Effect of sustained hyperglycemia on GHRH induced GH secretion in man

Effect of sustained and severe hyperglycemia (greater than 200 mg/dl) on GHRH induced GH secretion was studied in 9 healthy volunteers who received GHRH (1 microgram/kg/BW, iv) during either saline or dextrose infusions which were started 2 hours before testing. During the latter, plasma glucose concentration plateaued at 303 mg/dl +/- 82 (mean +/- SD, range 200-450 mg/dl). Hyperglycemia resulted in a 57% decrease of peak plasma GH concentration: 9.3 +/- 4 vs 21.8 +/- 12 ng/ml (P less than 0.05). Two subjects had no change in GHRH induced plasma GH rise during hyperglycemia. No correlation was found between plasma glucose or insulin concentrations and percentage change in GHRH induced GH secretion. These data suggest that: 1) inhibition by hyperglycemia of GHRH induced GH secretion in non-diabetic subjects is neigter complete nor constant; 2) plasma glucose levels cannot predict the magnitude of the inhibition.