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BOR - Papers in Press, published online ahead of print May 5, 2004.
Biol Reprod 2004, 10.1095/biolreprod.104.028548
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BIOLOGY OF REPRODUCTION 71, 804–812 (2004)
DOI: 10.1095/biolreprod.104.028548
© 2004 by the Society for the Study of Reproduction, Inc.

Neuroendocrinology

Regulatory Roles of Leptin at the Hypothalamic-Hypophyseal Axis Before and after Sexual Maturation in Cattle1

D.A. Zieba3,4,5, M. Amstalden3,4,5, S. Morton3,4,5, M.N. Maciel3,4,5, D.H. Keisler6, and G.L. Williams2,3,4,5

Animal Reproduction Laboratory,3 Texas A&M University Agricultural Research Station, Beeville, Texas 78102 Department of Animal Science4 Center for Animal Biotechnology and Genomics,5 Texas A&M University, College Station, Texas 77843 Department of Animal Science,6 University of Missouri, Columbia, Missouri 65211

Studies assessed, either directly or indirectly, the role of GnRH in leptin-mediated stimulation of LH release in cattle before and after sexual maturation. In experiment 1, the objectives were to determine whether leptin could acutely accelerate the frequency of LH pulses, and putatively GnRH pulses, in prepubertal heifers at different stages of development. In experiment 2, we determined directly whether acute, leptin-mediated increases in LH secretion in the fasted, mature female are accompanied by an increase in GnRH secretion. Ten-month-old prepubertal heifers (experiment 1) fed normal- (n = 5) and restricted-growth (n = 5) diets received three injections of saline or recombinant ovine leptin (oleptin; 0.2 µg/kg body weight, i.v.) at hourly intervals during 5-h experiments conducted every 5 wk until all normal-growth heifers were pubertal. Leptin increased mean concentrations of circulating LH regardless of diet, but pulse characteristics were not altered at any age. In experiment 2, ovariectomized, estradiol-implanted cows (n = 5) were fasted twice for 72 h and treated with either saline or oleptin i.v. (as in experiment 1) on Day 3 of each fast. Leptin increased plasma concentrations of LH and third ventricle cerebrospinal fluid concentrations of GnRH, and increased the amplitude of LH and the size of GnRH pulses, respectively, on Day 3 of fasting compared to saline. Overall, results indicate that leptin is unable to accelerate the pulse generator in heifers at any developmental stage. However, leptin-mediated augmentation of LH concentrations and pulse amplitude in the nutritionally stressed, mature female are associated with modifications in GnRH secretory dynamics.

1 Supported by USDA-NRI 00-35203-9132.

2 Correspondence: G.L. Williams, Animal Reproduction Laboratory, Texas A&M University Agricultural Research Station, 3507 Hwy 59 E, Beeville, TX 78102-9410. FAX: 361 358 4930; glwilliams{at}tamu.edu






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Copyright © 2004 by the Society for the Study of Reproduction.