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Estrogen and L-Dihydroxyphenylalanine Induced Changes in Hypothalamic Biogenic Amine Levels and Serum LH in the Ewe^{1, 2,}

Oregon State University^,4, Corvallis 97331

Abstract

Experiments were conducted to determine the ability of exogenous L-dihydroxyphenylalanine (L-dopa) and 17ß-estradiol to alter the concentrations of hypothalarnic biogenic amines and affect the release of luteinizing hormone (LH) in the ewe. A single iv injection of L-dopa (7 mg/kg) into ewes on day 3 of the estrous cycle failed to elicit an LH release during the 32-hr sampling period in three of four animals. In one ewe, however, elevated serum LH concentrations of 19.6 and 91.3 ng/ml were detected at 24 and 32 hr post-injection of L-dopa, respectively. A single im injection of 750 µg of 17ß-estradiol into ewes at the same stage of the estrous cycle caused an increase in serum LH concentration in each ewe (range, 20 to 30 ng/ml) within 16 hr following treatment. A similar injection of estradiol into ewes 8 hr prior to necropsy on day 3 of the cycle was without effect on the concentrations of biogenic amines in the stalk median eminence (SME) or hypothalamus proper (HP). In both treated and control ewes, however, norepinephrine (NE) concentrations were higher (P < .01) in the HP than in the SME. Conversely, dopamine and serotonin concentrations were found to be higher (P < .01) in the SME than in the HP. Treatment of ovariectomized ewes with 750 µg of estradiol 3 hr prior to necropsy elevated NE concentrations in the SME (P .07) but failed to alter NE concentrations in the HP. Although not significant statistically, serotonin concentrations in both the SME and HP tended to increase after treatment of these ewes with estradiol. One hour after iv injection of ovariectomized ewes with L-dopa (12 mg/kg) biogenic amine concentrations in the SME and HP qualitatively resembled those detected in ewes following injection of estradiol.

¹ Technical Paper No. 3623, Oregon Agricultural Experiment Station.

² This investigation was supported by a special grant (No. 016-15-03) from the Cooperative State Research Service, U.S.D.A.

³ Appreciation is expressed to the Endocrinology Study Section, National Institutes of Health for the gift of NIH-LH-S17; Dr. G. D. Niswender for the anti-ovine LH serum and Dr. L.E. Reichert for the highly purified ovine LH (LER-1056-C2) which were used for LH radioimmunoassay.

⁴ Department of Animal Science.