Effect of thyroid hormone therapy on plasma insulin-like growth factor I levels in normal subjects, hypothyroid patients and endemic cretins.
The effect of thyroid hormone therapy (L-T4 or L-T3) on plasma immunoreactive insulin-like growth factor I (somatomedin C, Sm-C) concentrations was studied in 8 normal controls, 14 primary hypothyroid subjects and in 7 patients with endemic cretinism. In normals basal levels of Sm-C (1.56 +/- 0.77 U/ml) increased to (2.46 +/- 1.0 U/ml; L-T4) and to (2.9 +/- 0.95 U/ml; L-T3). Plasma Sm-C basal levels were significantly lower in primary hypothyroid subjects (0.81 +/- 0.48 U/ml) and increased to 2.54 +/- 1.43 U/ml (L-T4) and to 2.16 +/- 0.83 U/ml (L-T3). A significant and positive correlation (r = 0.56) was found between Sm-C and serum T4 and T3 concentrations. Plasma Sm-C concentrations in endemic cretinism were initially normal in 4 patients, but low in the remaining 3 (mean +/- SD: 1.18 +/- 0.63 U/ml) and did not increase after 12 months (1.34 +/- 0.61 U/ml) or 18 months (1.01 +/- 0.43 U/ml) of L-T4 and L-T3 therapy. Plasma T4 levels and free T4 increased considerably in EC after therapy with a significant decrease in the previously elevated plasma TSH concentrations. The subnormal response of plasma Sm-C during effective thyroid thyroid hormone therapy could be an additional factor involved in growth failure of endemic cretins.
D000293:Adolescent; D000328:Adult; D002648:Child; D003409:Congenital Hypothyroidism / Q000097:blood* / Q000188:drug therapy; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000097:blood* / Q000188:drug therapy; D007334:Insulin-Like Growth Factor I / Q000097:blood*; D008297:Male; D013002:Somatomedins / Q000097:blood*; D013963:Thyroid Hormones / Q000627:therapeutic use*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D013002:Somatomedins; D013963:Thyroid Hormones; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I; D013972:Thyrotropin; D013974:Thyroxine