Effect of increased haemoglobin levels on growth hormone (GH) secretion in beta-thalassaemia major: differences between prepubertal subjects and patients with delayed puberty.

Basal and L-dopa-stimulated secretion of growth hormone (GH) was investigated in 10 patients with beta-thalassaemia major. Five patients were prepubertal (chronological age 8 to 12 years), whereas 5 patients had delayed puberty (chronological age 15 to 19 years). Ten normal prepubertal subjects (chronological age 8 to 11 years) served as the control group. Each thalassaemic patient was subjected to two L-dopa tests (0.5 g L-dopa plus 0.7 mg/Kg body weight propranolol, orally): one was performed under conditions of low haemoglobin (Hb) levels (30 days after the last blood transfusion), and the second in the presence of increased Hb concentrations (10 days after the transfusion of packed red blood cells). Before the transfusion of packed red blood cells, basal GH concentrations were significantly higher in the patients with delayed puberty (4.3 +/- 1.6 ng/ml), than in prepubertal thalassaemic (1.8 +/- 0.9 ng/ml, p less than 0.05) and control (1.9 +/- 1.0 ng/ml, p less than 0.02) subjects. In contrast, the pituitary responsiveness to L-dopa, expressed as the relative maximum response for GH (GH delta %), was significantly higher in the latter two groups (8.5-fold, p less than 0.05, and 10.9-fold, p less than 0.02, respectively). The transfusion of packed red blood cells increased significantly Hb concentrations in both groups of thalassaemic patients (prepubertal +27%, p less than 0.05, delayed puberty +33%, p less than 0.025, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)