Effect of Progesterone on the Level of Plasma Luteinizing Hormone (LH) in Normal Female Rats

Plasma LH was determined in normal female rats at various stages of the estrous cycle and in ovariectomized rats by the ovarian ascorbic acid depletion assay. Plasma LH was elevated at proestrus during the normal cycle and in ovariectomized animals. Single subcutaneous (sc) injections of progesterone in oil elevated plasma LH on measurement 6 hr later when the injections were given in late diestrus or in proestrus during the normal cycle. Progesterone failed to alter plasma LH activity during estrus and in early diestrus and also was without effect on plasma LH in ovariectomized rats. It is concluded that progesterone stimulates LH release when administered during the preovulatory phase of the rat estrous cycle. (Endocrinology79: 907, 1966)