Refractoriness of the gravid rat uterus to tocolytic and biochemical effects of atrial natriuretic peptide.
1. Effects of atrial natriuretic peptide (ANP) on tension development, particulate guanylate cyclase activity and guanosine 3':5'-cyclic monophosphate (cyclic GMP) concentrations of uteri from oestrogen-treated, progesterone-treated, ovariectomized and pregnant rats were determined in vitro. 2. ANP inhibited the tension development by myometrial tissues from oestrogen-treated virgin rats and the sterile horn of 10 to 14 day pregnant rats but not of the uterus from pregnant and progesterone-treated rats. 3. Inhibition of cyclo-oxygenase and lipoxygenase activities did not restore the tocolytic activity of ANP on gravid uterus. ANP exerted a tocolytic effect on nongravid uterus submaximally stimulated by prostaglandin F2 alpha (PGF2 alpha), oxytocin, vasopressin, angiotensin II or 5-hydroxytryptamine (5-HT). 4. Ovariectomy decreased the tocolytic effects of ANP, which could be restored by oestrogen treatment. 5. The refractoriness to the tocolytic effect of ANP in pregnant rats was not accompanied by a decrease in its relaxant effects on isolated aortic strips. 6. Tocolytic effects of isoprenaline, isobutylmethyl xanthine and hydroxylamine were not influenced by pregnancy or progesterone treatment. Up to a concentration of 3 mM, sodium nitroprusside did not affect myometrial tension development. 7. Pregnancy and progesterone treatment markedly inhibited ANP-induced increases in myometrial particulate guanylate cyclase activity and cyclic GMP concentrations but did not influence the effects of ANP on aortic cyclic GMP concentrations. 8. It is concluded that exposure of the myometrium to circulating and placentally-produced progesterone is responsible for the pregnancy-induced decrease in the effects of ANP on myometrial particulate guanylate cyclase activity and cyclic GMP concentrations and in turn on myometrial tension development.
Potvin
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Department of Pharmacology & Therapeutics, McGill University, Montreal, Canada.
Varma
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D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects; D009320:Atrial Natriuretic Factor / Q000494:pharmacology*; D006152:Cyclic GMP / Q000096:biosynthesis / Q000378:metabolism; D016861:Cyclooxygenase Inhibitors; D005260:Female; D006162:Guanylate Cyclase / Q000378:metabolism; D016859:Lipoxygenase Inhibitors; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009215:Myometrium / Q000187:drug effects; D009431:Neural Conduction / Q000187:drug effects*; D010052:Ovariectomy; D011247:Pregnancy; D011374:Progesterone / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012032:Refractory Period, Electrophysiological / Q000187:drug effects*; D015149:Tocolytic Agents; D014590:Uterine Contraction / Q000187:drug effects; D014599:Uterus / Q000187:drug effects* / Q000378:metabolism
D016861:Cyclooxygenase Inhibitors; D016859:Lipoxygenase Inhibitors; D015149:Tocolytic Agents; D011374:Progesterone; D009320:Atrial Natriuretic Factor; D006162:Guanylate Cyclase; D006152:Cyclic GMP