Corpus Luteum-Pituitary Relationship: The Effect of Progesterone on the Folliculotropic Potency of the Pituitary in the Rat

Abstract

In order to determine whether progestorone suppressed formation or release of pituitary folliculotropins (FSH and LH, abbreviated as FTH), the pituitaries of cycling and of pseudopregnant rats were assayed for FTH potency by the mouse uterine weight method and compared with those of cycling rats treated with progesterone. The effect of progesterone on the pituitary of the castrated rat was similarly studied. The pituitaries from the various groups were pooled, dried and injected into assay mice at from 4 to 7 different doses per run. The pituitaries of cycling rats doubled mouse uterine weight at a dose of approximately 0.6 mg, while the pituitaries of pseudopregnant rats (7th or 12th diestrus day) did so at a dose of approximately 0.3 mg. The pituitaries of cycling rats treated with either 5.0 or 10.0 mg of progesterone/day for 14 days were in the same potency range as those of pseudopregnant rats. The pituitaries of rats treated with 1.0 mg of progesterone were slightly more potent than those of untreated rats; the pituitaries from rats treated with 0.1 mg were indistinguishable from those of untreated control rats. Castrates treated with 5.0 or 10.0 mg of progesterone for 14 days showed no depression of the typical postcastration increase in pituitary FTH potency and may have shown a further, but small increase. Together with the fact that, although the ovary of the pseudopregnant rat shows follicular quiescence it responds to FTH stimulation (3), these findings were interpreted as evidence that progesterone inhibits only the release of folliculotropins and but not their formation.