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Regular Article |
a Animal Reproduction Laboratory, Texas A&M University Agricultural Research Station, Beeville, Texas 78102
b Department of Animal Science
c Center for Animal Biotechnology and Genomics, Texas A&M University, College Station, Texas 77843
d Department of Animal and Wildlife Sciences, Texas A&M University—Kingsville, Kingsville, Texas 78363
e Department of Animal Science, University of Missouri, Columbia, Missouri 65211
The present studies tested the hypotheses that short-term fasting would reduce leptin gene expression and circulating concentrations of leptin and insulin in mature, ovariectomized, estradiol-implanted cows and that intracerebroventricular infusions of recombinant ovine leptin (oleptin) would attenuate reductions in insulin concentration and stimulate LH secretion. Ovariectomized cows were assigned to either control (normal fed; n = 6) or fasted (60 h of fasting; n = 7) groups and infused with 200 µg recombinant oleptin three times at hourly intervals on Day 2 (n = 6 per group). Fasting decreased plasma concentrations of insulin (P < 0.01) and leptin (P < 0.04) but, as expected, did not reduce plasma concentrations of glucose or any LH secretion variable. Central infusion of leptin on Day 2 increased (P < 0.01) plasma concentrations of leptin in both control and fasted groups. Concomitantly, leptin treatment increased plasma insulin (P < 0.01) and LH (P < 0.03) concentrations in fasted but not in control cows. Increases in overall mean and baseline concentrations of LH after leptin treatment were the result of an augmentation of the size of LH pulses. The effects of fasting on leptin gene expression and the potential diurnal effects on circulating leptin were examined in a group of cows (n = 12) not treated with leptin. Fasting for 60 h reduced (P < 0.001) leptin gene expression by 30%, and no diurnal effects on circulating leptin were observed. These results indicate that although short-term fasting does not reduce the frequency or amplitude of LH pulses or the concentration of LH in mature cows, this nutritional perturbation clearly sensitizes both the hypothalamic-pituitary axis and endocrine pancreas to exogenous leptin, which in these experiments resulted in heightened secretion of both LH and insulin.
1 Supported by USDA-NRI 00-35203-9132 and Project H-6881 of the Texas Agricultural Experiment Station. A preliminary report of this work was presented at the 33rd Annual Meeting of the Society for the Study of Reproduction.
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; glw{at}fnbnet.net
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