Segmental renal vascular resistance in the spontaneously hypertensive rat.
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.
D000375:Aging; D000818:Animals; D001794:Blood Pressure; D006973:Hypertension / Q000473:pathology / Q000503:physiopathology*; D007668:Kidney / Q000098:blood supply* / Q000473:pathology; D008297:Male; D009929:Organ Size; D051381:Rats; D011919:Rats, Inbred Strains; D014655:Vascular Resistance