IGF-1 levels, GH peak after GHRH+Arginine and 24h-GH-profile in males with the metabolic syndrome

Abdominal obesity and insulin resistance are central findings in the metabolic syndrome. The metabolic syndrome leads to similar symptoms of growth hormone deficiency (GHD), such as increased body fat mass and decreased lean body mass, disorders of glucose and lipid metabolism. The aim of the present study was to evaluate parameters of GH/IGF-1 axis in patients with the metabolic syndrome and its correlation with characteristic parameters of the metabolic syndrome, such as BMI, waist circumference, abdominal fat mass, fasting plasma glucose (FPG) and glucose disposal rate (GDR). The study group consisted of 25 males with the metabolic syndrome (age 55±5 yr, BMI 33.4±2.8kg/m 2 , FPG 121±24mg/dL; mean±S.D.). The mean IGF-1 level was 140+47µg/L and GH peaks after GHRH plus arginine (GHRH/ARG) ranged from 1.2 to 15.9µg/L (6.1±3.5µg/L) and were below 5µg/L in 10 males. 24h-GH-secretion correlated with IGF-1 levels (p=<0.0001, r2=0.6). 22/25 (88%) showed a GH response <9µg/L. IGF-1 (p=0.003, r2=0.34) and the mean 24h-GH-secretion (p=0.01, r2=0.32) correlated with the GH peak after GHRH/ARG. The BMI correlated with GH peak after GHRH/ARG (p=0.01, r2=0.21), with the mean 24h-GH-secretion (p=0.02, r2=0.24) and with the IGF-1 levels (p=0.001, r2=0.27). Furthermore, waist circumference correlated with GH peak after GHRH/ARG (p=0.01, r2=0.21), with the mean 24h-GH-secretion (p=0.02, r2=0.25) and with the IGF-1 (p=0.02, r2=0.21). We have seen a trend of correlation between IGF-1 and the abdominal fat mass (p=0.059, r2=0.15). Moreover, we have seen a weak but not significant correlation between GDR and GH peak after GHRH/ARG (p=0.06, r2=0.54). The mean 24h-cortisol-secretion was 224±54 nmol/l and did not correlate with the GH peak after GHRH/ARG (p=0.54, r2=0.1). In conclusion, GH/IGF-1 axis is blunted in patients with the metabolic syndrome. BMI and waist circumference are strong parameters correlating with a diminished somatotropic function. Obesity decreases GH secretion and consequently shares many symptoms of untreated GHD.