Effect of Intraportal and Continuous Intrajugular Administration of Insulin on Feeding in Sheep

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Abstract
The effect of intraportal and intrajugular administration of insulin on feed intake and on glucose and insulin of jugular blood was studied. Ad libitum intake of four wethers was measured and jugular blood was sampled at various times after intraportal administration of the treatments and meal initiation. The treatments injected in the first experiment were saline, 2 mU, 4 mU and 6mU insulin/kg body weight (BW), and in a second experiment were saline, 2 mU, 6 mU and 12 mU insulin/kg BW/minute infused over a 15-minute period. Feed intake was depressed only by 15-minute intraportal infusion of the 2 mU and 6 mU doses. Plasma insulin was elevated at 5 minutes after injection of 4 mU and 6 mU insulin/kg BW, and elevated at 5 and 15 minutes after 15-minute infusion of all three treatments; plasma glucose was not affected. Two additional experiments used four wethers in which jugular blood was sampled during a 24-hour intrajugular infusion of insulin. The combined treatments were saline, 0.02 mU, 0.2 mU, 2 mU and 6 mU insulin/kg BW/minute. The 6 mU dose stimulated feed intake, 2 mU increased plasma insulin and both 2 and 6 mU depressed plasma glucose. Thus, the site, timing and amount of exogeneous insulin administration may cause varying feed intake responses. The results are discussed with respect to a possible role of insulin in appetite control in sheep.