Inhibition of Gonadotropin Secretion During Lactation in the Rat: Relative Contribution of Suckling and Ovarian Steroids1

Abstract

The relative effects of the suckling stimulus and ovarian steroids on gonadotropin inhibition during lactation were studied in intact and ovariectomized lactating rats. On Day 2 postpartum, litter sizes were adjusted to 0 or 8 pups and ovariectomy was performed. Serum LH concentrations in the intact lactators were barely detectable and approximately five-fold lower than basal cycling levels reported previously by this laboratory. Serum and pituitary LH concentrations gradually increased in ovariectomized lactators but did not differ markedly from intact lactators until Days 15 to 20 postpartum. At all times studied, the postcastration rise in serum and pituitary LH was clearly inhibited in ovariectomized lactators when compared to nonlactating, ovariectomized females.