Effects of the Selective α1-Antagonist, Doxazosin, on Hepatic Lipid Levels and Metabolism in the Golden Hamster

Abstract

The effect of the selective alpha 1-antagonist, doxazosin, on lipid metabolism was studied in cholesterol-fed golden hamsters. The hamsters were studied after short-term (1 week) and long-term (6-8 weeks) treatment. Doxazosin was added to the food (0.05-0.1%). Doxazosin lowered, within 1 week, plasma cholesterol and triglyceride concentrations by 12 and 19%, respectively. These effects were slightly larger during long-term treatment (cholesterol by 15% and triglycerides by 27%). Lipoprotein lipase (LPL) activity in postheparin plasma or in adipose tissue or heart was affected by doxazosin. The hepatic triglyceride secretion rate was lowered by 40%. Doxazosin treatment partially prevented the accumulation of cholesterol and triglycerides in the liver. Hepatic cholesterol synthesis was decreased by 25-40%. When determined under optimal conditions, i.e., after prior dephosphorylation, the hepatic microsomal HMG-CoA reductase activity was lowered by 10-25% in the doxazosin-treated animals. However, if HMG-CoA reductase was determined under conditions to prevent phosphorylation and dephosphorylation of the enzyme, representing the in situ expressed activity, the activity in the doxazosin-treated animals was 40% lower than in the controls. These results indicate that the plasma lipid-lowering effect of doxazosin is largely due to its interference with hepatic lipid metabolism and that one of the effects is a lowering of hepatic cholesterol synthesis, probably due to an increase in the phosphorylation grade of HMG-CoA reductase.