ASSESSMENT OF GROWTH-HORMONE (GH) AXIS IN TURNERS SYNDROME USING 24-HOUR INTEGRATED CONCENTRATIONS OF GH, INSULIN-LIKE GROWTH FACTOR-I, PLASMA GH-BINDING ACTIVITY, GH BINDING TO IM9 CELLS, AND GH RESPONSE TO PHARMACOLOGICAL STIMULATION

The GH axis was studied in Turner's syndrome (TS) patients. Thirty-seven prepubertal TS patients and 42 normally growing girls (NGG; 5.5-16.3 yr old), of whom 13 were prepubertal, were studied by 24-h continuous blood withdrawal and provocative tests. The 24-h integrated concentrations of GH (IC-GH), FSH (IC-FSH), and insulin-like growth factor-I (IC-IGF-I) as well as the IC-IGF-I/IC-GH ratio were determined. An increase in IC-GH with age and progression of puberty was found in NGG, but not in TS. IC-GH in the NGG was significantly higher than that in age-matched TS patients. Estrogen replacement therapy normalized IC-GH levels in 6 TS patients in whom these levels were subnormal for age. A positive correlation between IC-GH and IC-FSH or IC-estradiol was found in NGG (r = 0.462; P < 0.01), but not in TS patients. The IC-IGF-I/IC-GH ratio was significantly higher in the TS than in the NGG group. Serum GH-binding activity and serum GH binding to IM9 cells in the TS group did not differ from those in the normal group. We hypothesize that the growth retardation of TS results from a combination of insufficient GH secretion, mainly due to sex steroid deficiency, and an end-organ resistance to IGF-1. IGF-I receptor studies are needed to test this speculation about IGF-I resistence.