OBJECTIVE: Polyamines act as endogenous modulators of cell function and excitability. There are no data in relation to their effects on the human fetoplacental circulation. The aim of this study was to investigate the effects of the polyamines, spermine, and spermidine on human umbilical artery resistance in vitro.METHODS: Isometric tension recordings were performed under physiologic conditions on human umbilical arterial rings (n = 12). The in vitro effects of spermine and spermidine (at concentrations ranging between 10(-9) M to 10(-3) M) were measured, and compared with those measured in vehicle control experiments. The maximal inhibition (MMI) at the highest concentration and the pD(2) (-log EC50) values for each compound were calculated and compared.RESULTS: Spermine and spermidine exerted a potent relaxant effect on human umbilical arterial tone in fir spermine was 18.41 +/- 1.437 % comparison to vehicle control experiments. The MMI +/- SEM (n = 6; P < .001) and for spermidine was 38.31 +/- 3.572 % (n = 6; P < .001). There was no difference observed between the pD(2) +/- SEM values for spermine (5.78 +/- 1.54; n = 6) and spermidine (6.27 +/- 0.85; n = 6) (P = .517).CONCLUSION: The polyamines spermine and spermidine exert a potent relaxant effect on human umbilical artery tone suggestive of an endogenous role fir these compounds in vasomotor regulation of the fetoplacental circulation. Copyright (C) 2004 by the Society for Gynecologic Investigation.