Long-term monitoring of insulin sensitivity in growth hormone-deficient adults on substitutive recombinant human growth hormone therapy.

Since the effects of recombinant human growth hormone (rhGH) replacement therapy on glucose metabolism are still a matter of debate, the aim of the present study was to evaluate the impact of long-term rhGH treatment on insulin sensitivity. Simple indices of insulin resistance (IR) and insulin sensitivity (IS), based on fasting glucose and insulin, such as the homeostasis model assessment of insulin resistance (HOMA-IR) and the quantitative insulin check index (QUICKI), were used to estimate the degree of IR and IS in 20 normoglycemic patients (11 men and 9 women; mean age, 44 +/- 14 years) with severe adult-onset GH deficiency (GHD). Measurements were determined at baseline and after 1 and 5 years of continuous rhGH therapy. Basal values were compared to those obtained in 20 healthy sex- and age-matched controls. Starting rhGH dose ranged from 3 to 8 microg/kg/d in keeping with sex and age, then doses were titrated according to insulin-like growth factor-I (IGF-I) levels. At baseline all patients had low IGF-I levels (10 +/- 5.4 nmol/L), high body mas index (BMI; 27.5 +/- 4 kg/m(2)), and elevated body fat percentage (BF%; 31.8 +/- 9.6). Fasting glucose and insulin levels, as well as HOMA-IR and QUICKI, did not differ significantly from those recorded in the control group. After 1 year of rhGH replacement therapy, normalization in IGF-I levels and a significant reduction in BF% were observed (P <.001), and these effects were maintained after 5 years of treatment. Fasting glucose increased from 79 +/- 10 to 87 +/- 13, and 87 +/- 12 mg/dL (P <.05) after 1 and 5 years of therapy, respectively. Fasting insulin significantly increased after 1 year, without further modifications in the long-term follow-up. HOMA-IR significantly increased from 2.1 +/- 1.7 to 2.5 +/- 1.7 (P <.05) after 1 year, then decreased to 2.3 +/- 1.5 (P = not significant [NS] v basal) after 5 years. A specular decrease in QUICKI from 0.37 +/- 0.05 to 0.34 +/- 0.03 (P <.01) occurred after 1 year, with a trend to increase (0.35 +/- 0.04; P = NS v basal) after 5 years. No patient developed impaired fasting glucose. In conclusion, rhGH therapy determined an increase in fasting glucose and insulin levels, causing in the short-term period a worsening of IS. The sustained reduction in BF%, without further deterioration of IS, suggests that long-term beneficial effects on body composition may overcome the negative influence of GH on glucose metabolism.