Comparative hemodynamic effects of hypotension induced by CGRP and PGE1 in dogs

Calcitonin gene-related peptide (CGRP) produces vasodilation, hypotension, and tachycardia. We compared the hemodynamic effects of CGRP-induced hypotension with the effects of prostaglandin E1 (PGE1), which is currently used as a hypotensive agent during anesthesia. Eighteen mongrel dogs were anesthetized with pentobarbital (25 mg·kg(-1)), and 0.87% halothane in oxygen (1MAC). Measurements of hemodynamic variables were made before, during, and after induced hypotension. The mean arterial pressure (MAP) was lowered to 60 mmHg by the infusion of either CGRP (n=10) or PGE1 (n=8). This decrease in MAP was appoximately 50% of the baseline value. The CGRP- and PGE1-induced hypotension resulted in 61% and 51% maximum reductions (P<0.01, respectively) in systemic vascular resistance associated with a significant increase in stroke volume index; the two treatments, however produced inconsistent changes in cardiac index (CI). With CGRP, a maximum increase of 144% (P< 0.01) in CI was observed during induced hypotension. In contrast, PGE1-induced hypotension caused no significant changes in CI throughout the observation period. Left ventricular maximum dP/dt decreased (P<0.01) during the hypotensive period with PGE1, whereas it remained un-changes during CGRP-induced hypotension. The different results for changes in CI and cardiac contractility during the CGRP- and PGE1-induced hypotension were probably due to differences in ventricular filling pressure. Hypotension induced by PGE1 was associated with a significant decrease in heart rate (HR), whereas CGRP did not affect HR. This study shows that both CGRP and PGE1 are effective in decreasing afterload and in inducing hypotension; the results suggest that CGRP is a useful vasodilator for inducing hypotension during halothane anesthesia.