Role of Estrogen in the Cerebral Control of Puberty in Female Rats

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Abstract
The role of estrogen feedback on the hypothalamus in the control of the onset of puberty was studied in female Long-Evans rats. Twenty-six or 30-gauge tubes containing crystalline estradiol benzoate (EB) at their tips were implanted chronically (left in situ) or acutely (removed after 48 hr) in the brains of immature (26-day) or adult females. In each experiment cholesterol implants were used as controls. All chronic EB implants in the median eminence region severely inhibited uterine and ovarian development in the immature rats, but 30-gauge implants in adults produced a significant reduction only of uterine weight. Implants elsewhere did not affect ovaries or uteri at any age. Chronic EB implantation at 26 days (26- and 30- gauge implants) advanced vaginal opening by one week and disrupted vaginal cycling regardlessregardless of location (hypothalamus, midbrain, cortex), suggesting systemic release of the steroid. Acute EB implantation advanced vaginal opening only when implants were in the anterior hypothalamic-preoptic region (AH-PO), and this case ovaries, uteri and cycles appeared unchanged, indicating true precocious puberty. Acute implants in the median eminence region had no apparent effect. It is concluded that brief exposure to estradiol activates a positive feedback mechanism in the AH-PO, with resulting precocious puberty. Longer exposure of the median eminence produces negative feedback inhibition of gonadotropin secretion. The prepuberal median eminence seems more sensitive to this effect of estrogen than that of the adult female. (Endocrinology82: 100, 1968)