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.
Sartin
J L
JL
Department of Physiology, College of Veterinary Medicine, Auburn University, Ala.
Bartol
F F
FF
Kemppainen
R J
RJ
Dieberg
G
G
Buxton
D
D
Soyoola
E
E
D000818:Animals; D001786:Blood Glucose / Q000032:analysis*; D005230:Fatty Acids, Nonesterified / Q000008:administration & dosage / Q000097:blood*; D005260:Female; D005947:Glucose / Q000494:pharmacology; D013006:Growth Hormone / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D007003:Hypoglycemia / Q000139:chemically induced; D007044:Hysterectomy; D007328:Insulin / Q000097:blood / Q000494:pharmacology; D009525:Niacin / Q000494:pharmacology; D010052:Ovariectomy; D012756:Sheep
D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D007328:Insulin; D009525:Niacin; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; D005947:Glucose