Effects of histaminergic drugs on the contractile activity of smooth muscles from imipramine-treated rats.

The effects of histaminergic drugs and their interaction with adrenergic neurotransmission in smooth muscles from imipramine-treated animals were studied. The experiments were performed on isolated preparations (vasa deferentia and segments from terminal ileum and proximal colon) from male Wistar rats which were given imipramine, 10 mg/kg orally, twice daily for 2 weeks. The effects of histamine (HIST) and diphenhydramine (DPH) on the tone and phasic contractions of ileum and colon were investigated. The action of the histaminergic drugs on the vas deferens contractions evoked by low-frequency electrical stimulation (LFES) was also studied. In imipramine-treated animals LFES elicited much stronger contractions than in the controls. HIST modulatory action on the LFES-induced contractions was not markedly changed. The potentiation of the vas deferens contractions by DPH was strongly decreased. Imipramine reduced the potentiating action of both histaminergic agents on the ileum phasic contractions as well as the enhanced effects of HIST applied 10 min after DPH. Imipramine had opposite effects on the potentiating action of HIST and DPH on the colon phasic contractions: the HIST effects were slightly reduced and those of DPH were enhanced. After H1-blockade HIST exerted a stronger potentiation of the colon spontaneous contractions as compared to the controls. Present data show that imipramine could change the modifying action of histaminergic agents on adrenergic neurotransmission and also their interaction with histaminergic receptors in smooth muscles.