Effects of nitric oxide donors on the contractility and prostaglandin synthesis of myometrial strips from pregnant and non-pregnant women

Nitric oxide (NO) is a potent relaxant of smooth muscle and possibly plays a role in maintaining uterine quiescence during pregnancy. Clinical studies have shown beneficial effects of the stable NO donor glyceryl trinitrate ( GTN) for the inhibition of pathological myometrial contractility that occur s in preterm labor or dysmenorrhea. Since there are contradictory results r egarding the mediation of the relaxing effect of NO, the myometrial prostag landin synthesis during superfusion with NO donors was studied. Human myometrial strips obtained either at term Cesarean sections before th e onset of labor or after hysterectomies in premenopausal women were studie d in a superfusion system. After the manifestation of spontaneous contracti ons, GTN was added in low doses comparable with in vivo levels (0.4-40 nM) and the effect on myometrial activity, intracellular cGMP and prostaglandin production was analyzed. Additionally, the effect of sodium nitroprusside (SNP)- which releases NO spontaneously - was compared with that of GTN. GTN caused a significant decrease in the contraction frequency of myometria l strips from both pregnant and non-pregnant women similar to that of SNP. There was no significant change in the myometrial synthesis of PGI(2), PGF( 2 alpha) and PGE(2), whereas the intracellular cGMP content was increased. In conclusion, GTN showed a significant inhibitory effect on human myometri um in vitro in very low doses and therefore represents an interesting thera peutic alternative for the treatment of preterm labor and dysmenorrhea. GTN in low noses did not alter the prostaglandin synthesis of human myometrium .