Direct Luteotropic Action of Estrogen in the Hypophysectomized-Hysterectomized Rat

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Abstract
Rats hypophysectomized (Hx) on day 12 of pregnancy had plasma and luteal levels of. progesterone on days 16 and 20 comparable to intact controls. Progesterone levels were also unaffected by fetectomy at day 16 (with placentae left in situ). However, hysterectomy (Hs) at day 12 led to a precipitous decline in progesterone by day 16 and low plateau values were maintained through day 20. The combined effects of Hx and Hs at day 12 were even more drastic in curtailing progesterone synthesis by day 20. Thus, the corpora lutea of the second half of pregnancy were not autonomous, requiring continuous hormonal support for the maintenance of progesterone levels. The effects of Hx and Hs at day 12 were not reversible by prolactin (PRL) or FSH or LH or the combination of these hormones. However, large daily doses of estrone (10 μg) or single or daily doses of estradiol cyclopentylpropionate (25 μg) restored luteal and plasma levels of progesterone to values of intact day 16 pregnant rats. These results in hypophysectomized—hysterectomized rats suggest a direct luteotropic action of estrogen in the second half of pregnancy. They may also account for the failure of an anti—LH serum to interrupt pregnancy in the second half of gestation in the rat (1). Combined daily injection of PRL and estrogen, over the dosage range tested, failed to show any synergistic interaction. (Endocrinology92: 1405, 1973)

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