Effects of ergosterol and adrenalectomy on the maintenance of pregnancy in the ovariectomized rat

1. 1. Groups of five or six rats ovariectomized at day 9 of pregnancy were injected daily with 1.2, 2.6 or 4.0 mg progesterone with or without 10 mg ergosterol. 2. 2. Ergosterol had a significant progesterone-sparing action expressed particularly by an increase in the number of live foetuses carried to day 19 of pregnancy and this effect was most marked in the animals given 2.6 mg progesterone. 3. 3. In a second experiment groups of rats were ovariectomized on day 9 of pregnancy: half of these rats were adrenalectomized as well and given saline to drink thereafter. All animals were maintained on daily injections of 3 mg progesterone and half of each group were given 10 mg ergosterol/day in addition. 4. 4. Ergosterol improved reproductive performance in the non-adrenalectomized but not in the adrenalectomized group and adrenalectomy itself increased the numbers of foetuses that survived ovariectomy. 5. 5. It is suggested that the progesterone-sparing action of ergosterol and of adrenalectomy may both be brought about by increasing the proportion of progesterone bound to specific transport-proteins in the plasma, thus protecting it from hepatic metabolism.