ABDOMINAL FAT DETERMINES GROWTH HORMONE-BINDING PROTEIN-LEVELS IN HEALTHY NONOBESE ADULTS

The circulating high affinity GH-binding protein (GHBP), which derives from the extracellular domain of the hepatic GH receptor, correlates inversely to GH levels and directly to body mass index (BMI) in health y adults. As GH secretion and adiposity are also interrelated, we test ed the hypothesis that body composition, more than GH, determines GHBP levels in healthy adults. Forty-two healthy adults [21 females and 21 males; mean age, 39.4 yr range, 27-59 yr); mean BMI, 23.9 kg/m(2) (ra nge, 18.9-34.7 kg/m(2))], underwent anthropometric measurements (BMI, W/H ratio, computed tomography scan, dual energy x-ray absortiometry ( DEXA) scan, and bioimpedance) in addition to two GH stimulation tests (arginine and clonidine) and a 24-h GH profile. By simple linear regre ssion, serum GHBP correlated positively to several indices of adiposit y: intraabdominal fat (r = 0.537; P = 0.001), sc abdominal fat (r = 0. 680; P < 0.001), BMI = 0.483; P = 0.001), W/H ratio (r = 0.452; P = 0. 003), total body fat (DEXA scanning; r = 0.503; P = 0.002), and body f at (bioimpedance; r = 0.354; P = 0.023). Lean body mass estimated by D EXA scan was negatively associated with GHBP (r = 0.541; P < 0.001). G HBP was inversely proportional to arginine-stimulated GH release (r = -0.346; P = 0.027) and negatively associated with several measures of spontaneous GH release as estimated by deconvolution analysis (GH mass , GH production rate, and mean GH; r = -0.371; P = 0.017, r = -0.393; P = 0.011, and r = -0.343; P = 0.028, respectively)). With multiple li near regression analyses, indices of adiposity were significant determ inants of GHBP levels, whereas GH status did not contribute independen tly to the prediction of GHBP. Neither insulin-like growth factor I no r fasting insulin levels correlated to GHBP levels. In conclusion, GHB P levels in normal adults seem to be determined by abdominal fat mass rather than GH secretion.