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LOCAL CONTROL OF CIRCULATION
Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545
Submitted 17 December 2002 ; accepted in final form 29 May 2003
We investigated dynamic characteristics of renal blood flow (RBF)
autoregulation and relative contribution of underlying mechanisms within the
autoregulatory pressure range in rats. Renal arterial pressure (RAP) was
reduced by suprarenal aortic constriction for 60 s and then rapidly released.
Changes in renal vascular resistance (RVR) were assessed following rapid step
reduction and RAP rise. In response to rise, RVR initially fell 5-10% and
subsequently increased 
20%, reflecting 93% autoregulatory efficiency
(AE). Within the initial 7-9 s, RVR rose to 55% of total response providing
37% AE, reaching maximum speed at 2.2 s. A secondary RVR increase began at 7-9
s and reached maximum speed at 10-15 s. Response times suggest that the
initial RVR reflects the myogenic response and the secondary tubuloglomerular
feedback (TGF). During TGF inhibition by furosemide, AE was 64%. The initial
RVR rise was accelerated and enhanced, providing 49% AE, but it represented
only 88% of total. The remaining 12% indicates a third regulatory component.
The latter contributed up to 50% when the RAP increase began below the
autoregulatory range. TGF augmentation by acetazolamide affected neither AE
nor relative myogenic contribution. Diltiazem infusion markedly inhibited AE
and the primary and secondary RVR increases but left a slow component. In
response to RAP reduction, initial vasodilation constituted 73% of total
response but was not affected by furosemide. The third component's
contribution was 9%. Therefore, RBF autoregulation is primarily due to
myogenic response and TGF, contributing 55% and 33-45% in response to RAP rise
and 73% and 18-27% to RAP reduction. The data imply interaction between TGF
and myogenic response affecting strength and speed of myogenic response during
RAP rises. The data suggest a third regulatory system contributing <12%
normally but up to 50% at low RAP; its nature awaits further
investigation.
renal circulation; afferent arteriole; glomerular arterioles; myogenic mechanism; tubuloglomerular feedback; vascular smooth muscle cells; macula densa cells; calcium channel blocker; furosemide; acetazolamide
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