Effect of thyroxine and growth hormone on the hypercholesterolemia of growth hormone deficiency

To study the selective effect of thyroid hormone and growth hormone, alone and in combination on plasma cholesterol, 12 children were monitored monthly during three 4-month treatment periods. Plasma cholesterol was unaltered by growth hormone therapy alone (mean +/- SD, basal cholesterol level: 202 +/- 26 mg/dL; cholesterol level after growth hormone 200 +/- 24 mg/dL). With thyroxine (T4) replacement alone, or combined with growth hormone, a significant (P less than 0.01) decrement in plasma cholesterol occurred. (Thyroxine alone: 172 +/- 11 mg/dL; thyroxine and growth hormone: 172 +/- 10 mg/dL). Basal thyroid function tests, including TRH stimulation, were normal. Serum thyroxine levels decreased and serum triiodothyronine (T3) levels increased in response to growth hormone therapy. Linear growth increased significantly in response to growth hormone alone and both therapies combined. Serum values of T4 and T3 were significantly (P less than 0.001) correlated with basal cholesterol, r = 0.84 and r = 0.83, respectively. Our experience with euthyroid growth hormone deficiency confirms that modest hypercholesterolemia is characteristic of that disorder, and that growth hormone therapy has no statistically significant effect on plasma cholesterol. The modest hypercholesterolemia that does respond to thyroid replacement is further evidence of a subtle abnormality of thyroid function in such individuals. The mechanism whereby thyroid hormone has its cholesterol lowering effect in these apparently euthyroid subjects is unclear.