Efferent vagal discharge and heart rate in response to methohexitone, althesin, ketamine and etomidate in cats.

The effects of methohexitone, Althesin, ketamine and etomidate on single fibre discharge of cardiac vagal efferents and on heart rate were studied in cats. Cardiac vagal efferents were inhibited markedly and regularly for equihypnotic doses of methohexitone (2.0 mg kg-1), Althesin (0.1 ml kg-1) and ketamine (5.0 mg kg-1), but not of etomidate (0.8 mg kg-1). These inhibitory effects were independent of arterial pressure and mirrored the increases of heart rate elicited by the first three agents. Etomidate did not consistently affect cardiac vagal discharge or heart rate. Thus methohexitone. Althesin and ketamine inhibit efferent cardiac vagal drive by their central action independently of baroreflex function. This central vagolysis is probably the cause of their positive chronotropic effects.