Effects of GH in human muscle and fat.

Skeletal muscle is the major constituent of lean body mass and a major determinant of energy expenditure both at rest and during physical activity. Growth hormone, in turn, influences muscle mass as well as energy expenditure. Growth hormone substitution in adults increases muscle mass by 5-10%, but part of the effect is attributed to rehydration rather than protein accretion. In addition, GH regulates substrate metabolism in muscle and in particular antagonizes insulin-stimulated glucose disposal. This effect is linked to increased free fatty acid (FFA) flux but the molecular mechanisms remain unclear. During fasting, GH-induced insulin resistance may be favorable by reducing the demand of gluconeogenesis from protein. But in the postprandial phase, GH exposure may compromise glucose tolerance via the same mechanisms. Understanding the mechanisms whereby GH antagonizes insulin-stimulated glucose disposal in muscle is an important future research field with implications for a variety of clinical conditions ranging from malnutrition to obesity and type 2 diabetes.

Conventional and novel biomarkers of treatment outcome in patients with acromegaly: discordant results after somatostatin analog treatment compared with surgery.

CONTEXT: Control of disease activity in acromegaly is critical, but the biochemical definitions remain controversial. OBJECTIVE: To compare traditional and novel biomarkers and health status in patients with acromegaly treated with either surgery alone or somatostatin analog (SA). DESIGN AND METHODS: Sixty-three patients in long-term remission based on normalized total IGF1 levels after surgery alone (n=36) or SA (n=27) were studied in a cross-sectional manner. The groups were comparable at diagnosis regarding demographic and biochemical variables. Each subject underwent 3 h of serum sampling including a 2-h oral glucose tolerance test (OGTT). Health status was measured by two questionnaires: EuroQoL and Acrostudy (Patient-assessed-Acromegaly symptom questionnaire (PASQ)). RESULTS: Total and bioactive IGF1 (µg/l) levels were similar (total: 185 ± 10 (SA) versus 171 ± 8 (surgery) (P=0.28); bioactive: 1.9 ± 0.2 vs 1.9 ± 0.1 (P=0.70)). Suppression of total and free GH (µg/l) during OGTT was blunted in the SA group (total GH(nadir): 0.59 ± 0.08 (SA) versus 0.34 ± 0.06 (surgery) (P=0.01); free GH(nadir): 0.43 ± 0.06 vs 0.19 ± 0.04 (P<0.01)). The insulin response to OGTT was delayed, and the 2-h glucose level was elevated during SA treatment (P=0.02). Disease-specific health status was better in patients after surgery (P=0.02). CONCLUSIONS: i) Despite similar and normalized IGF1 levels, SA treatment compared with surgery alone was associated with less suppressed GH levels and less symptom relief; ii) this discordance may be due to specific suppression of hepatic IGF1 production by SA; iii) we suggest that biochemical assessment during SA treatment should include both GH and IGF1.