Effect of growth hormone on adipose tissue and skeletal muscle lipoprotein lipase activity in humans.

Lipoprotein lipase (LPL) is involved in clearing triglyceride-rich chylomicrons and very-low-density lipoprotein particles from the bloodstream, providing free fatty acids to particular adipose tissue for storage and to skeletal muscle tissue for oxidation and energy production. Although the same gene (chromosome 8p22) encodes LPL, the enzyme activity is regulated in a tissue-specific manner. Dysfunction of the LPL enzyme has been implicated in the pathogenesis of dyslipidemia (high triglyceride and low high-density lipoprotein (HDL) cholesterol), early arteriosclerosis, and the pathogenesis of obesity. Treatment with growth hormone (GH) both in vivo and in vitro results in a pronounced reduction (often up to 50%) of LPL activity in adipose tissue in humans. The specific level of messenger ribonucleic acid, however, is not generally affected by GH treatment in adipose tissue, indicating that the effect of GH is mediated at a post-translational level. The GH-mediated reduction in adipose tissue LPL activity may be involved in the reduction in adipose tissue mass commonly seen after prolonged GH treatment in GH-deficient adults and GH treatment in obese subjects. LPL activity in adipose and skeletal muscle tissue is generally regulated in a reciprocal manner by, for example, fasting, feeding, insulin and epinephrine. A high level of LPL activity, particularly in skeletal muscle tissue, has been found to be associated with a beneficial lipoprotein profile (low triglyceride and high HDL cholesterol). In investigations where obese but otherwise healthy women were treated with GH, and in another study where adults with GH deficiency were treated for 4 months with GH, we found no effects of GH on either skeletal muscle LPL activity nor on skeletal muscle LPL gene expression. In conclusion, GH has a pronounced inhibitory effect on adipose tissue LPL activity, which is mediated at a post-translational level. The GH-induced reduction in adipose tissue mass may be partly mediated by this effect on adipose tissue LPL. GH has no effects on LPL activity in skeletal muscle, which may be related to the fact that GH has no or only minor effects on plasma triglyceride and HDL cholesterol levels. Finally, GH is not, unlike for example insulin and catecholamines, involved in antagonistic regulation of LPL in muscle and adipose tissue.