Ovulation induction with LH-RH in rats rendered acyclic by hypophysial grafts

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Abstract
As a model for the study of the correlation between control of prolactin and gonadotropin secretion, the intact female rat bearing a 2nd pituitary beneath the kidney capsule was adopted, and the ability of exogenous LH-RH [luteinizing hormone-releasing hormone] to induce ovulation in such animals was investigated. The model used confirms the observation of Qulligan and Rothchild (1960) that a foreign hypophysis implanted into an intact female rat can exert an influence on the animal''s own hormonal balance, resulting in a cessation of cyclic hormone changes and an elevation of serum prolactin concentrations, i.e., a state of pseudopregnancy. This condition was manifested by constant vaginal diestrus and anatomical changes in mammary glands, ovaries, uteri and vaginae observed in histological studies. Ovulatio induction in such animals with LH-RH was surprising, because a single LH-RH injection resulted in normal ovulatory plasma LH [luteinzing hormone] elevations but did not cause ovulation. The resistance of the histologically mature Graafian follicles to these LH elevations strongly suggests that an unidentified inhibitory factor is involved; the requirement of 3 successive LH-RH applications for ovulation would then be best explained by assuming the need for a priming effect at the hypophysis and the ovary before an ovulatory response becomes possible. The simple model described is ideally suited to studies for clarifying the inadequately understood relationships between prolactin and the gonadotropins.