Plasma Progesterone Levels in The Pregnant Mare’s Serum (PMS)-Treated Immature Female Rat

Immature rats pretreated with PMS (pregnant mares serum) were studied to determine whether progesterone was present in sufficient amounts and at such a time as to play a role in the release of LH (luteinizing hormone). From no progesterone at PMS injection serum progesterone levels rose to 5.88 plus or minus .28 nonograms per ml. by 56 hours after PMS injection. Ovariectomized and hypophysectomized rats showed undectable and .7 nanograms per ml progesterone respectively following PMS treatment. Progesterone may be one of the signals for the release of LH. The source of progesterone in the immature rat seems to be the ovary and progesterone was secreted by the ovary prior to the formation of the corpora lutea.