Does sildenafil citrate affect myometrial contractile response to nifedipine in vitro?

OBJECTIVE

We sought to test the hypothesis that sildenafil citrate (SC) at low concentrations potentiates the tocolytic effects of nifedipine in vitro.

STUDY

DESIGN

Myometrial biopsies were obtained from 22 term nonlaboring women undergoing scheduled cesarean delivery. Tissue strips were suspended in organ chambers for isometric tension recording, and incubated for 30 minutes with either SC at 231 ng/mL or solvent. The effects of cumulative doses (10(-10) to 10(-5) mol/L) of nifedipine on spontaneous and oxytocin-induced uterine contractility were then determined. Areas under the contraction curve were compared using 1-way analysis of variance with Tukey post hoc test (significance: P < .05).

RESULTS

Nifedipine significantly inhibited spontaneous and oxytocin-induced myometrial contractility. Preincubation with SC increased response to nifedipine and significantly potentiated its inhibitory effect at 10(-8) mol/L, without affecting oxytocin-induced contractile response.

CONCLUSION

At concentrations within a therapeutic window, SC increases myometrial sensitivity to nifedipine.