Etomidate inhibits prolactin release but not through a dopaminergic mechanism

Adrenocortical suppression and other endocrine effects of etomidate

(+/-) Etomidate is a short-acting general anaesthetic given by the intravenous route. It has strong adrenal suppression capability initially shown in the rat and then observed in man. At present, the drug seems the most effective adrenocortical inhibitor on a molar basis in vitro. 11 beta-hydroxylase is the most sensitive target enzyme; 16 alpha-, 17 alpha-hydroxylase and cholesterol side-chain cleavage are inhibited by higher concentrations. (+) Etomidate was more active than the (+/-) and far more than the (-) stereoisomer. Etomidate blood concentrations greatly exceed those needed to block adrenal steroidogenesis both when used inappropriately by infusion for long-term sedation (such previously unrecognized drug-induced adrenal suppression has often proved fatal in severely-injured patients) and also when given in very low doses as an induction anaesthetic. Reactive ACTH increase is currently observed. Etomidate, in vivo, does not appear to affect testicular steroidogenesis although it shares an imidazole moiety with fungicide phenylimidazoles endowed with such an action. However, testosterone production may be reduced by high concentrations in vitro. Other gonadal hormones seem unchanged. Both basal and stress-induced blood prolactin levels are lowered by etomidate in the rat but probably not in man arguably through interference at brain level where the GABA-benzodiazepine receptor complex could be directly involved. Hence, endocrine and neuroendocrine interferences are unique non-anaesthetic effects of etomidate.

Electrophysiological studies of the effects of the general anaesthetic etomidate on frog myelinated nerve fibre

The effects of the general anaesthetic etomidate (0.1 to 1 mM) upon the node of Ranvier of frog isolated nerve fibres were investigated under current and voltage clamp conditions. When added to the external solution, etomidate reversibly decreased the amplitude of the action potential. The action potential block, induced by the drug, was reversed by increasing the membrane potential. Etomidate rapidly and reversibly blocked the Na current with an apparent dissociation constant of 0.6 mM. In the presence of the drug, the steady-state inactivation-voltage curve of the Na current was shifted towards negative voltages. The block of Na current by etomidate was partially removed by repetitive depolarization preceded by a 50 ms period of hyperpolarization. In contrast, the block was enhanced when the repetitive depolarization was not preceded by hyperpolarization. This suggests that Na channels were preferentially blocked by the drug in the inactivated state. The K current was reversibly blocked by etomidate with an apparent dissociation constant of 0.2 mM. In the presence of the drug, the K current showed an apparent fast inactivation suggesting that K channels were blocked in the open state. We conclude that at higher concentrations than those attainable in the mammalian brain following single anaesthetic doses the general anaesthetic etomidate has a "local anaesthetic-like' action on the peripheral nervous system.