STUDY ON GROWTH-HORMONE AND INSULIN-SECRETION IN MYOTONIC-DYSTROPHY

Growth hormone (GH) levels were measured in 12 patients with myotonic dystrophy (MD; 7 men and 5 women, aged 21-49 years) and 14 volunteers after administration of 100 mu g GH-releasing hormone (GHRH; 1-29). A 75-g oral glucose tolerance test was carried out to determine glucose, insulin, plasma C-peptide, and urinary C-peptide. The GH level in six MD patients responded normally to GHRH (group I), with a peak of 17.1 +/-1.46 mu g/l, compared with controls (27.8+/-19.6 mu g/l, NS), and t hat in the other six patients responded subnormally, with a peak of 3. 15+/-1.46 mu g/l, lower than in controls and in group I patients (P < 0.001). In group I the insulin response to the glucose tolerance test showed hyperinsulinism and was lower than that in group II patients; s timulated C-peptide was also higher in group II than in group I and in controls; urinary C-peptide levels were parallel to those in previous data. In all MD patients there were a negative correlation between ab solute values of GH response to GHRH and insulin response to glucose t olerance test (r = -0.79, P < 0.001). Our data suggest that the failur e in GH release and peripheral insulin action is due to a generalized defect in cellular membrane function in MD patients.