Enalaprilat effects renin-angiotensin and adrenergic response to induced hypotension in the rabbit

The effects of enalaprilat on the renin-angiotensin system and sympathetic nervous system during sodium nitroprusside (SNP)-induced hypotension and halothane anesthesia were studied in three groups of New Zealand white rabbits. Two groups of rabbits (E and EH) were treated with an infusion of enalaprilat at 3.5 micrograms/kg/min i.v. One enalaprilat-treated group (EH) and the third, untreated group (H) received SNP to induce hypotension. In these two groups, the mean arterial blood pressure (MAP) was reduced by 40% for 150 min. Group E did not undergo SNP-induced hypotension and served to document the effects of enalaprilat alone during the 150-min study period. Arterial blood samples for norepinephrine (NE), epinephrine (EPI), and plasma renin activity (PRA) were drawn prior to and during hypotension, and during the recovery period. The SNP dose required to maintain the hypotension was continuously recorded. NE, EPI, and PRA all increased in group H, indicating activation of both the renin-angiotensin system and the sympathetic system during hypotension. The amount of SNP required by group H to maintain a 40% reduction in MAP correlated with circulating NE levels (p less than 0.001) and not PRA. In group EH, PRA levels rose sharply and remained elevated. Plasma NE and EPI levels increased slightly with a decline in the SNP dose requirement. Group E demonstrated a rise in PRA levels, accompanied by unchanged NE and EPI levels and MAP during the study period.(ABSTRACT TRUNCATED AT 250 WORDS)