title: Response of plasma leptin concentration to jugular infusion of glucose or lipid is dependent on the stage of lactation of Holstein cows.
abstract: In this study we investigated the hormonal and metabolite responses to isoenergetic jugular infusions of glucose or lipid in early- and late-lactation Holstein cows. Six Holstein cows were used in a replicated Latin square design with jugular infusions of either 1) control (CON; saline), 2) glucose (GLU; 50% dextrose) or 3) lipid (LIP; 20% Intralipid). Treatments did not affect dry matter intake, with the exception of a hypophagic effect of LIP in late lactation. The GLU-induced hyperglycemia and hyperinsulinemia were greater in late-lactation than in early-lactation cows. The GLU treatment did not affect plasma leptin and insulin-like growth factor-1 (IGF-1) concentrations in early-lactation cows, but it increased them in late-lactation cows. The LIP treatment did not affect plasma leptin, insulin and IGF-1 concentrations in early-lactation cows, despite a marked LIP-induced increase in plasma nonesterified fatty acid and beta-hydroxybutyrate concentrations and a reduction in growth hormone (GH) concentration. Compared with the delayed leptin response to GLU, the stimulatory effect of LIP on leptin secretion in late-lactation cows was relatively rapid and occurred in the absence of any significant changes in plasma insulin, IGF-1 or GH. We propose that insulin-mediated glucose metabolism may be involved in the stimulatory effects of glucose on leptin secretion in late-lactation animals but that the stimulatory effects of lipid are independent of insulin or IGF-1. In early-lactation animals a strong inhibitory effect of GH on leptin expression and release, in addition to low adipose reserves and/or energy balance, might override any short-term stimulatory effect of glucose or lipid on leptin secretion.
authors.affiliation: Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, Alberta, Canada T6G 2P5.
authors.forename: Prasanth K
authors.initials: PK
authors.lastname: Chelikani
authors.forename: Duane H
authors.initials: DH
authors.lastname: Keisler
authors.forename: John J
authors.initials: JJ
authors.lastname: Kennelly
mesh_terms: D000818:Animals; D002417:Cattle / Q000097:blood / Q000502:physiology*; D005217:Fat Emulsions, Intravenous / Q000008:administration & dosage*; D005260:Female; D005947:Glucose / Q000008:administration & dosage*; D006728:Hormones / Q000097:blood; D007262:Infusions, Intravenous; D007601:Jugular Veins; D007774:Lactation / Q000502:physiology*; D020738:Leptin / Q000097:blood*
chemical_list: D005217:Fat Emulsions, Intravenous; D006728:Hormones; D020738:Leptin; D005947:Glucose