Abstract
Summary
The threshold of progesterone required for maintenance of diestrus smear, pseudopregnancy and pregnancy in ovariectomized rats has been shown to differ significantly. Whereas, vaginal diestrus can be maintained in ovariectomized rats, in the face of constant estradiol challenge, with as little as 50–100 μg of progesterone, the amounts needed for induction of decidualization and maintenance of early pregnancy are respectively 250 μg and 3 mg. In pregnancy itself, the progesterone need continuously varies, from a high of 3–4 mg of progesterone/day during the first 12 days to as little as 250 μg during the last 5 days of gestation. This differential threshold for progesterone may perhaps be responsible for the observed luteotropic activity of prolactin and LH in varying physiological situations.
The authors wish to express their sincere thanks to Messers. B. Shanmugavelu and P. Pasu Pathy for skilled technical assistance. The authors were aided by grants from the Ministry of Health and Family Planning, Government of India, and the Ford Foundation, New York.
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