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.
Correlation was observed between neither IGF-I (26-46) and basal GH nor between IGF-I (26-46) and GH response (both maximum GH level and maximum GH increase from basal level) in ITT. Additionally, no correlation was observed between GH response in ITT and ICGH in the early sleep stage. However, a statistically significant positive correlation was observed between IGF-I (26-46) and ICGH (both maximum and mean ICGH) in the early sleep stage. No correlation was noticed between IGF-I (26-46) and ICPRL (both maximum and mean ICPRL) in either the early or overnight sleep stages.
These results suggest the following :
1) When interpreting the absolute value of IGF-I (26-46), subject age should be considered because IGF-I (26-46) value changes with age. 2) Some etiological factors such as short stature seen in Turner's syndrome or constitutional dwarfism may be due to defective IGF-I. Overgrowth in precocious puberty may be due to increased IGF-I in addition to increased sex hormones. 3) Continuous stimulation of GH is important to generate IGF-I. Hence basal GH level and GH response in the provocative test do not always reflect the physiological GH action of generating IGF-I. 4) Prolactin does not play an important role generating IGF-I in the status of normal GH secretion. 5) IGF-I (26-46) is thought to be a good indicator for IGF-I.
