Luteinizing Hormone in Persistent Vaginal Œstrus

Abstract

THE placement of experimental lesions in the anterior part of the hypothalamus may be followed by persistent vaginal œstrus in the guinea pig and rat. Such animals possess relatively small ovaries which have no fresh corpora lutea. Various attempts have been made to explain these effects in terms of an altered output of gonadotrophins by the pituitary gland. The original view that the secretion of luteinizing hormone was blocked¹ was supported by Van Dyke et al.², who found that in animals with persistent œstrus induced by lesions, the ovarian interstitial tissue showed a high lipid content indicative of deficiency in luteinizing hormone. Recently, Taleisnik and McCann³ reported a pituitary luteinizing hormone content in animals with persistent œstrus which was lower than in intact animals. However, after gonadectomy the amount of luteinizing hormone of persistently œstrous rats showed an increase, but the level of hormone in plasma remained low, indicating that the pituitary release of the hormone is blocked. On the other hand, Hillarp⁴ concluded, also on the basis of the condition of the ovarian interstitial tissue, that during persistent œstrus luteinizing hormone was still being secreted in considerable amounts. In other work, the possibility was stressed that in persistent œstrus induced by lesions, secretion of follicle stimulating hormone may be enhanced, because in animals which had been operated during the first two weeks after birth, puberty occurred at an earlier age than in control animals. After puberty, a number of these animals showed persistent œstrus⁵. A third possibility has been advanced by D'Angelo and Kravatz⁶, who assumed that in persistently œstrous rats secretion of follicle-stimulating hormone may be decreased. This assumption was based on their finding that the serum of unilaterally gonadectomized rats with persistent œstrus contained less follicle-stimulating hormone than that of cycling animals after removal of one ovary.