Anisomycin and verapamil influence the action of progesterone on regulation of term human myometrial contractile activity.

OBJECTIVE

Progesterone has been shown to have both stimulatory and inhibitory effects on term human myometrial contractile activity. The mechanisms involved in this action of progesterone are still poorly understood.

DESIGN

Myometrial tissues were obtained from the lower uterine segment at elective Caesarean section of 30 term pregnant women. The contractile activity of muscle strips was measured by a superfusion technique and protein synthesis evaluated by [3H]-leucine incorporation.

RESULTS

[3H]-leucine incorporation into term myometrial strips was not affected by progesterone (10 mumol/l), but was markedly reduced by the protein synthesis inhibitor anisomycin (P < 0.05). However, progesterone increased frequency and tonus of contractions and reduced the activity-area of contractions (P < 0.01). Anisomycin (100 mumol/l) did not change these effects or the spontaneous contractile activity. Removal or extracellular Ca2+ or addition of the L-type calcium channel blocker verapamil prevented the spontaneous as well as the progesterone-induced contractions, but had less pronounced effects on contractions initiated by oxytocin.

CONCLUSION

The results indicate that the actions of progesterone on term myometrial contractile activity occur without protein synthesis and that increased Ca2+ influx or decreased outward transport of Ca2+ may play a possible role)