Effects of growth hormone on serum lipids and lipoproteins: Possible significance of increased peripheral conversion of thyroxine to triiodothyronine

• Published in: Metabolism, clinical and experimental clinical and experimental, 1996-08, Vol.45 (8), p.1016-1020
• Main Authors: Wolthers, Troels, Lemming, Lone, Grøfte, Thorbjørn, Møller, Niels, Christiansen, Jens Sandahl, Klausen, Ib Christian, Jørgensen, Jens Otto Lunde
• Format: Article
• Language: English
• Subjects: Adult; Biological and medical sciences; Double-Blind Method; Drug Combinations; Growth Hormone - blood; Growth Hormone - pharmacology; Hormones. Endocrine system; Humans; Insulin-Like Growth Factor I - analysis; Lipids - blood; Lipoproteins - blood; Male; Medical sciences; Pharmacology. Drug treatments; Thyroxine - metabolism; Triiodothyronine - biosynthesis; Triiodothyronine - blood; Triiodothyronine - pharmacology
• ISSN: 0026-0495; 1532-8600
• DOI: 10.1016/S0026-0495(96)90273-5

The role of growth hormone (GH) and thyroid hormone in the regulation of lipid and lipoprotein metabolism is not fully established. Furthermore, the possible linkage between the well-known GH-induced increase in peripheral thyroxine (T 4) to triiodothyronine (T 3) generation and the effects of GH on lipid and lipoprotein metabolism has not been elucidated. In this double-blind placebo-controlled study, we compared the effects of GH and T 3 administration alone and in combination on lipid and lipoprotein metabolism in a group of healthy young adults. The dose of T 3 was selected to mimic the T 3 increase seen during exogenous GH exposure. Eight normal male subjects (aged 21 to 27 years; body mass index, 21.11 to 27.17 kg/m 2) were randomly studied during four 10-day treatment periods with (1) daily subcutaneous placebo injections and placebo injections and placebo tablets, (2) daily subcutaneous GH injections (0.1 IU/kg · d) and placebo tablets, (3) daily T 3 administration (40 μg on even dates or 20 μg on uneven dates) plus placebo injections, and (4) daily GH injections plus T 3 administration. GH administration increased free T 3 (FT 3) to the same level as during T 3 administration. GH caused decreased levels of total cholesterol (TC) and low-density lipoprotein (LDL) cholesterol and increased levels of triglycerides (TG) and lipoprotein(a) (Lp(a)), but no changes in high-density lipoprotein (HDL) cholesterol and apolipoprotein B (apo B). T 3 administration caused no alteration in these parameters, except for decreased levels of TC comparable to those seen after GH administration. Combined GH and T 3 administration caused changes identical to those seen after GH administration, in addition to decreased apo B levels and a further decrease of TC levels. We conclude that GH and iodothyronines in the physiologic range exert distinct but disparate effects on lipids and lipoproteins, and do not support the hypothesis that the effects observed during GH administration are exclusively secondary to changes in peripheral T 3 levels.