[Studies on plasma insulin-like growth factor (IGF)-I levels in normal subjects and in patients with various endocrine and metabolic diseases using radioimmunoassay for synthetic IGF-I (26-46)].

Determination of plasma IGF-I concentrations is not easily accessible to clinical use at present because of extremely limited supply of purified natural IGF-I essential for its assay system. Thus, an alternative method has recently been introduced by the development of a specific radioimmunoassay (RIA) for IGF-I (26-46). We examined the specificity and sensitivity of this assay system, and then investigated the changes in plasma concentrations of IGF-I in normal children, adults and in patients with various endocrine and metabolic diseases. Each plasma sample was subjected to acid-ethanol treatment before assay to separate IGF-I from its binding protein. The recovery rate of known amount of IGF-I (26-46) added to untreated plasma sample was more than 90%. The coefficients of variation of intra- and interassay were 9.0% and 13.6%, respectively. This assay system was able to detect IGF-I as low as 10 pg/tube. When plasma sample of a patient with active acromegaly was applied to Sephadex G-75 column, immunoreactive IGF-I was eluted at the position of 7,000 molecular weight. An inhibition curve of plasma extract from an acromegalic patient was parallel to that of IGF-I (26-46), indicating that the RIA could detect IGF-I. There was no remarkable difference between IGF-I values of plasma and serum from the same individual. The value of IGF-I concentration of cord plasma was considerably low (144 +/- 6.7 pg/ml, M +/- SEM) as compared with that of sera of 49 normal children aged 7-12 12 years (320 +/- 14.3 pg/ml). The highest value (460 +/- 54 pg/ml) was attained at the age of 13 years, followed by gradual decrease toward adult age. Plasma IGF-I concentration of normal adults between 20 and 69 years of age was 290 +/- 10 pg/ml. When plasma IGF-I values of adult males and females were separately plotted against age group of each decade, the value declined gradually with age in males while in females there was a remarkable increase in plasma IGF-I concentration at 4th and 5th decades, suggesting the effect of hormonal change at menopause on plasma IGF-I levels. There was a good correlation between disorders of GH secretion and plasma IGF-I concentrations. In 10 cases of active acromegaly the level was 506 +/- 67 pg/ml (285-970 pg/ml). On the other hand in 20 patients with pituitary dwarfism it was only 180 +/- 15 pg/ml.(ABSTRACT TRUNCATED AT 400 WORDS)