DIETARY-PROTEIN SOURCE (SOYBEAN VS CASEIN) AND TAURINE STATUS AFFECT KINETICS OF THE ENTEROHEPATIC CIRCULATION OF TAUROCHOLIC ACID IN CATS

The effect of dietary protein source (soybean vs. casein) and taurine status on kinetics of [24-C-14] and [taurine-2-H-3]taurocholic acid wa s determined by isotope dilution in 10 adult male cats (six taurine-re plete and four taurine-depleted). Taurine-replete cats were fed 1500 m g taurine/kg purified diets containing either 435 g/kg casein (1500 Ca s) or soybean protein (1500 Soy) in a crossover design. Taurine-deplet ed cats were fed the soybean protein diet with no taurine (0 Soy). Spe cific activity of [C-14]- and [H-3]taurocholic acid in bile was determ ined for 6 d following a pulse dose of dual-labeled taurocholic acid. Taurocholic acid pool size was significantly greater in cats when fed the 1500 Soy diet than when fed the 1500 Cas or than in cats fed the 0 Soy diet. Total entry rate, irreversible loss rate and recycling rate of [taurine-2-H-3]taurocholic acid and the irreversible loss rate of [24-C-14]taurocholic acid tended to be greater in cats when fed the 15 00 Soy than the 1500 Cas diet. Irreversible loss rates of taurocholic acid in taurine-replete cats fed the 1500 Soy diet were significantly greater than in taurine-depleted cats, 356 vs. 120-mu-mol/d [24-C-14]t aurocholic acid and 445 vs. 56-mu-mol/d [taurine-2-H-3]taurocholic aci d. The fraction of taurocholic acid was greater, and the fraction of t aurochenodeoxycholic and taurodeoxycholic acids lower in cats when fed the 1500 Soy than when fed the 1500 Cas diet. Taurine-depleted cats h ad less taurocholic, taurochenodeoxycholic, and taurodeoxycholic acids and greater glycocholic and cholic acids than taurine-replete cats fe d the 1500 Soy diet. This study demonstrates that both dietary protein source and taurine status affect taurocholic acid kinetics and bile a cid composition in cats. J. Nutr. 122: 1019-1028, 1992.