Maintenance by L-DOPA treatment of estrous cycles and LH response to estrogen in aging female rats

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Abstract
Nineteen, non-cycling female rats, 13–15 months of age, were fed 125 mg L-DOPA/15 g feed daily, and nineteen control rats of the same age were provided feed without L-DOPA. Sixteen of the L-DOPA fed rats each demonstrated 1–7 (average = 3) vaginal estrous cycles during the 75-day period of treatment, whereas no cycles were observed in the untreated controls. All animals were then ovariectomized and the post-castration rise in LH was monitored. Four weeks after ovariectomy, serum LH levels in the L-DOPA treated old female rats were significantly higher than in the non-treated old female rats. A single injection of 20μg of estradiol benzoate (EB) significantly lowered serum LH in the L-DOPA treated rats, but no effect was observed in the non-treated controls. A second injection of EB three days later produced a significantly greater LH surge in the old rats given L-DOPA than in the non-L-DOPA treated controls. These results indicate that prolonged L-DOPA administration can partially prevent the decline in function of the hypothalamo-pituitary-ovarian system in aging female rats.