MEASUREMENT OF INSULIN‐LIKE GROWTH FACTOR‐II BY RADIORECEPTOR ASSAY USING OVINE PLACENTAL MEMBRANES

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Abstract
A new radioreceptor assay for insulin-like growth factor-II (IGF-II), using receptors on ovine placental membranes, is described. Half-maximal displacement of specifically bound radioiodinated human IGF-II tracer was seen at 1.0 ng/tube of unlabelled IGF-II. The cross-reactivity of IGF-I was 1%, and insulin was entirely without effect. Measured on serum samples from 100 healthy adults, the mean IGF-II concentration (±SD) was 576 ± 160 ng/ml. Identical mean values were seen for all adult age groups up to 65 years. The mean value for 10 acromegalic adults was 583 ± 155 ng/ml, and for 9 GH-deficient subjects, 161 ± 26 ng/ml (P < 0.001 compared to normals). Of eight patients with chronic renal failure, none had an IGF-II level less than 2SD above the normal mean. No significant effect of renal dialysis was seen. In groups of patients with gastric, breast, lung, testicular, oat cell, ovarian, colonic and prostatic carcinoma, Hodgkin's lymphoma, non-Hodgkin's lymphoma, sarcoma and teratoma (5–12 patients per group), mean IGF-II levels were in the lower part of the normal range. Thus this study does not provide evidence supporting a role for excessive IGF-II production in the growth of any of these tumour types.