Halothane anesthesia suppresses reflex tachycardia caused by calcitonin gene-related peptide in dogs

Calcitonin gene-related peptide (CGRP) is known to produce vasodilation, hypotension, and tachycardia. To investigate the interaction between CGRP and anesthetics, the hemodynamic response to infusions of CGRP was studied in dogs anesthetized with halothane or pentobarbital. In halothane-anesthetized dogs given 0.4 μg·kg(-1) of CGRP, mean arterial pressure (MAP) did not change significantly. However, there was a significant reduction in systemic vascular resistance (SVR) associated with significant increases in cardiac index (CI) and stroke volume index (SVI). Higher doses (4 and 40 μg·kg(-1)) of CGRP produced dose-dependent decreases in MAP accompanied by a reduction in SVR. Further, both CI and SVI significantly increased at 4 μg·kg(-1) CGRP but remained unchanged at the 40 μg·kg(-1) infusion rate. Heart rate (HR) was not increased at all doses but was decreased at 40 μg·kg(-1). In pentobarbital-anesthetized dogs, CGRP at doses of 4 μg·kg(-1) produced a qualitatively similar cardiovascular responses as that observed in halothane-anesthetized dogs, but with one exception: HR was significantly increased. The results show that the hemodynamic profiles induced by CGRP during halothane or pentobarbital anesthesia are a decrease in MAP accompanied by a reduction in SVR and no consistent alterations in CI. However, CGRP effects on HR showed in a different way. The results also show that HR response differs depending on the anesthetics used: HR increases during pentobarbital anesthesia, while it does not increase during halothane anesthesia.