Long-term feed intake regulation in sheep is mediated by opioid receptors

• Published in: Journal of animal science Vol. 85; no. 1; pp. 111 - 117
• Main Authors: Obese, F.Y, Whitlock, B.K, Steele, B.P, Buonomo, F.C, Sartin, J.L
• Format: Journal Article
• Language: English
• Published: Savoy, IL American Society of Animal Science 2007; Am Soc Animal Sci
• Subjects: Animal productions; Animals; Bacteria - metabolism; Biological and medical sciences; dosage; dose response; Dose-Response Relationship, Drug; feed concentrates; feed intake; feed intake regulation; Feeding Behavior - drug effects; Feeding Behavior - physiology; Fundamental and applied biological sciences. Psychology; ligands; lipopolysaccharides; Lipopolysaccharides - toxicity; Male; males; Naloxone - pharmacology; Narcotic Antagonists - pharmacology; Oligopeptides - pharmacology; opioid peptides; receptors; Receptors, Opioid - metabolism; sheep; Sheep - physiology; syndyphalin-33; temporal variation; Terrestrial animal productions; Vertebrates; Appetite; Farming animal; Animal feeding; feed intake; Endotoxin; Long term; opioid receptor; Toxin; Vertebrata; Meat animals; Mammalia; syndyphalin-33; Sheep; Artiodactyla; Ungulata
• ISSN: 0021-8812; 1525-3163
• DOI: 10.2527/jas.2006-404

These experiments were conducted to determine if 1) syndyphalin-33 (SD33), a μ-opioid receptor ligand, affects feed intake; 2) SD33 effects on feed intake are mediated by actions on opioid receptors; and 3) its activity can counteract the reduction in feed intake associated with administration of bacterial endotoxin. In Exp. 1, 5 mixed-breed, castrate male sheep were housed indoors in individual pens. Animals had ad libitum access to water and concentrate feed. Saline (SAL; 0.9% NaCl) or SD33 (0.05 or 0.1 μmol/kg of BW) was injected i.v., and feed intake was determined at 2, 4, 6, 8, 24, and 48 h after the i.v. injections. Both doses of SD33 increased (at least P < 0.01) feed intake at 48 h relative to saline. In Exp. 2, SAL + SAL, SAL + SD33 (0.1 μmol/kg of BW), naloxone (NAL; 1 mg/kg of BW) + SAL, and NAL + SD33 were injected i.v. Food intake was determined as in Exp. 1. The SAL + SD33 treatment increased (P = 0.022) feed intake at 48 h relative to SAL + SAL. The NAL + SAL treatment reduced (at least P < 0.01) feed intake at 4, 6, 8, 24, and 48 h, whereas the combination of NAL and SD33 did not reduce feed intake at 24 (P = 0.969) or 48 h (P = 0.076) relative to the saline-treated sheep. In Exp. 3, sheep received 1 of 4 treatments: SAL + SAL, SAL + 0.1 μmol of SD33/kg of BW, 0.1 μg of lipopolysaccharide (LPS)/kg of BW + SAL, or LPS + SD33, and feed intake was monitored as in Exp. 1. Lipopolysaccharide suppressed cumulative feed intake for 48 h (P < 0.01) relative to saline control, but SD33 failed to reverse the reduction in feed intake during this period. These data indicate that SD33 increases feed intake in sheep after i.v. injection, and its effects are mediated via opioid receptors. However, the LPS-induced suppression in feed intake cannot be overcome by the opioid receptor ligand, SD33.