Contractor effect of barbiturates on smooth muscle.

Four different convulsant barbiturates and also thiopental, methohexital and pentobarbital were tested for in vitro contractor effects on rabbit jejunal segments, aortic strips and tracheal chains. The two convulsants that elicited lethal, tonic seizures in vivo contracted all three types of isolated preparation; however, two other convulsants that elicited intense but nonlethal, clonic seizures lacked contractor effect. Methohexital and pentobarbital also lacked contractor effect. In aortic strips, contractions induced by the two convulsants were not impaired by concentrations of phenoxybenzamine (10(-5) M) that blocked all contractor response to 10(-4) M norepinephrine, acetylcholine or histamine. Thiopental also contracted aortic strips but the effect differed from that of the convulsants in that it was much less intense, was partially antagonized by pretreatment with phenoxybenzamine, and was greatly potentiated by the presence of norepinephrine. Intense contractor effects, independent of adrenergic mechanisms, seem characteristic of a particular group of convulsant barbiturates; there are also similar with respect to structure, stimulant potency, and seizure pattern.