INSULIN-LIKE GROWTH FACTOR AND ITS CARRIER PROTEIN IN HYPOPITUITARY AND HYPOTHYROID CHILDREN AND ADULTS

Utilizing radioligand assays for the somatomedin, insulin-like growth factor (IGF), and its carrier protein (CP), we have compared their serum levels in normal subjects with those in patients with hypopituitarism and hypothyroidism. The mean (±SEM) serum IGF concentration in children (n= 32, 2–13 yr, 929 ± 46 μU/ml) was virtually identical to that in adults (n= 20, 18–50 yr, 916·29 μU/ml), while CP levels in the former (1·8 ± 0·1 mg/ml) were significantly lower (P < 0·01) than in the latter (2·9 ± 0·1 mg/ml). Both serum IGF and CP were significantly decreased (P < 0·001) in hypopituitary children (n= 5, 6–8 yr, 377 ± 52 μU/ml and 0·9 ± 0·1 mg/ml respectively). Likewise, serum IGF and CP were significantly reduced (P < 0·05) in hypothyroid children (n= 10, 1–15 yr, 497 ± 24 μU/ml and 0·8 ± 0·1 mg/ml respectively) and adults (n= 12, 25–55 yr, 723 ± 40 μU/ml and 1·8 ± 0·2 mg/ml respectively). Growth hormone therapy (4 days) significantly increased (P < 0·05) serum IGF in hypopituitary children (336 ± 80 to 559 ± 59 μU/ml) but did not change the CP level (0·7 ± 0·2 to 0·7 ± 0·1 mg/ml). Thyroxine therapy (4–8 months) significantly increased (P < 0·05) both serum IGF and CP levels in hypothyroid children (497 ± 24 to 666 ± 38 μU/ml, and 0·8 ± 0·1 to 1·0 ± 0·1 mg/ml respectively) but had no effect in adults (723 ± 40 to 937 ± 132 μU/ml, and 1·8 ± 0·2 to 2·1 ± 0·2 mg/ml respectively). These studies indicate that growth retardation in children with hypopituitarism and hypothyroidism is associated with significant reductions in serum IGF and CP levels that are corrected, at least in part, by adequate hormone replacement therapy.