THE EFFECT OF AGE ON HALOTHANE-INDUCED ALTERATIONS OF CONTRACTILITY IN ISOLATED RAT AORTA

Aging is implicated as a factor which increases the susceptibility to volatile anesthetic-induced depression of the cardiovascular system. H owever, little is known regarding mechanisms responsible for this enha nced depression. Current experiments examined the effects of 1.2 and 2 .4 vol.% halothane on norepinephrine-induced contractility in endothel ium-intact and -denuded aortic preparations isolated from 4-, 14-, and 24-month-old Fischer-344 rats. Prior to exposure to halothane, endoth elium removal significantly enhanced the sensitivity to norepinephrine in all age groups without altering the maximum tension. Additionally, in endothelium-intact preparations, increasing age from 4 to 24 month s decreased the sensitivity to norepinephrine. Exposure to 2.4 vol.% h alothane caused a significant decline in the maximum tension generated in response to norepinephrine in all groups. There were no difference s in the amount of depression seen with 2.4 vol.% halothane either wit hin age groups or between endothelium-intact and -denuded preparations of the same age. Halothane at 1.2 vol.% caused a significant reductio n in the amount of tension generated in the 4-month-old, endothelium-d enuded group. However, all age groups with and without endothelium ten ded to decrease to a similar degree at 1.2 vol.% halothane, and there were no differences either within age groups or between endothelium-in tact and -denuded preparations of the same age. In the 4- and 14-month -old endothelium-intact groups, both 1.2 and 2.4 vol.% halothane decre ased the sensitivity to norepinephrine. If this model of aging is pred ictive of general vascular responsiveness in other species, these data suggest that the increased cardiovascular depression elicited by halo thane in elderly individuals is not mediated by an enhanced susceptibi lity to the direct vascular effects of the anesthetic.