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Central role of the melanocortin-4 receptors in appetite regulation after endotoxin
JOURNAL OF ANIMAL SCIENCE (2008)
  • James L Sartin, Auburn University Main Campus
  • D L Marks, Oregon Health & Science University
  • Chris D McMahon
  • Joseph A Daniel, Berry College
  • P Levasseur, Oregon Health & Science University
  • C G Wagner, Auburn University Main Campus
  • Brian K Whitlock, University of Tennessee - Knoxville
  • Barbara P Steele, Auburn University Main Campus
Abstract
Melanocortin-4 receptors (MC4R) are key factors in the depression of appetite during disease. This study was designed to determine the role of agouti-related protein (AgRP) in the effect of endotoxin (lipopolysaccharide, LPS) on appetite. Sheep received an intracerebroventricular injection of either saline or AgRP (0.5 nmol/kg of BW) 1 h before intravenous injection of either saline or LPS (0.6 mu g/kg of BW) at time 0 and again at 4 h. Agouti-related protein prevented the reduction in feed intake due to LPS (P < 0.05). In a second experiment, AgRP gene expression was unaffected at 3 h and increased (P < 0.01) at 6 h after LPS. Immunohistochemical evidence indicated that there was an increase in the percentage of AgRP neurons with c-Fos immunoreactive nuclei 6 h after sheep were injected with LPS (P < 0.04) and a corresponding decrease in alpha-melanocyte-stimulating hormone neurons coexpressing c-Fos (P < 0.001). In situ hybridization provided evidence for an increase in AgRP gene expression and a decrease in proopiomelanocortin gene expression 6 h after LPS (P < 0.05). In a final experiment, physiological elevation of orexigenic agents by short-term fasting kept feed intake at the same level as controls, in spite of the presence of LPS, similar to the effects of AgRP in Exp. 1. The AgRP inhibition of the MC4R prevents appetite inhibition in response to LPS and well after LPS inhibition of feed intake, both AgRP and alpha-melanocyte-stimulating hormone may change in a pattern that favors appetite increases. These studies support the notion of the MC4R as a critical component of the mechanism for appetite suppression due to endotoxin.
Keywords
  • agouti-related protein,
  • food intake,
  • hypothalamus,
  • melanocortin-4 receptor,
  • alpha-melanocyte-stimulating hormone,
  • sheep
Publication Date
2008
Citation Information
James L Sartin, D L Marks, Chris D McMahon, Joseph A Daniel, et al.. "Central role of the melanocortin-4 receptors in appetite regulation after endotoxin" JOURNAL OF ANIMAL SCIENCE Vol. 86 Iss. 10 (2008)
Available at: http://works.bepress.com/brian_whitlock/9/