Elevated serum human growth hormone and decreased serum insulin in prediabetic males after intravenous tolbutamide and glucose

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Abstract
Serum human growth hormone (HGH), serum immunoreactive insulin (IRI), plasma free fatty acids, and blood glucose were measured during intravenous glucose and intravenous tolbutamide tolerance tests in 13 normal and 13 prediabetic (offspring of two diabetic parents) males, closely matched for weight and age. Only prediabetics with normal glucose tolerance during oral, intravenous, and cortisone-primed glucose tolerance tests were evaluated. Mean serum HGH levels were significantly higher in prediabetics in response to intravenous tolbutamide and at the end of the 3-hr intravenous glucose tolerance tests (IVGTT). This is interpreted as a hyperresponsiveness of the growth hormone-releasing mechanisms in prediabetic subjects. The insulin response during the first 10 min of an IVGTT was significantly reduced in prediabetic males as compared to normal controls, whereas the insulin response to intravenous tolbutamide was not significantly different at the same time intervals in the same subjects.It appears, therefore, that measuring IRI during an IVGTT can be valuable in detecting the earliest signs of diabetes even before any disturbance of blood glucose homeostasis is seen. The possibility that growth hormone hypersecretion in prediabetics might play a role in the pathogenesis of human diabetes mellitus is discussed.