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Abstract
The effects of intravenous somatostatin-28 (S28) infusion on glucose-stimulated and glucagon-like peptide-1(7–36)amide (GLP-1)-augmented insulin secretion were studied in sheep. S28 was infused via a jugular catheter for 15 min at a rate of 1·1 pmol/kg/min either alone or together with GLP-1 and/or glucose. S28 infusion did not significantly lower circulating basal insulin concentrations in fed sheep. Glucose-stimulated insulin secretion was significantly inhibited by S28 infusion, serum concentrations decreasing from about 200 to 150 pmol/l. GLP-1 significantly augmented glucose-stimulated insulin secretion, serum concentrations increasing from about 230 to 280 pmol/l. S28 completely counteracted this effect of GLP-1. S28 infusion also significantly decreased the circulating concentrations of glucose-dependent insulinotrophic polypeptide (GIP) and GLP-1 in fed sheep (from about 110 to 45 pmol/l for GIP and from about 25 to 15 pmol/l for GLP-1). The physiological implications of these observations are discussed with particular reference to the ruminant. It is concluded that S28 may have an important endocrine role in the control of insulin secretion and regulation of nutrient partitioning.
Journal of Endocrinology (1996) 151, 107–112
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ABSTRACT
The effects of i.v. glucagon-like peptide-1-(7–36)amide (GLP-1; 10 μg) on starved sheep given an i.v. glucose load (5 g) were studied. Plasma insulin concentrations rose significantly more after glucose administration in fed than in starved sheep. Giving GLP-1 to starved sheep increased the insulin response to the glucose load. The rise in plasma insulin concentrations in starved sheep given GLP-1 was similar to that observed in fed sheep. Plasma glucose concentrations returned to normal values more quickly in the starved sheep given GLP-1 than in starved sheep not given gut hormone. Plasma concentrations of free fatty acid, urea and α-amino nitrogen decreased more quickly following glucose administration in starved sheep given GLP-1 than in those not given GLP-1. The data suggest a role for GLP-1 in regulating plasma insulin concentrations and hence metabolism in ruminant animals. The possible role of gut hormones in ruminants is discussed.
Journal of Endocrinology (1991) 129, 55–58
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ABSTRACT
Glucose utilization and production and changes in concentrations of plasma metabolites were studied in lactating and non-lactating sheep in response to three levels of insulin infusion whilst maintaining euglycaemia. Glucose utilization and production responded to insulin infusion similarly in both lactating and non-lactating ewes but, as circulating concentrations of insulin were lower in lactating animals, these parameters appeared more sensitive to plasma concentrations of insulin in lactating sheep. Changes in plasma concentrations of glycerol and free fatty acids during lactation indicated reduced sensitivity to insulin in adipose tissue and changes in plasma concentrations of amino acids were also less during lactation, suggesting reduced sensitivity of protein synthesis to insulin. Changes in plasma concentrations of urea and β-hydroxybutyrate during lactation were similar to those in non-lactating animals, indicating similar insulin sensitivity of hepatic metabolism. It is concluded that during lactation ovine adipose tissue and muscle are more resistant to increased concentrations of insulin but that the sensitivity of the sheep liver is unchanged or increased. The rate of removal of insulin from the circulation was higher in lactating animals.
Journal of Endocrinology (1990) 124, 59–66
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Search for other papers by J. P. McCarthy in
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ABSTRACT
Plasma concentrations of gastric inhibitory polypeptide (GIP) were measured in preruminant goat kids before and after consumption of milk, skimmed milk or solutions of milk fat, lactose, glucose or casein plus lactose. GIP concentrations increased significantly within 1 h of consumption of milk or milk fat, and were elevated for the remainder of the 5-h sampling period. The integrated mean change in GIP concentration during this period did not differ between these two meals. GIP levels were slightly increased above basal values 5 h after skimmed milk consumption, probably reflecting the absorption of a small amount of fat, but overall there was no significant GIP response to this or to any of the other test meals. The marked increase in GIP concentration after a milk feed indicates a physiological role for the hormone in preruminants but, in contrast to the situation in simple-stomached animals, carbohydrate absorption does not elicit GIP secretion in the preruminant goat. The data strongly suggest that fat is the major nutrient to stimulate GIP secretion in these animals.
Journal of Endocrinology (1993) 138, 167–173
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ABSTRACT
Plasma concentrations of gastric inhibitory polypeptide (GIP)-like activity were determined in sheep before and after refeeding following a 48-h fast. Plasma concentrations increased significantly after feeding, from about 250 pg/ml to about 550 pg/ml. Other metabolites in plasma also increased at this time, reflecting the absorption of nutrients from the gastrointestinal tract. Significant increases were observed in the plasma concentrations of acetate, β-hydroxybutyrate and triacylglycerol. By comparing the time-courses of the changes in concentration of GIP and other metabolites in plasma, possible sites of secretion and secretagogues of GIP in ruminant animals are proposed. The results demonstrate that GIP is secreted in response to nutrient absorption in adult ruminants and that, as in simple-stomached animals, the absorption of long-chain free fatty acids plays an important role in this secretion.
Journal of Endocrinology (1992) 134, 235–240
