vasorelaxation response in isolated vessels of the trout that is not mediated through synthesis of prostaglandins or nitric oxide. This result suggests that the hypertensive action observed in vivo after the intra-arterial injection of the peptide is indirectly mediated. Consistent with this hypothesis, pretreatment of trout with prazosin, an alpha -adrenergic-receptor antagonist, completely abolished the hypertensive phase usually observed after intra-arterial injection of U-I in control trout. In contrast, sustained hypotension was observed in prasozin-treated fish, and the decrease in PDA was accompanied by tachycardia. The increase in HR may be reflex in nature, although a direct action of the peptide on the heart or an activation of beta -adrenergic receptors cannot be excluded. Thus our in vivo results suggest that the primary cardiovascular effect of U-I in trout is to induce hypotension, as observed in mammals (10, 22). Thereafter, a rapid release of catecholamines compensates for this fall in blood pressure. Our results are in accordance with recent studies in the dogfish S. canicula, showing that the primary effect of dogfish U-I is probably to induce vasodilatation and that the constrictor action of catecholamines reversed this effect (27). However, the threshold dose for eliciting a significant cardiovascular response in trout (50 pmol) is much more lower than the dose required to induce a change in the blood pressure of the dogfish (500 pmol). The circulating concentrations of U-I in fish have not been determined so it is not known whether the threshold levels of U-I for effects on PDA in vivo or for effects on vascular smooth muscle in vitro measured in this study are reached in a physiological situation. However, as previously pointed out by Bern et al. (3), the concentration of U-I secreted into veins draining the renal portal system, the intestine, and the hepatic areas may be relatively high so that U-I may exercise a paracrine or locally acting hemodynamic action.

Perspectives

Our functional studies have demonstrated that both U-I and -II (18) can evoke profound changes in the hemodynamic parameters of unanesthetized trout acting either through the central nervous system or on peripheral tissues. The discovery of a potent and sustained central hypertensive action of U-I, but not of U-II, together with the previously described neuroendocrine effects of U-I on the activation of the corticotropic axis (13) suggests that U-I may be regarded as one of the CRH family of neuropeptides involved in the endocrine and cardiovascular adaptation of the organism to stress. In the periphery, U-I acts primarly as a vasorelaxant, but hypotension in the animal is rapidly reversed by the release of catecholamines leading to transient hypertension. In contrast, U-II exerts a direct vasoconstrictory action leading to a systemic hypertension of long duration. Consequently, the two urotensins appear to exert quite distinct cardiovascular effects in the periphery. Because these two biosynthetically unrelated peptides are colocalized within neurons of the caudal neurosecretory system (3, 14), it is important to determine the physiological stimuli that trigger either the corelease or the differential release of these peptides. By subtle actions through the cardiovascular system, these two neuroendocrine peptides may permit a fine control of the perfusion of organs such as the kidney, liver, and intestine.


    ACKNOWLEDGEMENTS

We thank Martine Simon for typing the manuscript.


    FOOTNOTES

This study was supported by grants from the Institut de Synergie des Sciences et de la Santé-Brest, National Science Foundation (IBN-9806997) and by a North Atlantic Treaty Organization Collaborative Research Grant (CRG.CRG972998).

Address for reprint requests and other correspondence: J. M. Conlon, Dept. of Biomedical Sciences, Creighton Univ. Medical School, Omaha NE 68178-0405 (E-mail: jmconlon{at}creighton.edu).

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.

Received 14 December 1999; accepted in final form 24 February 2000.


    REFERENCES
TOP
ABSTRACT
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES

1.   Axelsson, M, Davison B, Forster M, and Nilsson S. Blood pressure control in the antarctic fish Pagothenia Borchgrevinki. J Exp Biol 190: 265-279, 1994[Abstract].

2.   Barsyte, D, Tipping DR, Smart D, Conlon JM, Baker BI, and Lovejoy DA. Rainbow trout (Oncorhynchus mykiss) urotensin-I: structural differences between urotensins-I and urocortins. Gen Comp Endocrinol 115: 169-177, 1999[ISI][Medline].

