Time of Release of Pituitary Gonadotropin Induced by Electrical Stimulation of the Rabbit Brain

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Abstract
The release of progestin into the ovarian vein has been employed as an indicator of the release of pituitary ovulating hormone in the rabbit. The principal progestin found in the ovarian venous effluent of this reflexly ovulating species is 20α-hydroxypregn- 4-en-3-one, which is readily measured by physicochemical methods. Following coitus or intravenous administration of luteinizing hormone, there is an immediate preovulatory synthesis and release of this progestational steroid. In sexually mature rabbits, bipolar concentric electrodes were implanted chronically in various parts of the hypothalamus and in the temporal lobes, and these sites were excited electrically under chloralosane anesthesia while blood was being collected from the ovarian vein. Electrical excitation of the posterior median eminence and basal tuberal region of the hypothalamus or the medial amygdala at parameters which subsequently induced ovulation usually produced an immediate increase in ovarian progestin output which continued to rise for the 30-min period after stimulation, whereas stimulation of closely adjacent regions of the hypothalamus and temporal lobes produced neither a rise in progestin nor ovulation. These results, based on ovarian progestin output, indicate that the pituitary can respond to electrical stimulation of the brain by a rapid release of ovulating hormone similar in time sequence to that which follows the mating stimulus. (Endocrinology74: 108, 1964)

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