Central administration of PD 123319 or EXP-3174 inhibits effects of angiotensin II

Cardiovascular responses to intracerebroventricular angiotensin II (ANG II) were measured in conscious rats, chronically instrumented for the measurement of regional hemodynamics, over 4 consecutive days in the absence and presence of either the AT2 receptor antagonist, PD 123319 (experiment 1), or the AT1 receptor antagonist, EXP-3174 (experiment 2). Intracerebroventricular ANG II had pressor and bradycardic effects, which were associated with marked mesenteric and hindquarters vasoconstriction, and a small transient renal vasoconstriction. Both PD 123319 and EXP-3174, given intracerebroventricularly, abolished the cardiovascular response to intracerebroventricular ANG II, although the profiles of activity of the compounds were different. PD 123319 caused a slowly developing, but remarkably prolonged (1-2 days) inhibition of the effects of ANG II, whereas EXP-3174 caused an immediate inhibition of the effects of ANG II, although responses to ANG II had returned to control levels by the following day. These data suggest that the hemodynamic effects of ANG II may involve concurrent, and interdependent, activation of AT1 and AT2 receptors or that PD 123319 undergoes a unique biotransformation in the brain to some product(s) with AT1 receptor antagonist activity.