Glucose and fat metabolism in adults with growth hormone deficiency

Adults with long-standing GH deficiency have a decreased lean body mass and an increased fat mass. We investigated the effects of the abnormal body composition on glucose turnover and fuel metabolism.

Cross-sectional analysis.

Twenty-four adults with acquired GH deficiency and a wide range of adiposity (body mass index from 18.8 to 42.3 kg/m2).

In the post-absorptive state glucose turnover was measured following intravenous injection of 3-3H-glucose and leucine oxidation was assessed following intravenous injection of 1-14C-leucine. Glucose and fat oxidation were calculated from indirect calorimetry using protein oxidation derived from leucine oxidation.

Total glucose turnover was 692 +/- 146 mumol/min (mean +/- SD) and increased with height (r = 0.70, P = 0.0003) and with lean body mass (LBM) (r = 0.80, P < 0.0001). Glucose turnover expressed per kg LBM was in the published normal range (14.2 +/- 2.1 mumol/kg LBM min). Glucose oxidation was 47 +/- 27% of glucose turnover and increased with LBM (r = 0.59, P = 0.008) but not with height (r = 0.32, NS). Glucose turnover increased with increasing fat oxidation (r = 0.61, P = 0.006). The non-oxidative part of glucose turnover was positively correlated with fat oxidation (r = 0.82, P = 0.0001) and inversely with the respiratory quotient (r = -0.81, P < 0.0001). Ketone body concentration (r = 0.55, P = 0.03), but not free fatty acid levels (r = 0.21, NS), correlated with fat oxidation. Fasting plasma glucagon levels were elevated (35 +/- 13 vs 9 +/- 19 pmol/l (published controls)) and inversely related to lean body mass (r = -0.44, P = 0.04).

Adults with GH deficiency studied after an overnight fast have changes in glucose and fuel metabolism seen in normal subjects after more prolonged fasting suggesting that adults with hormone deficiency have reduced carbohydrate stores.