3.   Bern, H, Pearson D, Larson BA, and Nishioka RS. Neurohormones from fish tails: the caudal neurosecretory system. I. "Urophysiology" and the caudal neurosecretory system of fishes. Rec Prog Horm Res 41: 533-552, 1985.

4.   Chan, DKO Cardiovascular and renal effects of urotensins I and II in the eel, Anguilla rostrata. Gen Comp Endocrinol 27: 52-61, 1975[ISI][Medline].

5.   Conlon, JM, Yano K, Waugh D, and Hazon N. Distribution and molecular forms of urotensin II and its role in cardiovascular regulation in vertebrates. J Exp Zool 275: 226-238, 1996[ISI][Medline].

6.   Donaldson, CJ, Sutton SW, Perrin MP, Corrigan AZ, Lewis KA, Rivier JE, Vaughan JM, and Vale WW. Cloning and characterization of human urocortin. Endocrinology 137: 2167-2170, 1996[Abstract].

7.   Fisher, LA. Central autonomic modulation of cardiac baroreflex by corticotropin-releasing factor. Am J Physiol Heart Circ Physiol 256: H949-H955, 1989[Abstract/Free Full Text].

8.   Fryer, J, Lederis K, and Rivier J. Urotensin-I, a CRF-like neuropeptide, stimulates ACTH from the teleost pituitary. Endocrinology 113: 2308-2310, 1983[Abstract].

9.   Gamperl, AK, Vijayan MM, and Boutelier RG. Experimental control of stress hormone levels in fishes: techniques and applications. Rev Fish Biol Fisheries 4: 215-255, 1994.

10.   Hermus, ARMM, Pieters GFFM, Willemsen JJ, Ross HA, Smals AGH, Benraad TJ, and Kloppenborg PWC Hypotensive effects of ovine and human corticotrophin-releasing factors in man. Eur J Clin Pharmacol 31: 531-534, 1987[ISI][Medline].

11.   Jensen, J, and Conlon JM. Effects of trout bradykinin on the motility of the trout stomach and intestine: evidence for a receptor distinct from mammalian B1 and B2 subtypes. Br J Pharmacol 121: 526-530, 1997[ISI][Medline].

12.   Kågström, J, and Holmgren S. Calcitonin gene-related (CGRP), but not tachykinins, cause relaxation of small arteries from rainbow trout gut. Peptides 19: 577-584, 1998[ISI][Medline].

13.   Kelsall, CJ, and Balment RJ. Native urotensins influence cortisol secretion and plasma cortisol concentration in the euryhaline flounder, Platichthys flesus. Gen Comp Endocrinol 112: 210-219, 1998[ISI][Medline].

14.   Lederis, K, Fryer J, Rivier J, MacCannell KL, Kobayashi Y, Woo N, and Wong KL. Neurohormones from fish tails. II. Actions of urotensin-I in mammals and fishes. Rec Prog Horm Res 41: 553-576, 1985.

15.   Lederis, K, Ichikawa T, Richter D, and Schõnrock C. Molecular analysis of corticotropin-releasing factors and related peptides in teleosts. In: Biochemistry and Molecular Biology of Fishes, edited by Hochachka P, and Mommsen TP.. Amsterdam: Elsevier, 1993, p. 235-338.

16.   Le Mével, JC, Delarue C, Mabin D, and Vaudry H. Central and peripheral administration of endothelin-1 induces an increase in blood pressure in conscious trout. Am J Physiol Regulatory Integrative Comp Physiol 276: R1010-R1017, 1999[Abstract/Free Full Text].

17.   Le Mével, JC, Mabin D, Hanley AM, and Conlon JM. Contrasting cardiovascular effects following central and peripheral injections of trout galanin in trout. Am J Physiol Regulatory Integrative Comp Physiol 275: R1118-R1126, 1998[Abstract/Free Full Text].

