One hundred and fifty-five children with insulin-dependent diabetes mellitus were studied to determine the relationship of plasma somatomedin C concentrations to pubertal stage, recent blood glucose control, duration of diabetes, and daily insulin dosage. Plasma somatomedin C, as measured by radioimmunoassay, increased with age and the progression of puberty in both boys and girls, but was not different from those of normal children aged 5–18 yr. In diabetic children under 5 yr of age, plasma somatomedin was significantly lower than in normal children. These results are different from those reported previously in diabetic children, in which somatomedin activity was measured using a pig cartilage bioassay.
In boys, puberty was accompanied by an increase in hemoglobin A1c from 11.6 to 14.1% despite a 36–44% increase in total daily insulin dosage adjusted for body weight. In girls, puberty was also associated with an increase in hemoglobin A1c (12.1–15.1%) without a change in weight-adjusted insulin dose. Although there was no apparent correlation between hemoglobin A1c and somatomedin C in the group as a whole (r = −0.078), multiple regression analyses demonstrated a significant negative correlation between these two variables (P < 0.001) when considered independently of age, sex, pubertal stage, duration of diabetes, and insulin dose. Pubertal status had a significant (P < 0.01) effect on plasma somatomedin C; plasma somatomedin C was also significantly positively correlated with the duration of diabetes (P < 0.01) but not with weight adjusted insulin dose. SMC concentration was not correlated with age when this variable was considered independently of puberty (P = 0.26). The data indicate that puberty and metabolic control both have significant yet independent effects on somatomedin C in children with insulin-dependent diabetes. In addition, the increased somatomedin C associated with puberty may contribute to the accelerated development of diabetic complications seen at this time, while the lowering of somatomedin C associated with worsening metabolic control may adversely affect linear growth.