Positive and Negative Feedback Control by Estrogen of Luteinizing Hormone Secretion in the Rhesus Monkey12

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Abstract
Silastic capsules containing 17β–estradiol were implanted subcutaneously into rhesus monkeys ovariectomized 3–18 months earlier. These capsules released the steroid at a rate which resulted in plasma estrogen concentrations (70 pg/ml) approximating those observed during the early follicular phase of the normal menstrual cycle. These estrogen levels were maintained for as long as the implants were kept in place (1 yr and 9 months). Following the implantation of estradiol, the elevated plasma LH concentrations characteristic of untreated ovariectomized monkeys declined to the low levels associated with the early follicular phase of the cycle and remained there for the duration of the study. The administration of a single subcutaneous injection of estradiol benzoate to these chronically suppressed ovariectomized animals elicited a discharge of LH resembling the spontaneous, preovulatory LH surge. These findings support the conclusion that the positive feedback action of estradiol, which initiates the LH surge, is superimposed upon, and independent of, the negative feedback control of LH secretion. The results further suggest that the patterns of LH secretion throughout the normal menstrual cycle can be accounted for, primarily, by alterations in ovarian estrogen secretion. (Endocrinology92: 799, 1973)

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