Radioimmunoassay for insulin-like growth factor II (IGF-II)

Abstract

Insulin-like growth factor II (IGF-II) levels in human plasma were measured in physiological and pathological conditions by radioimmunoassay (RIA) with biosynthetic IGF-II. This RIA was specific for IGF-II and cross-reactivity with IGF-I was 1%. The sensitivity was 15 pg/tube with 50% displacement at 50 pg/tube. The intra- and inter-assay coefficients of variation for IGF-II were 6.3 and 9.3%, respectively. The plasma IGF-II levels in normal adults, patients with hypopituitarism and patients with active acromegaly were 589.6 ± 15.8, 800.9 ± 45.6 and 330.3 ± 24.3 ng/ml, respectively. After human growth hormone (hGH) treatment in hypopituitarism, IGF-II slightly increased, but not significantly. After adenectomy in patients with acromegaly, IGF-II significantly decreased. These data indicate that IGF-II concentrations in plasma were partially GH dependent. This GH dependency was less than that of IGF-I. IGF-II was low in patients with anorexia nervosa and with liver cirrhosis and high in patients with renal failure. In two cases with extrapancreatic tumor-associated hypoglycemia, plasma IGF-II was increased to 1123.8 and 843.5 ng/ml, and returned to normal after tumor resection. These data showed that IGF-II was partly dependent on GH and nutritional conditions and that IGF-II was the most likely cause of some cases of hypoglycemia with extrapancreatic tumor. This specific and sensitive RIA of IGF-II would be useful in evaluating its physiological and pathological role in plasma and tissue.