Different thresholds of tissue-specific dose-responses to growth hormone in short prepubertal children

BACKGROUND: In addition to stimulating linear growth in children, growth hormone (GH) influences metabolism and body composition. These effects should be considered when individualizing GH treatment as dose-dependent changes in metabolic markers have been reported. Hypothesis: There are different dose-dependent thresholds for metabolic effects in response to GH treatment. METHOD: A randomized, prospective, multicentre trial TRN 98-0198-003 was performed for a 2-year catch-up growth period, with two treatment regimens (a) individualized GH dose including six different dose groups ranging from 17--100 mug/kg/day (n=87) and (b) fixed GH dose of 43 mug/kg/day (n=41). The individualized GH dose group was used for finding dose--response effects, where the effective GH dose (ED 50%) required to achieve 50% Delta effect was calculated with piecewise linear regressions. RESULTS: Different thresholds for the GH dose were found for the metabolic effects. The GH dose to achieve half of a given effect (ED 50%, with 90% confidence interval) was calculated as 33(+/-24.4) mug/kg/day for [increment] left ventricular diastolic diameter (cm), 39(+/-24.5) mug/kg/day for [increment] alkaline phosphatase (mukat/L), 47(+/-43.5) mug/kg/day for [increment] lean soft tissue (SDS), 48(+/-35.7) mug/kg/day for [increment] insulin (mU/L), 51(+/-47.6) mug/kg/day for [increment] height (SDS), and 57(+/-52.7) mug/kg/day for [increment] insulin-like growth factor I (IGF-I) SDS. Even though lipolysis was seen in all subjects, there was no dose--response effect for Delta fat mass (SDS) or Delta leptin ng/ml in the dose range studied. None of the metabolic effects presented here were related to the dose selection procedure in the trial. CONCLUSIONS: Dose-dependent thresholds were observed for different GH effects, with cardiac tissue being the most responsive and level of IGF-I the least responsive. The level of insulin was more responsive than that of IGF-I, with the threshold effect for height in the interval between.