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.

Recombinant hGH replacement therapy and the hypothalamus-pituitary-thyroid axis in children with GH deficiency: when should we be concerned about the occurrence of central hypothyroidism?

OBJECTIVE: Recombinant hGH treatment may alter thyroid hormone metabolism and we have recently reported that 50% of patients with GH deficiency (GHD) due to organic lesions, previously not treated with thyroxine, developed hypothyroidism during treatment with recombinant human GH (rhGH). These results prompted us to evaluate the impact of rhGH treatment on thyroid function in children with GHD. DESIGN: Open study of GH treatment up to 12 months. Investigations were performed at baseline, and after 6 and 12 months of GH therapy. MEASUREMENT AND STUDY SUBJECTS: Serum TSH, FT4, FT3, AbTg and AbTPO, IGF-I, height and weight, were evaluated in 20 euthyroid children (group A) with idiopathic isolated GHD and in six children (group B) with multiple pituitary hormone deficiencies (MPHD) due to organic lesions. Among the latter, four already had central hypothyroidism and were on adequate LT4 replacement therapy, while two were euthyroid at the beginning of the study. RESULTS: Serum IGF-I levels normalized in all patients. In both groups, a significant reduction in FT4 levels (P < 0.01) occurred during rhGH therapy. No patient in group A had FT4 values into the hypothyroid range, while in four of six patients in group B, fell FT4 levels into the hypothyroid range during rhGH. In particular, the two euthyroid children developed central hypothyroidism during rhGH treatment, and their height velocities did not normalize until the achievement of euthyroidism through appropriate LT4 substitution. No variation in serum FT3 and TSH levels was recorded in either groups. CONCLUSION: Contrary to that observed in patients with MPHD, rhGH replacement therapy does not induce central hypothyroidism in children with idiopathic isolated GHD, further supporting the view that in children with MPHD, as in adults, GHD masks the presence of central hypothyroidism. Slow growth (in spite of adequate rhGH substitution and normal IGF-I levels) is an important clinical marker of central hypothyroidism, therefore a strict monitoring of thyroid function is mandatory in treated children with MPHD.

Recombinant human GH replacement therapy and thyroid function in a large group of adult GH-deficient patients: when does L-T(4) therapy become mandatory?

The effect on thyroid function of GH administration to 66 adult patients with severe GH deficiency was studied. Seventeen patients were euthyroid, and 49 had central hypothyroidism and were adequately treated with L-T(4). Forty patients were assigned to a low recombinant human GH (rhGH) regimen (3 microg/kg body wt.d for 3 months followed by 6 microg/kg body wt.d for another 3 months) and 26 to a higher one (6 microg/kg body wt.d for 3 months followed by 12 microg/kg body wt.d for another 3 months). Serum IGF-I, TSH, free T(4) (FT(4)), free T(3) (FT(3)), reverse T(3), T(4)-binding globulin, and antithyroid autoantibody (TgAb and TPOAb) were measured in basal condition and after 3 and 6 months of therapy. Normalization of IGF-I levels was obtained after 6-month rhGH treatment in 67% of patients, independently from the dose, whereas a significant reduction in FT(4) and reverse T(3) levels was recorded (P < 0.01), without variations in all the other parameters studied, including serum TSH, FT(3), and T(4)-binding globulin circulating levels. Antithyroid autoantibodies were detected in 11 of 66 patients (16.6%). Eight of 17 (47%) euthyroid subjects and 9 of 49 (18.3%) central hypothyroid patients, despite adequate substitution at baseline, showed FT(4) levels under the normal range at the end of the study. Altogether, 17 of 66 patients (25.7%) worsened their thyroid function. This study shows that GH deficiency masks in a consistent number of adult patients a state of central hypothyroidism. Therefore, during rhGH treatment, a careful monitoring of thyroid function is mandatory to start or adjust L-T(4) substitutive therapy.