Regulation of Luteinizing Hormone (LH) in the Fetal and Neonatal Lamb: Effect of Castration During the Early Postnatal Period on Levels of LH in Sera and Pituitaries of Neonatal Lambs1

Abstract

To determine if the gonads of the immature sheep influence the secretion of luteinizing hormone (LH) during the first two weeks after birth, concentrations of LH in the peripheral blood of intact and castrated lambs of both sexes were compared. Pituitary weights, pituitary LH concentrations, and uterine weights were also compared. Neither an effect of castration nor sex was observed on the weight or LH concentration of the pituitary. The weight of the uterus was not influenced by castration. Mean levels of serum LH remained low (< 0.5 ng/ml) in intact males during the age period studied. Levels of circulating LH in the castrated males were elevated significantly 8 days after orchidectomy and continued to increase in an apparently erratic pattern during the final half of the experimental period. In both intact and ovariectomized females, concentrations of LH in the blood followed a trend similar to that of castrated males. The data suggest that: (a) negative feedback of gonadal steroid hormones on the hypothalamo-hypophyseal system becomes established earlier in the male in the female; (b) the neonatal ovary may not be producing a sufficient amount of the proper steroid to inhibit release of LH or to influence the growth of the uterus; and (c) residual effects of the recent intrauterine environment may influence the early postnatal secretion of LH. Comparison of these data with those found in the literature indicate that the failure of early castration to increase synthesis or storage of pituitary LH may be age or species dependent.