Bacitracin U.S.P. contains a factor that stimulates receptors for 5-hydroxytryptamine on rabbit aortic strips

Bacitracin (BAC) U.S.P., obtained in the form of sterile powder, elicits dose-dependent and non-tachyphylactic contractions of the rabbit isolated aorta and of other rabbit vessels. The use of several pharmacologic antagonists suggests that BAC is a 5-hydroxytryptamine mimetic in aortic strips, since the antibiotic is competitively antagonized by methysergide and ketanserin with pA2 values compatible with an agonist action on the 5-HT2 receptors found in the aortic preparation. It remains to be determined whether bacitracin A, the chief constituent of BAC U.S.P., is the 5-HT agonist.