Effects of central administration of glucagon on feed intake and endocrine responses in sheep

This study was conducted to investigate effects of glucagon intracerebroventricularly administered on feed intake and endocrine changes in sheep. Four male sheep (48-55 kg BW) were used. The animals were acclimatized to be fed alfalfa hay cubes at 12.00 hour. Human glucagon (40 and 80 mu g/0.5 mL) was injected into the lateral ventricle at 12.00 hour. Blood samples were taken every 10 min from 30 min before to 180 min after the glucagon injection. Soon after the injection, the animals were given alfalfa hay cubes, and the amounts of the feed eaten within 2 h were measured. Feed intakes were significantly (P < 0.05) suppressed by 80 mu g of glucagon. Plasma glucose levels in control animals were gradually decreased after the feeding, whilst those in glucagon-treated animals were temporarily elevated just after the feeding and then kept higher than control levels. Plasma insulin was abruptly elevated after the feeding and was maintained at higher levels than before the feeding in all treatments. Plasma NEFA concentrations were decreased after the feeding in all treatments. A tendency of increase in plasma cortisol levels occurred in glucagon-injected animals. The present study provides the first evidence that glucagon directly acts on the brain, then inhibiting feeding behavior and inducing endocrine responses in ruminants.