3-Hydroxy-3-methylglutaryl coenzyme a reductase activity in liver of athymic mice with or without an implanted human carcinoma

Hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase activities and cholest erol content in the liver of athymic mice either bearing or not an implante d human lung mucoepidormoid carcinoma (HLMC) and in the neoplasic tissue, w ere analyzed. The properties of the HMG-CoA reductase of HLMC grown in nude mice and those ones found in the liver of these animals, sacrificed either at mid-light or mid-dark, were similar. The hepatic reductase activity was found to be four- to five-fold greater at mid-dark than at mid-light (462 +/- 141 vs. 123 +/- 22 pmol min(-1) mg protein(-1)). Since the K-m value wa s not modified, the mid-dark activity could be due to an increase in the am ount of enzyme. In contrast, HLMC reductase activity and cholesterol conten t showed similar values at mid-light and mid-dark points. HLMC reductase do es not appear to have any diurnal variation and the cholesterol synthesis a nd content seems to be independent of food intake. HLMC-bearing nude mice u ndergo several alterations in the biosynthesis and homeostasis of cholester ol. Hypocholesterolemia, lower hepatic cholesterol content and higher HMG-C oA reductase activity are characteristic of host mice. (C) 1999 Elsevier Sc ience Inc. All rights reserved.