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Gonadotropin-Releasing Hormone Overrides the Negative Effect of Reduced Dietary Energy on Gonadotropin Synthesis and Secretion in Ewes^*

J.P. KILE, B.M. ALEXANDER, G.E. MOSS, D.M. HALLFORD and T.M. NETT

Animal Reproduction & Biotechnology Lab (J.P.K., T.M.N.), Colorado State University Ft Collins, Colorado 80523
Department of Animal Science (B.M.A., G.E.M.), University of Wyoming Laramie, Wyoming 82071
Department of Animal and Range Sciences (D.M.H.), New Mexico State University Las Cruces, New Mexico 88003

Abstract

During prolonged periods of reduced dietary energy, there is a reduction in secretion of LH in females. To test the hypothesis that decreased secretion of LH is due to reduced secretion of GnRH, 18 ovariectomized ewes were fed either a low-energy diet (LOW, 60% of the National Research Council recommendations, n = 12) or a normal diet, (control, n = 6), for 127 days. Each ewe received basal levels (-5 pg/ml) of estradiol via sc Silastic implants. After 127 days, serum concentrations of FSH and LH were reduced (P < 0.05) by 63% and 77%, respectively in LOW ewes compared to control ewes. Pituitary concentrations of FSH and LH in LOW ewes also were reduced by 56% and 80%, respectively. Compared to levels in control ewes, concentrations of messenger RNAs for -, FSHβ-, and LHβ- subunits were reduced by 75%, 76%, and 91%, respectively. Pulsatile administration of GnRH (250 ng/2 h) for three weeks to LOW ewes restored each of the parameters to levels not different from those in controls. By the end of the study, serum concentrations of GH in all LOW animals had risen dramatically, but not in control ewes. Therefore, it appears that exogenous GnRH is capable of restoring synthesis and secretion of gonadotropins in ewes receiving low-energy diets. These results provide support for the hypothesis that reduced dietary energy results in decreased secretion of GnRH. (Endocrinology 128: 843–849, 1991)

Footnotes

^* This work was supported by a grant from the Colorado Agricultural Experiment Station.

Supported by NIH training Grant HD-07031.

Received June 6, 1990.

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