Reduced growth hormone secretion improves insulin sensitivity in adolescent girls with type 1 diabetes

The aims of the present study were to compare nocturnal growth hormone (GH) secretion, insulin requirements and insulin sensitivity on two occasions in six adolescent girls with type 1 diabetes when the GH secretion was reduced one night by an oral dose of 100 mg of pirenzepine at bedtime. The mean nocturnal intravenous insulin infusion required to maintain a normal constant blood glucose concentration between 24:00 and 07:00 was 53% higher during the night on placebo (p = 0.0212). During the night on pirenzepine, the serum GH area under the curve (AUG) was reduced in all patients to a mean concentration which was 50.1% (15-78%) of that during the night without pirenzepine (p = 0.0036). The nocturnal urinary GH excretion was also reduced in all of the investigated patients (p = 0.0229). Insulin sensitivity in the morning, measured by the euglycaemic hyperinsulinaemic glucose clamp, increased significantly from 115 +/- 51 mg m(-2) min(-1) after the night on placebo to 205 +/- 67 mg m(-2) min(-1) after the night on pirenzepine (p = 0.0161). No side-effects were observed during the pirenzepine night. Negative correlations were found between the nocturnal serum GH AUC and the insulin-stimulated glucose metabolism (r = -0.65, p = 0.0241) and between the nocturnal urinary GH excretion and the insulin-stimulated glucose metabolism (r = -0.77, p = 0.0054). In conclusion, the present study shows a relation between GH secretion and insulin resistance in adolescent girls with type 1 diabetes. The administration of pirenzepine acutely reduces GH secretion and improves insulin sensitivity.