Protective effects of angiotensin AT1 receptor blockade in malignant hypertension in the rat

We investigated the role of angiotensin II and endothelin-1 using the angiotensin AT1 receptor antagonist losartan and the endothelin ETA receptor antagonist atrasentan, in malignant hypertension and renal failure and damage induced by nitric oxide (NO) synthase inhibition in Harlan Sprague-Dawley (SD) rats. We also evaluated whether the protective effects of losartan go beyond the blood pressure reduction. Within only 3 weeks of treatment with the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME), Harlan SD rats developed malignant hypertension with renal failure and injuries. The latter were comprised of fibrinoid necrosis of small arteries and glomerular and tubular necrosis. Although both losartan and atrasentan attenuated the development of hypertension and renal failure, losartan only prevented the renal damage. In contrast to antrasentan, the vasodilator hydralazine reduced blood pressure and prevented the renal injuries similar to losartan. However, when these treatments were prolonged to 5 weeks, losartan, but not hydralazine, was still effective in reducing renal failure and damage, despite a marked increase in blood pressure. Our results indicate that angiotensin II and endothelin-1 play a differential role in the pathogenesis of malignant hypertension and in vascular and renal damage induced by L-NAME in Harlan SD rats. Although the protective effects of atrasentan may depend on the reduction of blood pressure, which was shown to retard the development of renal injury using hydralazine, those of losartan go beyond the blood pressure reduction. Hence, tissue protective effects of angiotensin AT1 receptor blockade may be pivotal for long-term vascular and renal protection.