Effect of general anesthetics on handling- and decapitation-induced increases in sympathoadrenal discharge.

The effect of five anesthetics--cyclopropane, pentobarbital, urethane, chloralose or ketamine hydrochloride--on handling- or decapitation-induced increases in adrenergic tone were studied in the intact rat. The anesthetic agents tested prevented or markedly reduced stress-induced increases in levels of plasma total catecholamines and norepinephrine. Similar changes in norepinephrine were seen in corticosterone- treated adrenalectomized rats in which this catecholamine seemed to be the only one present in plasma. During anesthesia with cyclopropane, blood pressure fell; there was no additional decrease in total plasma catecholamines when the concentration of the inhaled anesthetic agent was increased. With increased length of cyclopropane anesthesia, however, total catecholamine and norepinephrine concentrations increased. Thus, the different effects of anesthetics on the cardiovascular system cannot be solely explained by their effects on stress-induced increases in sympathetic neuronal activity as reflected by circulating catecholamine levels.