THE CORPUS LUTEUM-HYPOPHYSIS RELATIONSHIP.

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Abstract
The corpora lutea of pseudopregnant rats reached their approximate maximum size by 14 days, and were in well advanced regression by 28 days, after ovulation. Progesterone treatment (2, 5 or 10 mg/day) did not affect luteal growth, and progesterone treatment, either alone or combined with hypophyseal homotransplantation, did not prevent luteal regression. In hypophysectomized rats bearing hypophyseal autotransplants, however, progesterone treatment was not associated with luteal regression. In the progesterone-treated intact pseudopregnant rats, the maintenance of follicle growth, the presence of vaginal mucification, and the maintenance of hypophyseal LH potency at a level equivalent to that of cyclic rats at prooestrus, indicated that at least a basal rate of LH secretion was probably maintained. Treatment of pseudopregnant rats with 5 μg oestradiol/day for 28 days reduced the incidence of luteal regression only to 69 %, and with 20 μg/day to 60 %, although treatment with 50 μg/day reduced it to 11 %. Pseudopregnant rats, bearing one or two hypophyseal homotransplants, treated for 28 days with oestradiol (5 μg/day), showed a partial (one transplant) or complete (two transplants) maintenance of luteal growth. There was a direct relationship between luteal size and the duration of dioestrus. LH secretion, as judged by the growth of follicles, and hypophyseal LH potency, was markedly depressed by oestradiol (5 μg/day) treatment. The combination of oestradiol (5 μg/day) with progesterone (2, 5, or 10 mg/day) treatment for 28 days maintained luteal growth in almost 100 % of the rats (30/31 rats). LH secretion was apparently depressed as much as with oestradiol treatment alone. LH treatment (5 μg/day or more) of oestradiol-progesterone treated rats induced luteal regression uniformly. The combined hormone treatment did not maintain luteal growth in hypophysectomized rats. The extent to which these results support the possibility that progesterone can maintain LTH secretion was discussed.