The Relation between Growth Velocity and Serum Somatomedin C Concentration*

Abstract

The relation between serum somatomedin C (SmC) concentration and growth velocity [gain in height (ΔH)] was investigated in five normal children, four GH-deficient (GHD) children, and five girls with Turner syndrome (TS), three of whom had the karyotype 45Χ and two of whom had the karyotype 46, Xi(Xq). At the beginning of the 12-to 20-month study, all subjects were 8-10 yr old. The normal children received no treatment. After a 6-month control period, the GHD group received 0.04 U human GH (hGH)/kg-day for 6 months, then 0.08 U hGH/kg-day for 6 months. The group with TS received during successive 4-month periods: no treatment, oxandrolone (0.125 mg/kg-day), hGH (0.08 U/kg-day), and oxandrolone plus hGH. Serum SmC and height were measured monthly in all subjects. In the normal children, SmC fluctuated between 0.47-3.10 U/ml, with an average of 1.32, and AH varied between 0.0-1.2 cm/ month, with an average of 0.42. SmC and AH were significantly correlated in all children (0.62 < r < 0.92), and were related by the average equation: ΔH = –0.32 + (0.58) (SmC). In GHD children, the mean baseline SmC level was only 0.13 U/ml, and the mean AH only 0.06 cm/month. hGH (0.04 U/kgday) raised these values to 0.46 U////ml and 0.39 cm/month, respectively, and 0.08 U hGH/kg-day caused further increases to 0.88 U/ml and 0.95 cm/month. AH and SmC in GHD children were related by the average equation: AH = –0.09 + (1.27) (SmC). In TS, the average baseline SmC level was normal (0.92 U/ ml), but AH was depressed (0.09 cm/month). Oxandrolone raised these values to 1.29 U/ml and 0.14 cm/month. hGH (0.08 U/kgday) raised SmC to 1.84 U/ml and AH to 0.19 cm/month. Oxandrolone plus hGH had a supraadditive effect on both SmC, which rose to 3.45 U/ml, and on AH, which accelerated to 0.51 cm/month. AH was related to SmC in TS by the average equation: ΔH = –0.11 + (0.18) (SmC). The regression slope of ΔH vs. SmC was significantly greater than normal in GH deficiency and was significantly less than normal in TS, findings which suggest peripheral hyperresponsiveness to SmC in GH deficiency and hyporesponsiveness in TS.