Effects of d- and l-triiodothyronine and of propylthiouracil on the production of bile acids in the rat

Abstract

The influence of d - and l -triiodothyronine (DT3 and LT3) and propylthiouracil (PTU) on turnover rate and pool size of bile acids in rats on a normal diet has been investigated. No significant difference was observed between half-lives of bile acids in normal, thyroid hormone-treated, or PTU-treated rats. All thyroid hormone-treated rats, however, had a chenodeoxycholic acid (CDC) pool that was 2–3 times greater (means ranging between 6.9 and 10.2 mg) than that of normal rats (mean 3.2 mg). The mean size of the cholic acid (C) pool in DT3-treated (13.5 mg) and LT3-treated (16.6 and 13.5 mg) rats was similar to that of normal rats (12.5 mg), which means that the total bile acid pool (C + CDC) tended to be increased. The size of the total bile acid pool in the PTU-treated rats (mean 16.3 mg) was very similar to that of untreated rats (mean 15.7 mg). When daily production of bile acids (C + CDC) was calculated from the values of turnover rate and pool size, it was found that normal rats had an average synthesis of 4.9 mg bile acids per day, while the production for the LT3- and DT3-treated rats averaged about 8.0 mg/day. This tendency towards increased total bile acid production in the thyroid hormone-treated rats was mainly due to a 2- to 3-fold increase in the daily synthesis of CDC. The PTU-treated rats, on the other hand, had a mean daily bile acid synthesis of 4.7 mg, which is very similar to that found in normal rats.