Central and peripheral actions of a nonpeptidic angiotensin II receptor antagonist

Nonpeptidic imidazole derivatives were recently reported to be angiotensin II receptor antagonists with acute blood pressure-lowering activity. In the present study, we characterized the angiotensin II receptor antagonist properties of one such derivative, 4'-([2-butyl-4-chloro-5-(hydroxymethyl)-1H-imidazol-1-yl]methyl)- [1,1'-biphenyl]-2-carboxylic acid (IMI). In receptor binding studies, IMI displaced bound [125I]angiotensin II from rat uterine membranes with an IC50 of 0.17 microM. In isolated rabbit aortic rings, IMI shifted the angiotensin II concentration-response curve to the right in a parallel and concentration-dependent manner. A Schild plot of these data indicated a pA2 of 7.13 +/- 0.16 and a slope of 0.94 +/- 0.06. In rat kidney slices, IMI shifted the concentration-response curve for angiotensin II-induced inhibition of renin release to the right. Antagonism of the angiotensin II pressor response by IMI was dose dependent and reversible in ganglion-blocked, anesthetized rats. The water intake and pressor responses to intracerebroventricular angiotensin II (100 pmol) were inhibited by intracerebroventricular IMI (25 or 50 nmol) in conscious Sprague-Dawley rats. Similarly, the drinking and pressor responses to intravenous angiotensin II were blocked by intravenous IMI in conscious rats. IMI alone had no effects on mean arterial pressure or drinking when administered either intravenously or intracerebroventricularly. IMI decreased mean arterial pressure throughout 5 days of infusion in spontaneously hypertensive rats. In summary, IMI was a full competitive antagonist without partial agonist activity in peripheral tissues and the central nervous system. Moreover, the chronic administration of this angiotensin II receptor antagonist was antihypertensive in spontaneously hypertensive rats.