ERYTHROCYTOSIS AFTER RENAL-TRANSPLANTATION REPRESENTS AN ABNORMALITY OF INSULIN-LIKE GROWTH-FACTOR-I AND ITS BINDING-PROTEINS

Background Secondary erythrocytosis is classically defined by an incre ase in erythropoietin (EPO) production. Despite increased levels of EP O often seen in secondary erythrocytosis, some of these forms such as that seen after renal transplantation remain undefined. Our group has recently investigated the in vivo function of insulin-like growth fact or-I (IGF-I) in erythropoiesis both in humans and in a murine model of chronic renal failure. These data, and the recently recognized role o f IGF-I in polycythemia vera, suggested that IGF-I might be involved i n secondary erythrocytosis. Methods. Renal transplant recipients who d eveloped erythrocytosis after transplantation were compared to normal individuals and to renal transplant recipients without erythrocytosis, We measured fasting serum EPO and IGF-I in all three groups. Because binding proteins may modify IGF-I function, IGF-I-binding proteins (IG FBP) 1 and 3, major binding proteins of IGF-I, were also measured. Res ults. Renal transplant recipients have significantly elevated serum of IGF-I and IGFBP3 compared to normal individuals, When transplant reci pients with and without posttransplant erythrocytosis were compared, s imilar levels of IG;F-I were found; however, the group with erythrocyt osis had significantly elevated IGFBP1 and IGFBP3, No other significan t differences including EPO levels were found between the groups. Conc lusions. Erythrocytosis after renal transplantation represents an anom aly of both IGF-I and its major binding proteins. Further studies are under way to better define this dysregulation and determine whether IG F-I can play a more generalized role in secondary forms of erythropoie sis.