Effects of gonadotrophin-induced elevation of serum testosterone upon somatomedin C levels and serum thymidine activity in children.

3H-thymidine uptake into lectin-activated human lymphocytes allows to measure a growth-stimulating activity of serum, the thymidine activity (TA), which is GH dependent in vivo and related to somatomedins (Sm). In this work, it is shown: that addition of human chorionic gonadotrophin (HCG) or testosterone in vitro does not increase the 3H-thymidine uptake into lymphocytes; that the gonadotrophin-induced elevation of testosterone in children is accompanied by a significant increase of TA and, at a lesser degree, of Sm C; that these two increases are significantly correlated, and that the age-related variation of TA and Sm C after HCG stimulation test are not parallel.