DIFFERENCES IN SERUM INSULIN-LIKE GROWTH FACTOR-I AND SEX-HORMONE-BINDING GLOBULIN LEVELS BETWEEN LATE AND EARLY PREPUBERTY IN PATIENTS WITH IDIOPATHIC AND ORGANIC GROWTH-HORMONE DEFICIENCY

It has been reported that growth hormone modulates serum levels of insulin-like growth factor I (IGF-I) positively and serum levels of sex-hormone-binding globulin (SHBG) negatively. We have measured IGF-I and SHBG concentrations in 24 prepubertal patients with growth hormone deficiency. Twelve of these patients had had intracranial tumors removed (organic growth hormone deficiency) and 12 had growth hormone deficiency of unknown etiology (idiopathic). Fifty-two prepubertal control subjects, admitted for elective surgery, were also studied. All prepubertal patients were divided into two age groups: older and younger than 7 years of age. In both groups there were patients with multiple pituitary deficiencies on hydrocortisone and/or levothyroxine sodium replacement therapy. In the age group younger than 7 years, serum IGF-I was not significantly different between organic and idiopathic growth hormone deficiency (0.28 +/- 0.21 versus 0.062 +/- 0.071 mU/l) but serum SHBG levels were different (74.6 +/- 33.5 versus 173 +/- 59 nmol/l. p < 0.0 5). These values were not significantly different from controls (0.47 +/- 0.25 mU/l and 132 +/- 47 nmol/l, respectively). In the age group older than 7 years, there was no significant difference between organic and idiopathic growth hormone deficiency in serum IGF-I (0.33 +/- 0.17 versus 0.16 +'/- 0.11 mU/l) or serum SHBG (113 +/- 72 versus 108 +/- 17 nmol/l). These values were significantly different from controls (1.04 +/- 0.36 mU/l and 68.7 +/- 31.7 nmol/l, p<0.05. respectively). It is concluded that serum IGF-I and serum SHBG are regulated by growth hormone in late puberty. In early prepuberty, however, the effect of growth hormone on these two serum parameters seems to be weak. This phenomenon could be related to an increase in the sensitivity of the cellular response to the biological effects of growth hormone with age.