THE EFFECT OF ESTROGEN ON PLASMA LUTEINIZING HORMONE (LH) ACTIVITY IN THE RAT1

Abstract

Using the ovarian ascorbic acid assay for LH, detectable quantities of LH were found in plasma of ovariectomized donor rats. The LH activity of ovariectomized rat plasma was decreased by single subcutaneous injections of cstradiol benzoate (Eb). This effect was demonstrable within a day after injection of a large dose of Eb (50 μg); the minimal effective dose of Eb to cause a decrease in LH activity 3 days after injection was about 0.1 μg. A slight decrease in LH activity was demonstrable within an hour of intravenous injection of a large dose of estradiol (E) or Eb. Decreased LH activity was found in the absence of proestrous or estrous smears but was always found if the smear was in proestrous or estrous stage. It was concluded that E exerts a negative feed-back on the LH controlling area(s).