The adrenal cortex and the luteotrophic action of estrogens during the estrous cycle in the rat.

The aim of this study was to evaluate the effects of estradiol benzoate (EB) on ovarian progesterone secretion in the presence or in the absence of the adrenals. 4-day cyclic female rats were injected with 10 microgram EB on the morning of diestrus I. An increase in the rate of ovarian progesterone secretion in diestrus II at either 10--11 a.m. or at 2 : 30--3 : 30 p.m. was only observed in one of two experimental series. A very significant increase in the peripheral blood progesterone concentration was noted in adrenalectomized EB-treated females as compared to EB-injected intact females, thus suggesting that the adrenals might inhibit the luteotrophic action exerted by EB on the ovary. Experiments in dexamethasone (DEX)-EB-treated females confirmed this view. Peripheral blood progesterone concentration was significantly greater in DEX-EB-treated females than in EB-treated females. The possible mechanisms were discussed in the light of experiments involving the administration of metyrapone (MET) prior to EB injection. While blood progesterone concentration increased following MET-treatment only, no cumulative effects resulted from combined MET and EB-treatment. Progesterone of adrenal origin was then supposed to be implicated in the inhibitory action of the adrenal cortex on the luteotrophic action of EB in cyclic female rats.