Growth hormone responses to growth-hormone-releasing hormone and thyrotropin-releasing hormone in diabetic patients with and without retinopathy

Abstract

Growth hormone (GH) responses to growth-hormone-releasing hormone (GRH) and thyrotropin-releasing hormone (TRH) were studied in 17 diabetic patients. Ten patients (group 1) had retinopathy corresponding to stage III-V (Scott's classification), and the remaining seven patients (group 2) had no retinopathy despite longer duration of diabetes in comparison with the patients in group 1. There were no differences in age, percent of ideal body weight, and serum HbA1 levels between the two groups. Basal serum GH levels were 1.9 ± 0.4 ng/ml (mean ± SEM) in group 1, and not different from the values in group 2 (1.6 ± 0.7 ng/ml). However, GH responses to synthetic human GRH-44 (1 μg/kg body wt, i.v. bolus) were significantly greater in group 1, as judged by the maximal response or integrated GH secretion after the administration of GRH. There were no differences in serum insulin-like growth factor I (IGF-I) levels between group 1 (262 ± 35 ng/ml) and group 2 (232 ± 30 ng/ml), and no significant correlation was found between serum IGF-I levels and GH responses to GRH in either of the two groups. Paradoxical GH responses to TRH (500 μg, i.v. bolus) were found in only one patient in each group. We have thus demonstrated that GH responses to GRH are more pronounced in diabetic patients with retinopathy than in patients without this complication, although it remains to be determined whether or not greater GH responses to GRH are causally related to the development of diabetic retinopathy.