AJP - Heart and Circulatory Physiology, Vol 242, Issue 6 961-H966, Copyright © 1982 by American Physiological Society
Segmental renal vascular resistance in the spontaneously hypertensive rat
C. H. Hsu, J. H. Slavicek and T. W. Kurtz
Renal hemodynamics were studied during different stages of development of
hypertension in unanesthetized spontaneously hypertensive rats (SHR). In
SHR at 4 wks of age mean arterial pressure (MAP) was higher than in
age-matched Wistar Kyoto rats (WKY); however, renal blood flow (RBF) and
renal vascular resistance (RVR) were not different between these two
groups. Mean values of RVR and MAP in 8- and 12-wk-old SHR were
significantly greater than those of age-matched WKY. Both RBF of 8- and
12-wk-old SHR were significantly lower than the corresponding values of
WKY. Afferent arteriolar diameter (AAD) was measured with a microsphere
method. AAD was not different between 4-wk-old SHR and WKY; however, the
AAD of 8-wk-old (16.3 +/- 0.23 micrometers, n = 5) and 12-wk-old (17.4 +/-
0.48, n = 5) SHR were significantly smaller than those of respective
control WKY (17.3 +/- 0.34, n = 4, P less than 0.05; 19.3 +/- 0.12, n = 5,
P less than 0.01). Calculated preglomerular (Rpre) and postglomerular
resistances (Rpost) of 12-wk-old SHR were increased 96 and 129% when
compared with respective segmental resistances of the control WKY. The
decrease in AAD of 12-wk-old SHR was sufficient to account for a 33%
increase in Rpre. After the rats were treated with hydralazine (0.5 mg/kg
iv), MAP, RBF, and RVR of SHR were not different from the control WKY
values. Rpre and Rpost of SHR were substantially decreased; however,
vasodilation occurred at vessels proximal and distal to the afferent
arteriole because AAD was not altered. Our results indicate that increased
RVR in SHR involves increases in Rpre and Rpost.
