The Effect of Chlorophenoxyisobutyric Acid and Ethinyl Estradiol on Cholesterol Turnover*

Abstract

The fractional turnover rates of cholesterol were measured in 10 subjects with coronary heart disease. C14-cholesterol was complexed with plasma lipoprotelns in vitro and injected intravenously. Isotopic equilibration was reached after 4 weeks, and measurement of the rate of removal of labeled cholesterol was then continued for 2 to 3 months. A significant relationship was found between fractional turnover rate and serum cholesterol concentration. When determinations of initial fractional turnover rates were completed, 6 subjects were treated with chlorophenoxyisobutyric acid and three others with ethinyl estradiol. Both durgs produced falls in plasma cholesterol concentration. The administration of ethyl chlorophenoxyisobutyrate (CPIB) produced a decrease in the rate of fall of cholesterol specific activity indicating a probably inhibition of cholesterol or lipoprotein synthesis. On the other hand, treatment with ethinyl estradiol resulted in an increase in the rate of fall of cholesterol specific activity indicating increased turnover or catabolism.