LOCAL VERSUS CENTRAL EFFECT OF HALOTHANE ON CAROTID-SINUS BARORECEPTOR FUNCTION

The depressive effect of halothane on carotid sinus baroreceptor function may be due to direct local action, action in the CNS or both. Dogs were anesthetized with pentobarbital and ventilated with O2. The carotid sinus of the recipient dog was isolated and perfused with blood from the common carotid artery of the donor dog. Blood from the recipient sinus was returned through its external carotid to the donor common carotid. Both carotid sinuses of the donor and the contralateral carotid sinus of the recipient dog received uninterrupted circulation. Carotid sinus nerve action portentials and lingual artery pressure of the isolated recipient sinus were recorded before and during steady-state end-tidal halothane concentrations of 0, 0.5, 1.0, 1.5, 2.0 and 2.5% in O2 given randomly first to the donor dog (to evaluate direct local effect) and then to the recipient dog (to determine central effect). The dog not given halothane received pentobarbital. Plots of normalized nerve activity vs. halothane concentrations showed approximately zero slope when the donor was given halothane but showed a significant decrease in nerve activity when the recipient was given halothane. Halothane appeared to have no direct local effect but caused depression of baroreceptor nerve activity, possibly via CNS inhibition of sympathetic efferents to the carotid sinus.