A NEUROGENIC TIMING FACTOR IN CONTROL OF THE OVULATORY DISCHARGE OF LUTEINIZING HORMONE IN THE CYCLIC RAT1

Abstract

Dibenamine or atropine will block the mechanism which leads to release of LH from the adenohypophysis after estrogen injn. Since these drugs do not interfere with the glandular discharge of the hormone nor with its action on the ovary, the conclusion was reached that estrogen effects LH release at least partially by way of the nervous system, presumably the hypothalamus. The existance in the cyclic rat of a similar mechanism and the chronologic relationship of this to the cycle are demonstrated in the present report, which concerns the results of injns. of Dibenamine or of atropine at various hrs. of the day of proestrus. Excepting preliminary expts., the animals used were 68 4-day cyclic rats belonging to a strain in which ovulation normally occurs between 1 and 2:30 A.M. in the early morning after proestrus. When Dibenamine was injd. during proestrus at 2 P.M. or earlier, ovulation was prevented or significantly retarded in most cases. Injection of atropine at these hours uniformly prevented preovulatory swelling or ovulation. Associated with these blocking effects of either drug was the failure of both the ovarian interstitial tissue to undergo the usual cholesterol depletion and of the corpora lutea of the preceding cycle to store cholesterol. The uteri usually remained distended the day after injn. In most cases the vaginal smear sequence was retarded significantly. When either drug was injd, at 4 P.M. during proestrus, ovulation proceeded without detectable interference apart from retardation in a few rats treated with Dibenamine. In the majority of cases the only suggestion of an effect upon LH release was an apparent delay of luteal cholesterol storage. It is concluded that in this strain of rats, under our colony conditions, neurochumoral stimulation of the adenohypophysis occurs during proestrus between 2 and 4 P.M., 10-12 hrs. before ovulation. The demonstration that this chronologically limited neurohumoral stimulus is essential to adequate release of LH clearly offers a means by which various features of the polyestrous cycle may be synchronized with environmental rhythms.