Long-term feed intake regulation in sheep is mediated by opioid receptors1

Abstract

These experiments were conducted to determine if 1) syndyphalin-33 (SD33), a mu-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 micromol/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 micromol/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 micromol of SD33/kg of BW, 0.1 microg 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.

TRIENNIAL GROWTH SYMPOSIUM: Neural regulation of feed intake: Modification by hormones, fasting, and disease1,2

“…which produced an increase in feed intake that was detected at 24 h and continued to at least 48 h after injection. Moreover, its effects were blocked by naloxone, indicating the feed intake response was mediated by opiate receptors (Obese et al, 2007). In a recent study in pigs, Kojima et al (2009) found a small increase in feed intake in pigs treated with SD33 just after weaning.…”

“…Enkephalin expression in the PVN and VMN, both areas involved in satiety, was reduced in thin as compared with fat ewes (Henry et al, 2000) but long-term undernutrition had no effect on prodynorphin mRNA in sheep (Iqbal et al, 2003). Injection of the opiate antagonist naloxone was found to inhibit feed intake in sheep, suggesting a stimulatory role for opiate receptors in regulating feed intake (Alavi et al, 1991;Obese et al, 2007), though naloxone was ineffective in alteration of feed intake in pigs (Baldwin and Parrot. 1985).…”

Effects of a dietary sweetener on growth performance and health of stressed beef calves and on diet digestibility and plasma and urinary metabolite concentrations of healthy calves1

“…Serum prolactin concentrations and area under the prolactin curve (Table 5) were not affected by treatment (P ≥ 0.20), and there was no treatment × time interaction (P = 0.41). Prolactin was employed as an indirect indicator of opioid peptide action because opioids have been widely implicated in feed intake regulation (Obese et al, 2007). Hart and Cowie (1978) reported that i.v.…”

Effects of Chronic Morphine Treatment on an Odor Conditioning Paradigm, Locomotor Activity and Sucrose Responsiveness in Honeybees (Apis mellifera)

“…Studies have found that opioids administration increases food intake in rats (Woods and Leibowitz, 1985) and sheep (Obese et al, 2007;Verbeek et al 2012), indicating a role of endogenous opioid peptides in feeding behavior. However, because of the bitter taste of morphine, we could not sure that bees would like to drink morphine when provided orally.…”