STIMULATING AND INHIBITING EFFECTS OF PROGESTERONE ON THE RELEASE OF LUTEINIZING HORMONE

Abstract

ABSTRACT Plasma LH was determined in ovariectomized-oestrogen treated rats by the ovarian ascorbic acid method. The elevated plasma LH of the spayed animals was found to be depressed on the third day after a single injection of 20 μg oestradiol benzoate. Progesterone (2 mg) injected on the third day after oestrogen induced an increase in plasma LH a few hours later. This effect of progesterone was evident only when blood was drawn in the afternoon, but not when blood was drawn in the morning. In hypophysectomized animals progesterone failed to change plasma LH activity. On the afternoon of the fourth day after the injection of oestrogen, the plasma LH returned to the elevated preinjection levels. However, when progesterone was administered on the 3rd day these elevated levels were markedly depressed. It is concluded that progesterone has a biphasic effect, first stimulating and then inhibiting, on the release of LH.