Regulation of the very low density lipoprotein receptor by thyroid hormone in rat skeletal muscle.

A new member of the low density lipoprotein receptor gene family that binds and internalizes very low density lipoprotein (VLDL) particles was previously cloned and characterized from the rabbit and human. The physiological role of this putative VLDL receptor is not known, but its tissue distribution and ligand specificity suggest a possible role in the delivery of triglycerides to peripheral tissue. To learn more about the potential function of this receptor, we measured the changes in VLDL receptor mRNA and protein in various tissues following dietary or hormonal manipulation of rats. No significant changes in the VLDL receptor mRNA or protein were seen after a 48-h fast and subsequent to refeeding. A striking change in receptor mRNA and protein was observed in skeletal muscle of hypothyroid and hyperthyroid rats. In hypothyroid rats, the amount of immunodetectable VLDL receptor was reduced by 80%, while in the hyperthyroid animals it was increased by 300%. These maneuvers did not affect VLDL receptor mRNA or protein levels in adipose tissue or heart. The changes in VLDL receptor mRNA in muscle were opposite to those observed with lipoprotein lipase. These studies suggest that the VLDL receptor plays a role in a metabolic process in muscle that is regulated by thyroid hormone.