Metabolism of ursodeoxycholic acid in the Japanese flounder (Paralichthys olivaceus) and the yellowtail (Seriola quinqueradiata)

The tissue uptake and turnover of ursodeoxycholic acid (UDCA) in the Japane se flounder (Paralichthys olivaceus) and the yellowtail (Seriola quinquerad iata) were investigated by using [C-14-24] UDCA to gain understanding of UD CA metabolism in fish. In the experiment with flounder, a diet containing [ C-14]-UDCA was orally administrated to the fish (total length, 13.0 cm body weight, 18.7 g). Twenty-four flounder were held in a tank at 24 degrees C for 0.5, 1, 3, 6, 9, 12, 24, and 48 h, at which time the stomach, pyloric c aeca, liver, kidney, gall bladder, and intestines from three fish for each sampling time were dissected for radioactive measurements. Bile acids were extracted from the above tissue samples after hydrolysis. A similar experim ent was conducted using 20 young yellowtail (total length, 16.5 cm body wei ght, 44.0 g). In the flounder, orally administrated [C-14]-UDCA was absorbe d effectively (% absorption = more than 95%), and mainly transported to the gall bladder. The biological half-lives of UDCA in the gall bladder, intes tine, and whole body of the flounder were 139.1, 3.6, and 67.9 h, respectiv ely. In the flounder, UDCA was excreted mainly in the feces. The tissue upt ake of dietary UDCA in yellowtail was similar to that observed in Japanese flounder. These results suggested that UDCA was circulated between the live r and intestine via the gall bladder and scarcely distributed in other tiss ues and organs in either the flounder or the yellowtail. However, the biolo gical half lives of UDCA in the gall bladder (26.6 h) and whole body (6.2 h ) of yellowtail were shorter than those in Japanese flounder. This indicate s a more rapid turnover of UDCA in the yellowtail than in the flounder. (C) 1999 Elsevier Science B.V. All rights reserved.