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Biology of Reproduction 59, 960-968 (1998)
©Copyright 1998 Society for the Study of Reproduction, Inc.

Pulsatile Luteinizing Hormone Secretion in the Ovariectomized, Thyroidectomized Red Deer Hind Following Treatment with Dopaminergic and Opioidergic Agonists and Antagonists1

Greg M. Anderson3,a, , and Graham K. Barrell2,a

a Animal and Food Sciences Division, Lincoln University, Canterbury, New Zealand

Two experiments were conducted to determine whether dopaminergic or opioidergic pathways are modulated by thyroid gland secretions for seasonal suppression of LH secretion in red deer hinds. Ovariectomized (n = 5) or ovariectomized and thyroidectomized (n = 4) hinds, treated with estradiol implants, received the dopamine agonist bromocriptine or the antagonist sulpiride during pulse bleeds in July (breeding season) and October (nonbreeding season). Comparison of July and October mean plasma LH concentration (3.5 ± 1.3, 0.7 ± 0.1 ng/ml, respectively), pulse frequency (1.9 ± 0.4, 0.7 ± 0.2 pulses/4 h), and pulse amplitude (1.3 ± 0.5, 0.7 ± 0.02 ng/ml) showed lower (p < 0.05) levels in October, and these levels were not significantly affected by thyroidectomy or drug treatment. In the absence of estradiol implants, the hinds received bromocriptine or morphine during the breeding season (July) and their antagonists, sulpiride or naloxone, respectively, in the nonbreeding season (November). In euthyroid hinds there was a seasonal decrease (p < 0.05) in mean plasma LH concentration, pulse frequency, and pulse amplitude, which did not occur in thyroidectomized hinds. There were no effects of drug treatment on LH concentration except for a small increase following sulpiride in November. Plasma prolactin concentration was significantly increased by antagonists and decreased by agonists on most occasions. We conclude that in red deer hinds, seasonal regulation of LH secretion does not involve dopamine or endogenous opioids and the thyroid gland is required specifically for LH suppression in the absence of estradiol.

1 Financial assistance was provided by the Lottery Science Research Committee of the New Zealand Lottery Grants Board and by the Canterbury Branch of the New Zealand Deer Farmers Association.

2 Correspondence: Graham K. Barrell, Animal and Food Sciences Division, P.O. Box 84, Lincoln University, Canterbury, New Zealand. FAX: 64 3 3253851; barrell{at}whio.lincoln.ac.nz

3 Current address: Department of Physiology, West Virginia University, Morgantown, WV 26506–9229.






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Copyright © 1998 by the Society for the Study of Reproduction.