Acute and chronic somatomedin-C response to growth hormone: evaluation of correlation with age and growth rate

Abstract

The correlation between acute and chronic SM-C responses to hGH treatment of hypopituitary dwarfism, and their value in predicting growth rates were studied in 20 GH-deficient children. SM-C by RIA and RRA was measured prior to hGH, 12 hours after 4 daily injections of hGH, 0.1 U/kg, and after 6 months of hGH 0.1 U/kg t.i.w. The correlation between SM-C by RRA and RIA was highly significant (r=0.92 on Day 1 and at 6 months, p <0.001). The acute SM-C response to hGH was predictive of chronic SM-C levels (Day 5 vs. 6 month SM-C, r=0.80, p <0.001). However, individual SM-C responses were variable, with 7 children achieving SM-C levels >1 U/ml by Day 5, while 3 maintained levels <0.10 U/ml. Although the annual growth rate increased from 3.6 ± 0.1 to 6.7 ± 0.6 cm/yr, no correlation was observed between growth rate and baseline, acute or chronic SM-C levels. Children under 10 years of age had the smallest increment in SM-C, but the best growth rate. However, even when subdivided by age, no correlation was observed between 6 month SM-C and growth rates (r=0.10, p >0.75). We conclude that (1) the acute SM-C response to hGH predicts chronic SM-C levels, (2) SM-C and growth response to hGH are age-dependent and (3) the level of SM-C elevation with hGH cannot predict growth response.