SOMATOMEDIN AND GROWTH HORMONE IN THE NEWBORN

Abstract

Somatomedin (SM) was measured by porcine cartilage bioassay and growth hormone (GH) by radioimmunoassay in 52 full term cord plasmas and 28 maternal plasmas. The SM in cord plasma ranged from 0.22 U/ml to 0.94 U/ml with a mean of 0.50 ± 0.19 U/ml (m ± S.D.) compared to an adult standard plasma pool of 1.0 U/ml. This was not statistically different from the SM of the maternal samples, 0.41 ± 0.20 U/ml with a range of 0.19 U/ml to 1.00 U/ml. The cord GH levels of 41.7 ± 36 mμg/ml were significantly higher than the maternal GH levels, 8.3 ± 4.7 mμg/ml, p≤0.01.The low relative value of SM in the cord plasma is consistent with that found during early childhood, and may reflect a physiologically lower level of requirement. The high neonatal GH levels are hypothesized to be a compensatory increase to overcome factors suppressing SM production. Estrogens are known to be one factor preventing the stimulation of SM by GH. Estradiol (E2) was measured by competitive protein binding in 20 cord plasmas and was markedly elevated in all, ranging from 1.05 to > 5 mμg/ml. In addition, it is possible that the production mechanism for SM is not fully mature in fetal life. These observations are consistent with the hypothesis that SM is involved in the feedback control of GH and that the high newborn GH levels reflect the competence of this mechanism, not immaturity.

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