OBJECTIVE: This study was undertaken to investigate the effects of the polyamine spermine on human uterine contractility.STUDY DESIGN: Under physiologic conditions, an isometric tension recording was performed in isolated myometrial strips from biopsy specimens obtained at elective cesarean delivery (n = 24 specimens) and from premenopausal hysterectomy specimens (n = 6 specimens). The effects of spermine (1 mumol/L-10 mmol/L in cumulative doses) on spontaneous, agonist-induced myometrial contractions were measured, and dose response curves were constructed. The pD(2) (-log EC50) values and the maximal inhibition values achieved were compared for spontaneous and agonist-induced contractions.RESULTS: Spermine exerted a potent relaxant effect on all spontaneous and agonist-induced myometrial contractions, with mean maximal inhibition values between 62.8% +/- 4.3% and 91.4% +/- 1.8% and pD(2) values between 2.66 +/- 0.23 and 4.01 +/- 0.20. Its inhibitory effect varied significantly with different contraction types (pD(2), P <.05; mean maximal inhibition, P <.001), and it was least potent on BAY K 8644-elicited contractions (pD2, P <.05; mean maximal inhibition, P <.01).CONCLUSION: The polyamine spermine exerts a potent relaxant effect on human uterine tissue, This effect appears to be mediated, at least partially, by calcium antagonism. Polyamines may play a role in the maintenance of uterine quiescence during pregnancy.