GH Receptor Deficiency in Ecuadorian Adults Is Associated With Obesity and Enhanced Insulin Sensitivity.

CONTEXT

Ecuadorian subjects with GH receptor deficiency (GHRD) have not developed diabetes, despite obesity.

OBJECTIVE

We sought to determine the metabolic associations for this phenomenon.

DESIGN

Four studies were carried out: 1) glucose, lipid, adipocytokine concentrations; 2) metabolomics evaluation; 3) metabolic responses to a high-calorie meal; and 4) oral glucose tolerance tests.

SETTING

Clinical Research Institute in Quito, Ecuador.

SUBJECTS

Adults homozygous for the E180 splice mutation of the GH receptor (GHRD) were matched for age, gender, and body mass index with unaffected control relatives (C) as follows: study 1, 27 GHRD and 35 C; study 2, 10 GHRD and 10 C; study 3, seven GHRD and 11 C; and study 4, seven GHRD and seven C.

RESULTS

Although GHRD subjects had greater mean percentage body fat than controls, their fasting insulin, 2-hour blood glucose, and triglyceride levels were lower. The indicator of insulin sensitivity, homeostasis model of assessment 2%S, was greater (P < .0001), and the indicator of insulin resistance, homeostasis model of assessment 2-IR, was lower (P = .0025). Metabolomic differences between GHRD and control subjects were consistent with their differing insulin sensitivity, including postprandial decreases of branched-chain amino acids that were more pronounced in controls. High molecular weight and total adiponectin concentrations were greater in GHRD (P = .0004 and P = .0128, respectively), and leptin levels were lower (P = .02). Although approximately 65% the weight of controls, GHRD subjects consumed an identical high-calorie meal; nonetheless, their mean glucose concentrations were lower, with mean insulin levels one-third those of controls. Results of the 2-hour oral glucose tolerance test were similar.

MAIN OUTCOME MEASURES

Measures of insulin sensitivity, adipocytokines, and energy metabolites.

CONCLUSIONS

Without GH counter-regulation, GHRD is associated with insulin efficiency and obesity. Lower leptin levels, despite higher percentage body fat, suggest that obesity-associated leptin resistance is GH dependent. Elevated adiponectin levels not correlated with percentage body fat indicate that GH signaling is necessary for their typical suppression with obesity.