INHIBITION OF 3-HYDROXYSTEROID DEHYDROGENASE IN THE SOW NEAR TERM: EFFECTS ON FETAL AND MATERNAL STEROIDS AND ON DELIVERY

¹ The Physiological Laboratory, Cambridge CB2 3EG

The effect of Epostane, a 3-hydroxysteroid dehydrogenase inhibitor, on maternal and fetal plasma progesterone and other steroids has been investigated in chronically catheterized pregnant sows near term. Epostane (1-2 mg/kg) was given I.V. and samples withdrawn from the uterine vein and artery and a fetal artery. In seven sows tested at 106-110 d gestation (term 115 d) Epostane induced parturition 25 ± 2·1 h later with the birth of live viable young (group 1). In four sows tested with the same dose of Epostane at 106-111 d gestation parturition was not induced (group 2). A rapid drop in maternal and fetal plasma progesterone occurred after Epostane; in group 1 maternal progesterone remained below 4 ng/ml until delivery whereas in group 2 the drop was temporary, as was the decrease in fetal progesterone in all animals. Epostane also resulted in a rapid fall in maternal and fetal plasma cortisol with a gradual recovery over the following 9-12 h which was accompanied by increased ACTH (adreno-corticotrophic hormone) levels in the fetus. In group 1 fetuses a further escalation in both cortisol and ACTH occurred up to and during delivery while in group 2 basal concentrations were restored after 24 h. Epostane also reduced maternal oestrone concentrations in both groups over the 6-9 h after drug treatment. In group 2 the basal oestrone concentrations and the oestrone/progesterone ratio before and after Epostane administration were lower than in group 1 which may in part explain the failure of Epostane to induce labour in the former despite their similar gestational age. It is concluded that Epostane is not a reliable inducing agent in the sow when infused within 5-10 d of term although enhanced adrenocortical activity probably ensures the viability of the piglets if delivered.