Interaction of isoflurane and cromakalim, a KATP channel opener, on coronary and systemic haemodynamics in chronically instrumented dogs.

Abstract

Although isoflurane has been shown to cause coronary and systemic vasodilation through KATP channel activation, the interaction of KATP channel openers and isoflurane has not been fully investigated. The present study was carried out to determine the haemodynamic actions of cromakalim, a KATP channel opener, under the conscious state and during isoflurane anaesthesia in chronically instrumented dogs. Fourteen dogs were chronically instrumented to measure systemic and coronary haemodynamics. Each dog was randomly assigned to receive doses of either cromakalim, 4 and 10 microg x kg(-1) i.v., or isoflurane, 2.1% end-tidal (1.5 MAC), plus cromakalim, 4 and 10 microg x kg(-1) i.v. Cromakalim dose-relatedly decreased mean arterial pressure and systemic vascular resistance and increased coronary blood flow in both conscious and anaesthetized states. With isoflurane, the duration of effects of cromakalim were prolonged. Isoflurane exerted an additive effect on the increase in coronary blood flow induced by a low-dose cromakalim, whereas it did not influence the effect of a high-dose cromakalim. The maximum rate of increase in left ventricular pressure and segment shortening were increased by cromakalim in the conscious state but unchanged during isoflurane anaesthesia. The results suggest that the coronary vasodilating effects of isoflurane and cromakalim are basically additive until cromakalim exerts the maximal effect, and that the action of cromakalim on the coronary vasculature is prolonged by isoflurane.