The effect of renal perfusion pressure on renal vascular resistance in the spontaneously hypertensive rat.

Renal hemodynamics and renal vascular resistance (RVR) were measured in the spontaneously hypertensive rat (SHR) and in the normotensive Wistar-Kyoto rat (WKY). In addition, the autoregulatory response and segmental RVR in the SHR were studied after aortic constriction. Mean arterial pressure (MAP) and RVR were higher in the SHR than in the WKY, but renal blood flow (RBF) and glomerular filtration rate were similar in both groups. Measurement of mean afferent arteriolar diameter (AAD) by a microsphere method showed a significantly smaller AAD in SHR (17.7 +/- 0.35 micrometers) than in the WKY (19.5 +/- 0.20 micrometers). This decrease in AAD could account for a 47% increase in preglomerular resistance. Aortic constriction in the SHR, sufficient to reduce renal perfusion pressure from 152 to 115 mmHg, did not alter the AAD. Since RBF and glomerular filtration were also well maintained following aortic constriction, these autoregulatory responses suggest that vessels proximal to the afferent arteriole rather than postglomerular vasculature are primarily involved in the changes on intrarenal vascular resistance in SHR.