Clinical application of serum insulin-like growth factor I (IGF-I)(26-46) radioimmunoassay--with special reference to the relationship between IGF(26-46) and growth hormone secretion

Abstract

Serum insulin-like growth factor I(IGF-I)(26-46) levels were determined in normal children aged 0-16y(n = 111), adults(n = 11), and various diseased conditions. In order to elucidate a mutual relationship between IGF-I(26-46) and growth hormone (GH) secretion, the following correlations were evaluated: 1) a correlation between IGF-I(26-46) and basal GH level (n = 57), 2) a correlation between IGF-I(26-46) and GH level responding to the insulin tolerance test (ITT) (n = 30), 3) a correlation between IGF-I(26-46) and an integrated concentration of GH(ICGH) in the early sleep stage (n = 24). In addition, the following correlations between GH level with ITT and ICGH in the early sleep stage(n = 20) and between IGF-I(26-46) and an integrated concentration of prolactin (ICPRL) in the early sleep (n = 20) and overnight sleep (n = 7) stages were also examined. IGF-I(26-46) was measured according to the method of Yanaihara with minor modifications. Samples for ICGH were collected every 30 min until 4 hours after sleep by a portable continuous flow blood withdrawal pump(CORMED, MODEL ML6) at a rate of 6 ml/h. Samples for ICPRL from 13 subjects were collected by the same procedure and period as ICGH. On the other hand, samples for ICPRL from 7 subjects were collected during an overnight period. Sleep and wake cycles were almost identical in the subjects tested. Among the subjects tested with ITT and continuous blood sampling for ICGH and ICPRL, patients with pituitary dwarfism were excluded. Serum IGF-I(26-46) levels appeared to be age-dependent, and the highest value was demonstrated in puberty. Some children under 8 years of age showed serum IGF-I(26-46) levels as low as that of pituitary dwarfism. No sexual difference was noticed in IGF-I(26-46) levels. Serum IGF-I(26-46) levels in pituitary dwarfism were apparently low and significantly increased after hGH injection. Serum IGF-I(26-46) levels in patients under 11 years of age with constitutional dwarfism and Turner's syndrome revealed an almost normal result. However, many patients over 11 years of age showed lower levels of serum IGF-I(26-46) than normal subjects, and some cases showed remarkably low levels of serum IGF-I(26-46). Serum IGF-I(26-46) levels in precocious puberty without treatment were slightly high in comparison with age-matched controls.(ABSTRACT TRUNCATED AT 400 WORDS)