THE EFFECT OF PROGESTERONE ON PERSISTENT VAGINAL ESTRUS PRODUCED BY HYPOTHALAMICLESIONS IN THE RAT1

Abstract

Bilateral hypothalamic lesions ranging from the optic chaisma to the mammillary bodies were produced stereotaxically in 197 young adult female rats. Lesions in the posterior hypothalamus had no effect on the sexual cycles. Of the animals with anterior hypothalamic lesions, 33 entered persistent vaginal estrus, 7 had prolonged diestrus, and 7 had alternating periods of prolonged estrus and diestrus. Daily admn. of 0.5 mg. progesterone to persistent-estrous animals was followed by a resumption of fairly normal vaginal cycles and corpus luteum formation. Pseudopregnancy could be induced by cervical stimulation in the persistent-estrous animals during the periods that they had progesterone-induced vaginal cycles but not while they had continuous vaginal cornification. Progesterone, in the dosage administered, had no effect on hypothalamic animals with prolonged diestrus or on normal animals, as measured by the vaginal and uterine response. The mechanism of action of progesterone in inducing normal cyclic behavior in lesioned animals is unknown, but the phenomenon indicates that the changes in the reproductive cycle following hypothalamic lesions are of a secondary nature and that the primary cyclic mechanism is capable of being reactivated.