Progesterone in Ovarian Venous Plasma and Corpora Lutea of the Pig1

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Abstract
Ovarian venous blood and luteal tissue from one ovary were obtained at days, 1, 4, 8, 12,14, 16 and 18 of the estrous cycle. Pigs were hysterectomized at days 5-7, and blood and luteal tissue were collected at days 14, 18 and 25. Similar samples were obtained during early pregnancy, days 14, 18 and 25 and late pregnancy, days 102,110 and 112. Plasma progesterone levels increased from day 1 to day 8 and declined thereafter to day 18. Either the presence of embryos in the uterus or the absence of the uterus caused increased progesterone production as early as the 14 day, when compared with the same day of the estrous cycle. Plasma progesterone levels were reduced even though corpora lutea were large during late pregnancy. There was a linear relationship between the logarithm of the concentration of progesterone in the ovarian venous blood and the content of this steroid in the luteal tissue during the estrous cycle.