Preovulatory Progestins: Observations on Their Source in Rhesus Monkeys1

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Abstract
Progesterone (P) and 20alpha-hydroxypregen-4-en-3-one (20alpha-ol)concentrations were measured in systemic and ovarian vein plasma of adult cycling female rehsus monkeys by gas liquid chromatography with electron capture detection. Blood samples and ovaries were removed at various times during the intermenstrual period. The animals were then reclassified according to the stage of the ovarian cycle and the morphology of the ovary. Very little P or 20alpha-ol is secreted by the ovary during the follicular phase until the largest developing follicle measures 5.6 mm in diameter. In the prevular period, the concentrations of both P and 20alpha-ol in the two ovarian veins are nearly equal. As the luteal phase develops, the ratios of progestin concentrations in the ovarian vein change, more progestin being found in ovarian venous plasma of the ovary with the corpus luteum. The secretion of preovulatory progestin can be correlated with large amounts of interstitial gland cells that appear before ovulation in the ovary. In a second experiment, follicular development was estimated by a rapid radioimmunoassay for estrogen in the systemic circulation. When the systemic plasma levels of immunoreactive estrogen exceeded 150 pg/ml, ovarian venous samples of blood were collected from each ovary and analyzed by radioimmunoassay for estradiol-17beta and progesterone. Ffteen min after removal of the ovary that contained the mature Graafian follicle, blood was drawn from the contralateral ovarian vein. In this preovulatory condition, the progesterone concentrations in both ovarian veins greatly exceeded those in the systemic circulation. In 2 animals, removal of the ovary that contained the mature Graafian follicle did not lower the blood levels of progesterone in the contralateral ovarian vein after 15 min. These data suggest that both ovaries of the rhesus monkey secrete preovulatory progestin which is available for physiological action.

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