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  • Author: Giuseppe Pizzocolo x
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Andrea Giustina, Simonetta Bossoni, Corrado Bodini, Antonino Cimino, Giuseppe Pizzocolo, Maurizio Schettino and William B. Wehrenberg

Abstract.

We evaluated the effects of iv pretreatment with exogenous GH on the GH response to GHRH either alone or in combination with pyridostigmine in 14 Type I diabetic patients and 6 normal subjects. All the subjects received an iv bolus injection of biosynthetic human GH, 2 IU; 2 h later they received either a. pyridostigmine, 120 mg orally, or b. placebo, 2 tablets orally, followed 1 h later by iv injection of GHRH(1-29) NH2, 100 μg. In normal subjects the median GH peak after GH+GHRH was 1.8, range 1.2-6.9 μg/l. Pyridostigmine enhanced the GH response to GHRH in all subjects. The median GH peak after pyridostigmine+ GH+GHRH was 32.7, range 19.8-42.1 μg/l (p<0.001 vs GHRH alone). Seven diabetic subjects had median GH peaks after GH+GHRH >6.9 μg/l (the maximum GH peak after GH+GHRH in normal subjects) (group A: median GH peak 35.7, range 21.7-55 μg/l). The other diabetic subjects had GH peak lower than 6.9 μg/l (group B: median GH peak 4.4, range 2.1-6.5 μg/l). Pyridostigmine significantly increased the GH response to GHRH in group B patients (median GH peak 29.3, range 15.7-93.4 μg/l, p<0.001 vs GH+GHRH alone), but not in group A patients (median GH peak 39.9, range 21.9-64.9 μg/l). Group A diabetic patients were younger and had higher HbA1c and blood glucose levels than group B patients. In those diabetic patients with an exaggerated GH response to GH+GHRH, pyridostigmine failed to cause the increase in GH secretion observed in diabetic and control subjects with no responses to GH+GHRH. It can be suggested that elevated 24-h GH levels in some Type I diabetic patients may be due to decreased somatostatinergic tone which in turn causes altered autoregulation of GH secretion. We hypothesize that this finding is a consequence of a reset of the hypothalamic control of GH secretion caused by a chronically elevated blood glucose level in this subpopulation.