Ovarian Secretion of Pregnane Compounds During the Estrous Cycle and Pregnancy in Rats

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Abstract
The amounts of progesterone, 5α-pregnane-3,20-dione, 3α-hydroxy-5α-pregnan-20-one, 20α-hydroxypregn-4-en-3-one, 20α-hydroxy-5α-pregnan-3-one and 5α-pregnane-3α,20α-diol in ovarian venous plasma at selected stages during the estrous cycle and pregnancy in rats, were determined by gas chromatography. Progesterone showed peak levels at late proestrus and at early diestrus. The former peak was associated with an increase in 5α-pregnane-3,20-dione and 3α-hydroxy-5α-pregnan-20-one, suggesting that the peak was due to LH stimulation. LH (2 µg) administered intravenously 30 min before sample collection increased the secretion of 20-keto-pregnane compounds at proestrus and at early and late diestrus. In addition, progesterone levels during pregnancy showed two peaks; a small peak on days 3 to 5 and a larger peak on days 13 to 20 of pregnancy. A minimal level was observed on days 7 to 10 of pregnancy. LH increased the progesterone level on day 7 of pregnancy but had no effect on the level at day 10. The concentrations of 20α-OH and 5α-pregnane compounds were higher during the estrous cycle, decreased to low levels by day 5 of pregnancy and remained depressed until term. A significant increase in the level of the 20α-OH pregnene compound occurred immediately after delivery. The secretion of 5α-pregnane-3,20-dione and 3α-hydroxy-5α-pregnan-20-one increased throughout all stages of pregnancy following LH stimulation. The ability of the ovary to secrete 5α-pregnane compounds on LH stimulation was greatest during the estrous cycle, and became less responsive with the duration of pregnancy. They remained at a high level at days 3 to 5 of pregnancy and decreased to a low level after day 10 of pregnancy. (Endocrinology94: 1615, 1974)

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