Pharmacological effects of althesin and its steroidal components on the cardiovascular system.

Althesin and its two steroidal components elicited, despite a deficit vasopressor effect by their solvent vehicle Cremophor El, a well-marked hypotensive activity appearing abruptly after i.v. injection in chloralosed cats. This vasodepressor effect which was weaker and shorter lasting with alphadolone acetate than alphaxalone proved to be one-cholinergic, nonhistaminergic, not mediated via any ganglionic blocking activity and ;mostly attributable to central depressant action on vasomotor tone. An appreciable direct myocardial inhibition and a much weaker direct peripheral vasodilatation were shown to be contributory factors to the hypotension. ECG studies in chloralosed cats indicated the occurrence of mild grade bradycardia or else no evident change in the heart rate under the influence of althesin and its steroidal components. A definite protective influence for althesin mainly due to alphaxalone against adrenaline induced arrhythmia in chloralosed cats was also demonstrated.