Effect of Increased Haemoglobin Levels on Growth Hormone (GH) Secretion in β-Thalassaemia Major: Differences between Prepubertal Subjects and Patients with Delayed Puberty

Summary

Basal and L-dopa-stimulated secretion of growth hormone (GH) was investigated in 10 patients with β-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 < 0.05) and control (1.9 ± 1.0 ng/ml, p < 0.02) subjects. In contrast, the pituitary responsiveness to L-dopa, expressed as the relative maximum response for GH (GH Δ%), was significantly higher in the latter two groups (8.5-fold, p < 0.05, and 10.9-fold, p < 0.02, respectively). The transfusion of packed red blood cells increased significantly Hb concentrations in both groups of thalassaemic patients (prepubertal +27%, p < 0.05, delayed puberty +33%, p < 0.025, respectively). In the patients with delayed puberty the rise in Hb levels decreased significantly the basal GH secretion (1.9 ± 0.8 ng/ml, p < 0.05) and restored the pituitary responsiveness to L-dopa (+8.5-fold, p < 0.05), whereas no significant changes were observed in prepubertal thalassaemic subjects. A decrease in somatomedin generation, along with some functional hypothalamic derangement, could explain these results.

Key words

β-Thalassaemia major - Growth hormone - Delayed puberty - L-dopa test - Haemoglobin levels