Modulation of growth hormone-releasing factor stimulated growth hormone secretion by plasma glucose and free fatty acid concentrations in sheep.
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-1), glucose (40 mg/kg BW.h-1), 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-1) had no effect on GRF actions. Subsequently, infusion of FFA (0.25 g/kg/.h-1), 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-1) 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 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.[1]References
- Modulation of growth hormone-releasing factor stimulated growth hormone secretion by plasma glucose and free fatty acid concentrations in sheep. Sartin, J.L., Bartol, F.F., Kemppainen, R.J., Dieberg, G., Buxton, D., Soyoola, E. Neuroendocrinology (1988) [Pubmed]
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