AT ₁ Receptor Expression in Glomeruli from NO-Deficient Rats

Abstract

Chronic inhibition of nitric oxide synthase promotes renin-dependent hypertension and renal injury. The present study examines how renal angiotensin II receptors are expressed in this model. N^G-nitro- L-arginine methyl ester ( L-NAME) was given orally to rats for 1 month and was associated or not with captopril during the 4 last days of the administration. ¹²⁵I-[Sar¹, Ile⁸]-Ang II binding, AT₁mRNA and cytosolic calcium were studied in isolated glomeruli from L-NAME and control rats and in cultured mesangial cells from normal rats. Renal injury was marked in rats receiving L-NAME. Type I angiotensin II (AT₁₎ receptor number and mRNA expression were decreased (p < 0.05) in glomeruli isolated from L-NAME-treated rats compared with controls, unless they received captopril in combination. The low level of AT₁ receptor expression was associated with an attenuated rise of cytosolic calcium in response to angiotensin II. Angiotensin-converting enzyme activity in glomeruli and angiotensin II concentration in renal cortex were increased (p < 0.05) in rats receiving L-NAME alone, whereas aminopeptidase A activity was not modified. To better discriminate between the direct and indirect effects of nitric oxide deficiency, rat mesangial cells were exposed or not for 24 h to S-nitroso-N-acetyl penicillamine, a nitric oxide donor. Angiotensin II binding, AT₁ mRNA expression and calcium response to angiotensin II were decreased in presence of the nitric oxide donor (p < 0.01). These results suggest that the decrease of AT₁ receptor expression after 1 month of L-NAME treatment does not depend on a direct effect of nitric oxide deficiency but results from the high local angiotensin II concentration due to the stimulated angiotensin-converting enzyme activity. They also show that the renin-angiotensin dependence of this model of hypertension does not result from the overexpression of AT₁ receptors.