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      Modulation of Growth Hormone-Releasing Factor Stimulated Growth Hormone Secretion by Plasma Glucose and Free Fatty Acid Concentrations in Sheep

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          Effects of plasma glucose and free fatty acid (FFA) concentrations on bovine growth hormone-releasing factor (bGRF)-induced release of growth hormone (GH) were examined in ovariohysterectomized sheep. In experiment 1, the effects of an infusion of insulin (0.025 U/kg BW·h<sup>–1</sup>), glucose (40 mg/kg BW·· h<sup>–1</sup>), insulin plus glucose or saline on the subsequent effects of bGRF on plasma GH concentrations were determined. Insulin-induced hypoglycemia inhibited GRF effects on plasma GH concentrations while glucose infusion enhanced bGRF actions. Infusing a higher glucose dose (120 mg/kg BW·h<sup>–1</sup>) had no effect on GRF actions. Subsequently, infusion of FFA (0.25 g/kg/·h<sup>–1</sup>), nicotinic acid (50 mg/kg BW) or saline for 1 h prior to bGRF injection demonstrated that FFA inhibited GRF actions but FFA depletion by nicotinic acid infusion had no effect on GRF actions. Nicotinic acid (40 mg/kg BW·h<sup>–1</sup>) infused for 2 h prior to bGRF injection significantly enhanced bGRF-stimulated GH secretion. Finally, to determine whether central nervous system glucopenia produced similar effects to insulin-induced hypoglycemia, 2-deoxyglucose (500 mg) was injected into the lateral ventricle followed in 1 h by the i.v. injection of bGRF. The central glucopenia produced by 2-DG inhibited GRF-stimulated GH release. These data demonstrate that decreased peripheral or central nervous system glucose availability and exogenous administration of FFA antagonized GRF-induced release of GH. And, pharmacologic depletion of circulating FFA for at least 2 h facilitated GRF-induced release of GH.

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          Author and article information

          S. Karger AG
          02 April 2008
          : 48
          : 6
          : 627-633
          Departments of aPhysiology and Pharmacology, and dAnatomy and Histology, College of Veterinary Medicine, and Departments of bAnimal Health Research and cAnimal and Dairy Sciences, Alabama Agricultural Experiment Station, Auburn University, Ala., USA
          125073 Neuroendocrinology 1988;48:627–633
          © 1988 S. Karger AG, Basel

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          Pages: 7
          Original Paper


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