Abstract
There is now considerable evidence that extracts of the median eminence region of the hypothalamus contain a substance which stimulates the release of ovulation hormone (LH) (1,2,3,4). We have recently reported partial purification of this substance (LRF, for LH-releasing factor) using the ovarian ascorbic acid depletion method as a test of endogenous release of LH(5). To validate any possible physiological significance of these observations we had to demonstrate that this material (LRF) would stimulate secretion of LH in animals in which the cyclic release of LH was blocked by a suitable hypothalamic lesion, the most specific criteria for LH-activity being used, i.e., ovulation with direct observation of tubal ova and subsequent formation of corpora lutea.
Materials and methods. Experiment I. Forty-two female rats, Wistar origin (Du-terme Farms, Condé s/Huisne, France) B. W. 170–200 g were utilized here. In each of them a hypothalamic lesion was produced by a high frequency coagulation between the tip of 2 electrodes (1.0 mm apart) descended simultaneously on each side of the sagittal sinus. The stereotaxic coordinates (Krieg-Johnson instrument, de Groot's coordinates) were: A = 6.4 mm, H = −2 mm. Vaginal smears were begun 2 months following placement of the lesion; they were read daily for 4 weeks. Of this series, 26 animals were considered to be in “persistent vaginal estrus” when there was predominance of epithelial or cornified cells in at least 90% of the daily vaginal smears. With randomization tables, they were divided into 5 groups; in the first one, 4 animals were sacrificed with no further treatment; the anterior lobes of the pituitary glands were extracted as a pool in 4.0 ml of ice cold saline, with a few grains of sand and a ground glass rod.
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