Regulation of glomerular angiotensin II receptors in renovascular hypertension: absence of response to variations in salt intake

Differential actions of renal ischemic injury on the intrarenal angiotensin system

The present study determined the effect of either occlusion of the left renal artery for 60 min (ischemia) or sham operation on angiotensin (ANG) receptors and tissue and urinary levels of ANG peptides between 24 and 72 h recovery in male Sprague-Dawley rats. At 24 h postischemia, urinary concentrations of ANG I and ANG-(1-7) rose by an average of 83 and 64%, respectively (P < 0.05) but had declined to control levels by 72 h. Tissue ANG II rose at 24 h in postischemic kidneys by an average of 63% compared with the contralateral nonischemic kidney (P < 0.05). Whereas the enzymatic activity of angiotensin-converting enzyme and neprilysin was reduced after ischemia, renal renin activity in ischemic kidneys rose by 74% compared with sham-operated kidneys. Receptor autoradiography using (125)I-labeled [Sar(1),Thr(8)]ANG II ((125)I-Sarthran) (0.8 nM) revealed a decreased apparent density of ANG receptors (>80% AT(1)) in ischemic kidneys with a trend for a decrease in the contralateral nonischemic kidneys compared with the kidneys from sham-operated rats. Twenty-four hours after ischemia, ANG II receptors decreased by 68% in glomeruli (P < 0.05), 49% in the outer cortical tubulointerstitial area (P < 0.05), and 48% in the inner cortical-outer medullary area of the vasa recta (P < 0.05). Medullary binding decreased approximately 50% in both the ischemic kidney and the contralateral nonischemic kidney compared with sham. In all regions of the ischemic kidney, receptors recovered by 72 h to levels not different from sham control rats. The marked change in urinary ANG I and ANG-(1-7) at 24 h following occlusion indicates these peptides may be potential urinary markers for acute renal ischemia. The reduction of receptors in vascular and tubular regions of the ischemic kidney provides a mechanism for the loss of vasoconstrictor responses to ANG II following ischemia previously reported by others.

Regulation of glomerular angiotensin II receptor densities in renovascular hypertension: response to reduced sympathetic and vasopressin influence

The regulation of the density of angiotensin II receptors in renal glomeruli in response to changes in salt intake is altered in Sprague-Dawley rats with renovascular hypertension due to aortic constriction, and in hypertensive salt-sensitive Dahl rats (Sahlgren 1989, Sahlgren & Aperia 1989). This study examines the modulatory role of sympathetic activity and arginine-vasopressin on angiotensin II receptors in hypertensive Sprague-Dawley rats with aortic constriction as well as in normotensive control rats. Denervation of the left kidney caused a 50% increase in the glomerular angiotensin II receptor density in the denervated kidney in both hypertensive rats and normotensive controls. An even more marked increase in glomerular receptor density occurred in both hypertensive rats and controls after blocking the sympathetic nervous system with guanethidine. To block the effects of arginine-vasopressin we used a blocker of the V1-receptors (predominant in vessels) and found an approximately 100% increase in the glomerular receptor density of angiotensin II in rats with aortic constriction. There was no reduction in blood pressure. Thus, on the receptor level the renin-angiotensin system is markedly influenced by the activity of other major pressor systems.

Renal hypertension following aortic constriction is abolished by angiotensin II converting enzyme inhibitor, but not by low-salt diet

This study evaluates the role of different sodium intakes and the role of angiotensin II in the development and the maintenance of renovascular hypertension in rats with constriction of the aorta proximal to the renal arteries. The rats were studied 3 weeks after surgery when the hypertension was well established. Glomerular filtration rate was decreased and filtration fraction was increased in rats with proximal aortic constriction. Low and high salt intakes had no effect on glomerular filtration and filtration fraction. Treatment with angiotensin II converting enzyme inhibitor increased the glomerular filtration rate and reduced the filtration fraction in rats with proximal aortic constriction to the same levels as in control rats. Serum levels of angiotensin II were about the same in rats with proximal aortic constriction as in control rats. Conclusion. The renovascular hypertension in proximal aortic constriction is influenced by locally formed angiotension II but not by alterations in salt intake.