Effects of general anesthetics on plasma levels of catechols in intact and in adrenal-demedullated rats

Experiments about sympathetic nervous system function in stress and disease often have included measurements of plasma levels of catecholamines in anesthetized animals. Different general anesthetics can produce different sympathoadrenomedullary responses. We examined effects of commonly used general anesthetics on plasma levels of catechols in intact and in adrenal-demedullated rats. In intact rats, exposure to diethyl ether produced acute increase in arterial plasma levels of epinephrine (EPI) and smaller increases in levels of norepinephrine (NE) and dihydroxyphenylglycol (DHPG), the main intraneuronal metabolite of NE. Pentobarbital injection decreased levels of NE, EPI, DHPG and dihydroxyphenylalanine (DOPA), the precursor of the catecholamines. Administration of ketamine or urethane increased levels of NE and EPI transiently. Chloralose decreased EPI levels in intact animals and NE levels in adrenal-demedullated rats, whereas halothane did not affect plasma levels of catechols in intact animals. Adrenal demedullation augmented the increases in levels of NE in response to ether or ketamine and the decrease in NE in response to pentobarbital or chloralose. The results demonstrate that levels of catechols can be affected differentially depending on the type of anesthetic, the time since drug administration and the presence of functioning adrenal medullary tissue. The results also are consistent with a compensatory interaction between the sympathoneural and adrenomedullary components of the sympathoadrenal system.