Exaggerated natriuresis after selective AT1 receptor blockade in Dahl salt-sensitive rats

Salt-sensitive individuals are susceptible to develop hypertension when exposed to high salt-diet. Such a phenomenon is considered to be due to a genetic impairment in the renal excretion of sodium. In the present studies extent of endogenous angiotensin-II (Ang-II) mediated antinatriuresis was comparatively evaluated in Dahl salt-sensitive (SS) and salt-resistant (SR) rats, using a selective AT(1) receptor antagonist, candesartan. In addition, differences in plasma renin activity and characteristics of Ang-II receptors in the renal cortical tubular membranes were also examined. Under INACTIN (R) anesthesia AT(1) receptor blockade resulted in significant increases in renal sodium excretion, which was several-fold greater in SS rats than that observed in SR rats. These observations suggest that antinatriuretic function of endogenous angiotensin-II is exaggerated in SS rats. This functional overexpression appears to be related to an increase in the affinity of Ang-II receptors in renal cortical tubular membranes but not to receptor density or plasma renin activity. It is proposed that salt-dependent hypertension in Dahl salt-sensitive rats may be due to enhanced Ang-II mediated sodium retention.