Failure to Induce Ovulation in Constant Estrous Guinea Pigs. ∗

Ovulation may be induced in the rabbit, which normally ovulates only following copulation, by injecting a dilute solution of copper acetate either intravenously 1 or else into the third ventricle. 2 This reaction fails to occur after transection of the hypophysial stalk. 3 Acetylcholine, on the other hand, induces ovulation in the rat regardless of whether the stalk is intact or not. 4

Guinea pigs with large lesions in the anterior hypothalamus at the caudal border of the optic chiasma fail to ovulate postoperatively. 5 The vaginal membranes of these animals remain constantly open and the genitalia increase markedly in size. The ovaries resemble those of the pre-copulatory rabbit, i.e., ovarian follicles develop but ovulation does not occur spontaneously and corpora lutea are not formed. This disturbance of genital function appears to be due to the failure of the pituitary to release luteinizing hormone. When this hormone is administered artificially, the ovarian follicles rupture, corpora lutea are formed and the vaginal membrane closes. A single injection of luteinizing hormone is sufficient to cause this reaction. The vaginal membrane remains closed for an entire cycle (13-16 days) once lutein-ization is effected. 6