Effect of Reserpine on Plasma LH Levels in Ovariectomized and Cycling Proestrus Rats

Summary

The present experiments were carried out to determine the effects of drugs which are known to alter the stores of monoamines in the hypothalamus upon the concentration of LH in the blood of ovariectomized and normal rats. LH was estimated by the ovarian ascorbic acid depletion bioassay. In agreement with earlier data, blockade of ovulation occurred when reserpine (2 mg/kg) was administered prior to the assumed “critical” period of LH release and the effect could be overcome by prior treatment with a monoamine oxidase inhibitor, pargyline (25 mg/kg). Reserpine injection for 3 days (0.5 mg/kg) was shown to be effective in lowering the elevated plasma LH levels in ovariectomized rats. A significant level of LH was present in the blood during the afternoon of proestrus in control rats; whereas the levels were depressed after a single injection of reserpine (2 mg/kg) on the morning of proestrus. The blockade of the proestrous rise in plasma LH by injection of reserpine was prevented by prior treatment with pargyline (25 mg/kg). These results provide direct support for the hypothesis that LH secretion is regulated by hypothalamic monoaminergic mechanisms.