Immunoreactive somatomedin B in the human foetus and in women during pregnancy.

Immunoreactive somatomedin B (RIA-B) was identified in foetal organ extracts, amniotic fluid and foetal serum in the second trimester. After separation using a G-200 neutral Sephadex column, the RIA-B activity in the cytosol prepared from foetal organs eluted after the void volume, suggesting the dominance of activity with the molecular weight of approximately 200 K. In contrast, the majority of the RIA-B activity in amniotic fluid eluted around the elution volume, suggesting dominance of activity with a molecular weight of approximately 5 K. Cord blood RIA-B levels were examined and found to be significantly lower than adult levels. A significant correlation between cord blood RIA-B levels, and neonatal weight was found. A longitudinal study during pregnancy showed that RIA-B is increased in both healthy women and in women suffering from hypopituitarism suggesting a pituitary-independent production of RIA-B during pregnancy.