Bile acid metabolism in hypothyroid subjects: response to substitution therapy

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Abstract
Bile acid kinetics and biliary lipid composition were determined in 10 hypothyroid patients before and after treatment with L-thyroxine. Hypothyroid patients had normal synthesis rates of cholic acid and chenodeoxycholic acid. Hormone treatment, which lowered plasma cholesterol by .apprx. 35%, stimulated the formation of chenodeoxycholic acid by .apprx. 40% but did not significantly change the synthesis of cholic acid or total primary bile acids. The mean relative biliary concentration of deoxycholic acid was decreased from 30 to 19%, and that of chenodeoxycholic acid was concomitantly increased. Cholesterol saturation of bile was decreased by treatment in 6 of the patients, but the mean value before treatment (135 .+-. 13%) was not significantly different from that obtained after treatment (108 .+-. 9%). The hypocholesterolemic effect of thyroid hormones may not be primarily due to an increased degradation of cholesterol to bile acids. Similar to what is observed in heterozygous familial hypercholesterolemia, the defective receptor-mediated degradation of plasma low density lipoproteins in hypothyroidism is thus apparently associated with a quantitatively normal catabolic rate of cholesterol to bile acids.

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