Insulin and glucagon responses to provocation with glucose and arginine in prepubertal children with thalassemia major before and after long-term blood transfusion.

Abstract

Hypertransfusion therapy has dramatically increased the duration and quality of life in patients with B-thalassemia major; however, it leads to chronic iron overload, and is frequently complicated by the development of diabetes mellitus or impaired glucose tolerance. To determine the early effect of iron overload on the endocrine pancreatic function, we studied glucose, insulin, and glucagon responses to oral load of glucose and to arginine provocation in 15 children with B-thalassemia major, before and after (3.1 +/- 0.6 years) high-transfusion and iron chelation and compared them with 15 age matched normal controls. In addition, we evaluated growth hormone (GH) responses to oral clonidine and measured the circulating insulin-like growth factor-I concentration in thalassemic children on long-term transfusion and controls. After long-term high-transfusion, thalassemic children had significantly decreased serum insulin concentrations and low insulin/glucose ratios at 60 and 120 min after an oral glucose load (1.75 g/kg) in comparison with values before therapy and those for controls. None of the thalassemic children had glucose intolerance after this period of frequent blood transfusion; however, their serum glucose levels at 60 and 120 min after the oral glucose load were significantly higher compared to control children. Thirty minutes after starting arginine infusion, serum insulin concentration was significantly lower in thalassemic children compared to before therapy. Basal and arginine-stimulated glucagon secretions were significantly elevated in thalassemic children on long-term blood transfusion with significantly low serum insulin/glucagon ratios. In addition, the high basal serum glucagon concentrations were not suppressed after the oral glucose load. Despite hyperglucagonaemia in all thalassemic children, their blood glucose dropped appropriately below 50 per cent of the fasting glucose level after an intravenous insulin dose (0.1 U/kg) ruling out any significant insulin-resistance. GH responses to clonidine provocation were subnormal in thalassemic children after long-term blood transfusion compared to controls. In summary, thalassemic children on long-term blood transfusion and iron chelation have progressive and early loss of B-cell mass, manifested by decreased insulin release in response to secretagogues, before the development of significant insulin resistance or impairment of glucose tolerance.