Effects of a single day of feed restriction on changes in serum leptin, gonadotropins, prolactin, and metabolites in aged and young mares.
In a variety of species, short-term feed restriction leads to rapid changes in the reproductive axis and reduces serum levels of leptin. Two experiments were performed to test the hypothesis that a single day of feed restriction in aged and young mares would cause a suppression of the gonadotropins and serum leptin concentrations. The estrous cycles of 12 aged (>eight years; Exp. 1) and eight young (<five years; Exp. 2) mares were synchronized and the mares were conditioned to twice-daily meal feeding. On the seventh day after synchronization, restricted mares (n = 6 for Exp. 1; n = 4 for Exp. 2) were not fed for 24 hr; all mares were fed the second day. In Exp. 1, serum leptin concentrations significantly decreased in restricted mares, but not in controls. In Exp. 2, serum leptin concentrations declined in restricted mares and no decline was seen in the controls. Serum glucose concentrations did not change in response to feed restriction or refeeding, but in both experiments feed restriction caused an increase in free fatty acids. For both experiments, prolactin, FSH, and LH serum concentrations were not significantly altered by feed restriction. The observed absence of suppression may reflect the maintenance of sufficient levels of metabolizable fuels, rather than a failure of leptin to signal nutritional status to the reproductive axis of the mare.
McManus
C J
CJ
Department of Veterinary Science; Maxwell Gluck Equine Research Center, University of Kentucky, Lexington, KY 40546-0099, USA. cjmcma00@pop.uk.edu
Fitzgerald
B P
BP
D000375:Aging / Q000502:physiology*; D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D004973:Estrus Synchronization; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D005502:Food; D005508:Food Deprivation / Q000502:physiology*; D006065:Gonadotropins, Pituitary / Q000097:blood*; D006736:Horses / Q000097:blood*; D007700:Kinetics; D020738:Leptin / Q000032:analysis*; D007986:Luteinizing Hormone / Q000097:blood; D011388:Prolactin / Q000097:blood*
D001786:Blood Glucose; D006065:Gonadotropins, Pituitary; D020738:Leptin; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone