Effect of histamine on phasic and tonic contractions of isolated uterine tissue from pregnant women

OBJECTIVE: To enhance our understanding of the uterotonic effect of histamine, we compared the effects of histamine on spontaneous phasic and tonic contractile activity of uterine strips from term pregnant nonlaboring women. STUDY DESIGN: Longitudinal uterine strips were used from the lower uterine segment of term pregnant nonlaboring women undergoing elective cesarean. section. The concentration-response relationship to histamine (10(-8) to 10(-4) mol/L) was determined in spontaneously contracting strips or in strips contracted tonically witha protein kinase C activator (-)-indolactam V in the presence of H-1 receptor antagonist (S[+]-chlorpheniramine maleate), H-2 receptor antagonist (cimetidine), or solvent. RESULTS: Histamine increased spontaneous phasic myometrial contractions in a concentration-dependent manner. H-1, but not H-2, receptor antagonist significantly attenuated the response to histamine. Histamine significantly reduced tonic contractions of uterine strips induced by indolactam V. H histamine receptor antagonist abolished relaxation, whereas H-2 histamine receptor antagonist had no effect. CONCLUSION: Histamine increases spontaneous, but inhibits tonic, contractions of uterine strips from term pregnant nonlaboring women. Both effects are mediated through activation of H-1 receptors.