Growth hormone response to arginine administration in diabetics--with special reference to the multiple regression analysis in association with diabetic retinopathy

Abstract

In 107 patients with non-insulin dependent diabetes(NIDDM), plasma growth hormone(GH) responses during standard arginine test (0.5 g/kg of body weight) were studied and analyzed in comparison with those in 17 normal subjects. The indices of the responsiveness of GH, peak value of GH, sum of GH values(sigma GH), area of GH curve(integral of GH), sum of GH values above fasting level(sigma delta GH) and area of GH curve above fasting level(integral of delta GH) during the test (2 hr) were calculated. Data were also analyzed with multiple regression analysis using stepwise method for variable selection. Basal level of GH was significantly higher in diabetic patients than in normal subjects (2.1 +/- 1.7 vs. 1.6 +/- 0.5 ng/ml, mean +/- SD, p less than 0.05), and sigma GH and integral of GH were also higher in diabetic patients. There was a significantly positive correlation between fasting plasma glucose(FPG) and basal level of GH (r = 0.24, n = 107, p less than 0.05), and the indices of GH responses except delta GH and GH peak value (r = 0.24 to 0.31, p less than 0.05 to 0.01). Some indices of GH responses (sigma delta GH, sigma GH, integral of delta GH and integral of GH) were significantly higher in the poor control group (patients with FPG above 180 mg/dl, n = 29) of diabetic patients than in the good control group (patients with FPG below 140 mg/dl, n = 59), or in the group with no abnormal findings of retinopathy (n = 46). During the follow-up of retinopathy for 2.5 years on the average, progression of retinopathy was found in 21 out of 107 patients. Significantly higher GH, and GH in the patients with increasing severity of retinopathy were revealed retrospectively compared to the patients without it. However, there were no significant differences in these parameters between both groups matched by FPG or severity of retinopathy. Multiple regression analysis to the basal GH level and GH responses during arginine infusion as criterion variables of various predictor variables (total 44 factors: biochemical laboratory data, indices of glucose and insulin response to oral glucose load, indices of glucose response to arginine, age, age of the onset, obese index, duration of retinopathy, neuropathy, and therapy) were performed in 86 patients using forward and backward method for variable selection. Basal plasma level of GH showed close positive association with therapy and proteinuria and negative association with age and obesity. Five of 6 indices of GH responsiveness showed significant relationship with retinopathy.(ABSTRACT TRUNCATED AT 400 WORDS)