Endogenous Gonadotropic Activity in Mare Serum Subsequent to Chronic Treatment with Gonadotropin

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Abstract
Over 100 samples of sera from 2 mares chronically treated with HCG alone or combined with FSH as an antigen were tested for gonadotropic activity in normal immature female rats. The sera were also tested in normal immature males and in hypophysectomized male and female rats. An FSH-like response was obtained in the normal immature female rat with the sera of the mare treated with HCG alone for about a 6-month period after cessation of treatment with antigen. In the mare receiving the sequential treatment with HCG followed by FSH, a gonadotropic response was obtained with the sera for 7 weeks following withdrawal of treatment with antigens. Following a second series of treatments, sufficient anti-FSH, as well as anti-HCG, was present to mask any gonadotropic activity which the serum possessed for a 5-week period; following this the serum showed gonadotropic activity for 17 weeks. Finally, following a third series of treatment with FSH alone, no gonadotropic activity was observed for 24 weeks after the initial injection. Sera producing an ovarian and uterine response in normal immature female rats had no detectable effect on the ovaries of hypophysectomized female rats or on the testes of normal immature male rats. The testes weights of hypophysectomized male rats, on the other hand, were increased. In only one test out of 5 were the diameters of the seminiferous tubules significantly greater than in control animals. The relationship of anti-, pro- and gonadotropic activities of the antisera are discussed. All serum samples were tested for antigonadotropic and progonadotropic activity as well as for gonadotropic activity. The injection of anti-HCG serum with FSH caused an increase in ovarian weight up to 3 times that obtained by FSH alone. Many large follicles and corpora were present, as compared to the mild follicular growth obtained with FSH. In this respect the response to the antiserum is similar to that obtained by adding ICSH to FSH. Gonadotropic activity appears during and following high anti-HCG titers. In some instances pro- and gonadotropic activities parallel each other; in others they do not. The results are discussed in relation to the roles which FSH and ICSH play in gonadal development. Based on our current studies and those of other workers, we postulate that follicular growth, ovulation, estrogen secretion and corpus luteum formation all require the combined action of FSH and ICSH. (Endocrinology74: 52, 1964)