Nathanielsz P W, Buster J E, Jenkin G, Jorgensen G, Thorburn G D
Cornell University, New York State College of Veterinary Medicine, Ithaca 14853.
J Dev Physiol. 1988 Jun;10(3):257-70.
Infusion of cortisol to the fetus of late pregnant sheep caused an increase in maternal and fetal plasma oestrone and oestrone sulphate concentration and subsequent delivery of the fetus. Administration of progesterone or medroxyprogesterone acetate to late pregnant sheep inhibited the induction of labour. The changes in maternal and fetal plasma concentrations of pregnenolone, 17 alpha-hydroxypregnenolone, dehydro-epiandrosterone and their respective sulphates were not significantly altered by the administration of progestagens during induction of delivery. Placental delta 5-3 beta-hydroxysteroid dehydrogenase was not, therefore, significantly inhibited by progestagen administration. Furthermore induction of 17 alpha-hydroxylase and C17-20 lyase by cortisol was not suppressed. Similarly, since the changes in maternal and fetal oestrone and oestrone sulphate concentrations were not affected by treatment of the ewe with either progesterone or medroxyprogesterone acetate, the increase in the activity of aromatase, observed during induced parturition, was not inhibited, not did the exogenous progesterone provide any further substrate for placental oestrogen production. Progestagen treatment is, however, able to inhibit delivery when administered in sufficient quantities to overcome the stimulatory effect of the oestrogens produced by the placenta from endogenous precursors.
向妊娠晚期绵羊的胎儿输注皮质醇会导致母体和胎儿血浆雌酮及硫酸雌酮浓度升高，并随后使胎儿分娩。向妊娠晚期绵羊施用孕酮或醋酸甲羟孕酮可抑制分娩诱导。在诱导分娩期间施用孕激素，母体和胎儿血浆中孕烯醇酮、17α-羟孕烯醇酮、脱氢表雄酮及其各自硫酸盐的浓度变化未受到显著影响。因此，施用孕激素不会显著抑制胎盘Δ5-3β-羟基类固醇脱氢酶。此外，皮质醇对17α-羟化酶和C17-20裂解酶的诱导作用未被抑制。同样，由于母体和胎儿雌酮及硫酸雌酮浓度的变化不受用孕酮或醋酸甲羟孕酮处理母羊的影响，因此在诱导分娩期间观察到的芳香化酶活性增加未被抑制，外源性孕酮也未为胎盘雌激素生成提供任何额外底物。然而，当施用足够量的孕激素以克服胎盘从内源性前体产生的雌激素的刺激作用时，孕激素治疗能够抑制分娩。
