Changes of hemodynamics and glomerular ultrafiltration in renal hypertension of rats

Changes of hemodynamics and glomerular ultrafiltration in renal hypertension of rats. Determinants of glomerular ultrafiltration were studied by micropuncture in clamped (N = 11) and unclamped (N = 7) kidneys of two-kidney Goldblatt rats and compared to 15 controls. Renin-dependence of hypertension (184 ± 9 [SD] mm Hg, 3 to 4 week's duration) was demonstrated by infusing the angiotensin-II-antagonist saralasin. In clamped kidney hydrostatic pressure in glomerular capillaries (PGC) was reduced to 56.5 ± 3.0 vs. 61.2 ± 3.4 mm Hg in controls, whereas renal perfusion pressure behind the clip was normal. Early proximal flow rate (EPFR) was decreased to 20.5 ± 0.8 vs. 25.8 ± 1.5 nl/min in controls, at an unchanged single nephron filtration fraction (SNFF), indicating a reduced glomerular plasma flow (SNGPF). Preglomerular vascular resistance (RA) was increased by 21%, but postglomerular resistance (RE) remained unchanged. In unclamped kidneys, PGC was increased to 65.0 ± 1.9, and pressures in peritubular capillaries (PC) were increased to 17.5 ± 1.6 mm Hg. PC/PGC ratios were significantly higher. EPFR was increased to 32.1 ± 1.9 nl/min, indicating, at an unchanged SNFF, an increased SNGPF. RA increased by 51%, whereas RE declined by 25%. The ultrafiltration coefficient was reduced by 24% in unclamped kidneys. The number of glomeruli was lower in clamped (24,590 ± 5,500) and was higher in unclamped kidneys (33,580 ± 4,110) compared to controls (29,240 ± 4,900). Our results indicate that in clamped kidneys an increase of RA causes a reduction of PGC and, hence, a reduction of pressure at the baroreceptor site which may be a trigger mechanism for renin release. In unclamped kidneys, adaptation of RA and RE to high perfusion pressure is nearly perfect, in terms of an active component of RE dilatation. Modifications de l'hémodynamique et de la filtration glomérulaire au cours de l'hypertension d'origine rénale chez le rat. Les déterminants de l'ultrafiltration glomérulaire ont été étudiés par microponction des reins clampés (N = 11) et non clampés (N = 7) de rats à deux reins préparés selon Goldblatt, et les résultats ont été comparés à 75 contrôles. La dépendance de l'hypertension (184 ± 9 [SD] mm Hg, durée 3 to 4 semaines) vis à vis de la rénine a été démontrée par la perfusion de l'antagoniste de l'angiotensine, la saralasine. Dans les reins clampés la pression hydrostatique dans le capillaire glomérulaire diminue à 56,5 ± 3,0 au lieu de 61,2 ± 3,4 mm Hg chez les