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

Abstract

The tissue uptake and turnover of ursodeoxycholic acid (UDCA) in the Japanese flounder ( Paralichthys olivaceus) and the yellowtail ( Seriola quinqueradiata) were investigated by using [ 14 C -24] UDCA to gain understanding of UDCA metabolism in fish. In the experiment with flounder, a diet containing [ 14 C ]-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°C for 0.5, 1, 3, 6, 9, 12, 24, and 48 h, at which time the stomach, pyloric caeca, 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 experiment was conducted using 20 young yellowtail (total length, 16.5 cm body weight, 44.0 g). In the flounder, orally administrated [ 14 C ]-UDCA was absorbed effectively (% absorption=more than 95%), and mainly transported to the gall bladder. The biological half-lives of UDCA in the gall bladder, intestine, and whole body of the flounder were 139.1, 3.6, and 67.9 h, respectively. In the flounder, UDCA was excreted mainly in the feces. The tissue uptake of dietary UDCA in yellowtail was similar to that observed in Japanese flounder. These results suggested that UDCA was circulated between the liver and intestine via the gall bladder and scarcely distributed in other tissues and organs in either the flounder or the yellowtail. However, the biological 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 indicates a more rapid turnover of UDCA in the yellowtail than in the flounder.