Pituitary Concentration of Luteinizing Hormone in Three Types of “Constant Estrous” Rats

Abstract

To compare the mechanisms involved in the production of persistent vaginal cornification, pituitary concentrations of LH were measured in rats made "persistent estrus" with hypothalamic lesions, testosterone injection at 5 days of age, or exposure to constant light. Pituitary LH was measured in pooled saline extracts, using the ovarian ascorbic acid depletion method, in all groups following 35-40 days of vaginal cornification and also after 10-13 days of cornification in constant light- and testosterone-treated rats. Pituitaries collected from normal animals during each of the days of the estrous cycle were used for reference; since testosterone-treated rats were younger than the other experimental groups at autopsy, glands from normal estrous litter mates were used for comparison. In normals, LH concentration was 2.45 [mu]g/mg at proestrus and 1.19 [mu]g/mg at estrus. Progressive increases in LH were found during the 3 days of diestrus. While glands from rats with constant light- and testosterone-induced "persistent estrus" had LH levels less than those of appropriate controls, pituitaries of lesioned animals had a concentration which was greater than that of cyclic rats on the day of estrus. This concentration was significantly higher than that seen in the constant light- or testosterone-treated rats which had been in "persistent estrus" for the same length of time. The results suggest that, despite similarities of ovarian and vaginal changes, constant light and testosterone produce effects on neural LH-regulating mechanisms which differ from those caused by lesions.