18.   Le Mével, JC, Olson KR, Conklin D, Waugh D, Smith DD, Vaudry H, and Conlon JM. Cardiovascular actions of trout urotensin II in the conscious trout, Oncorhynchus mykiss. Am J Physiol Regulatory Integrative Comp Physiol 271: R1335-R1343, 1996[Abstract/Free Full Text].

19.   Le Mével, JC, Pamantung TF, Mabin D, and Vaudry H. Effects of central and peripheral administration of arginine vasotocin and related neuropeptides on blood pressure and heart rate in the conscious trout. Brain Res 610: 82-89, 1993[ISI][Medline].

20.   Le Mével, JC, Pamantung TF, Mabin D, and Vaudry H. Intracerebroventricular administration of angiotensin II increases heart rate in the conscious trout. Brain Res 654: 216-222, 1994[ISI][Medline].

21.   Lovejoy, DA, and Balment RJ. Evolution and physiology of the corticotropin-releasing factor (CRF) family of neuropeptides in vertebrates. Gen Comp Endocrinol 115: 1-22, 1999[ISI][Medline].

22.   MacCannell, KL, and Lederis K. Dilatation of the mesenteric vascular bed of the dog produced by a peptide, urotensin I. J Pharmacol Exp Ther 203: 38-46, 1977[Abstract/Free Full Text].

23.   Morley, SD, Schonrock C, Richter D, Okawara Y, and Lederis K. Corticotropin-releasing factor (CRF) gene family in the brain of the teleost fish Catostomus commersoni (white sucker): molecular analysis predicts distinct precursors for two CRFs and one urotensin I peptide. Mol Mar Biol Biotechnol 1: 48-57, 1991[Medline].

24.   Mulvany, MJ, and Halpern W. Contractile properties of small arterial resistance vessels in spontaneously hypertensive and normotensive rats. Circ Res 41: 19-26, 1977[Free Full Text].

25.   Muramatsu, I, Miura A, Fujiwara M, and Lederis K. Rat isolated mesenteric artery: a sensitive preparation for the bioassay of urotensin I. Gen Comp Endocrinol 45: 446-452, 1981[ISI][Medline].

26.   Overton, JM, Davis-Gorman G, and Fisher LA. Central nervous effects of CRF and angiotensin II on cardiac ouptput in conscious rats. J Appl Physiol 69: 788-791, 1990[Abstract/Free Full Text].

27.   Platzack, B, Schaffert C, Hazon N, and Conlon JM. Cardiovascular actions of dogfish urotensin I in the dogfish, Scyliorhinus canicula. Gen Comp Endocrinol 109: 269-275, 1998[ISI][Medline].

28.   Vaughan, J, Donaldson C, Bittencourt J, Perrin MH, Lewis K, Sutton S, Chan R, Turnbull AV, Lovejoy D, Rivier C, Rivier J, Sawchenko PE, and Vale W. Urocortin, a mammalian neuropeptide related to fish urotensin I and to corticotropin-releasing factor. Nature 378: 287-292, 1995[Medline].

29.   Waugh, D, Anderson G, Armour KJ, Balment RJ, Hazon N, and Conlon JM. A peptide from the caudal neurosecretory system of the dogfish, Scyliorhinus canicula, that is structurally related to urotensin I. Gen Comp Endocrinol 99: 333-339, 1995[ISI][Medline].

30.   Woo, NYS, and Bern HA. Vasoactive properties of urotensin I and II in a Columbiform and three Galliform birds, and a bioassay for urotensin I. J Comp Physiol 126: 193-202, 1978.

31.   Yulis, CR, and Lederis K. The distribution of "extraurophyseal" urotensin-I-immunoreactivity in the central nervous system of Catostomus commersoni after urophysectomy. Neurosci Lett 70: 75-80, 1986[ISI][Medline].

32.   Yulis, CR, Lederis K, Wong KL, and Fisher AWF Localization of urotensin-I- and corticotropin-releasing factor-like immunoreactivity in the central nervous system of Catostomus commersoni. Peptides 7: 79-86, 1986[ISI][Medline].

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