Excretion of the glucuronide of thyroxine in cat bile.

1. After intravenous injections of radioactive thyroxine into cats, about half the radioactivity excreted in the bile was in a glucuronide fraction, which, after hydrolysis with beta-glucuronidase, gave rise to radioactive thyroxine and a radioactive substance that ran with 3,3',5'-tri-iodothyronine on paper chromatography in two dimensions. 2. The proportion of the total radioactivity in the bile in the glucuronide fraction was unaffected by an intravenous injection of 750mug. of non-radioactive thyroxine. 3. It is concluded that the capacity of the liver for forming the glucuronides of thyroxine and its metabolites is at least as great in cats as in monkeys. 4. These findings are discussed in relation to the question whether the liver contains one or more than one UDP-glucuronic acid glucuronyltransferase.