Quantification of Taurine Synthesis in the Intact Rat and Cat Liver 1

Abstract

Data from studies with liver homogenates indicate livers of different species differ in their ability to synthesize taurine from various substrates. Rat liver synthesizes taurine rapidly from cystine sulfinic acid (CSA) (1, 2), whereas cat and human livers synthesize taurine slowly (1, 2) or not at all (3, 4) from CSA. Recently a system utilizing inorganic sulfate for taurine synthesis has been described and it has been suggested that this pathway may be important in species which lack an active CSA pathway (5,6). No data exist concerning rates or pathways of taurine synthesis in the intact liver of any species. We studied the taurine synthetic capacity of isolated perfused rat and cat livers to quantify total taurine synthesis and to estimate the relative importance of taurine synthesis from CSA and from inorganic sulfate.

Materials and methods. Male Sprague-Dawley rats, 250-350 g, and young cats, 350-500 g, male and female, were used. In perfusions involving [¹⁴C]taurine, 2 μCi of isotope was injected intravenously into the fasted animal 30-60 min before hepatec-tomy. Under ether (rats) or pentobarbital (cats) anesthesia, the inferior vena cava was ligated, cannulas were placed in the superior vena cava, portal vein, and common bile duct, and livers were removed and transferred to a standard perfusion apparatus. 3 In the cat, the cystic duct was ligated. Perfu-sate composition was: Ringer's bicarbonate solution containing 4% bovine serum albumin to which washed bovine erythrocytes were added to a final hematocrit of 33%. 4 Perfusate was gassed with 95% O₂-5% CO₂. Perfusion was by gravity at 1-2 ml/g of liver/min and lasted 300-360 min. Except where noted, sodium cholate was infused into the perfusate at a rate of 0.46 (rat) or 0.91 (cat) μmole/min in order to deplete liver taurine. Livers were biopsied at 1 hr and at the end of perfusion for measurement of hepatic taurine concentration by methods previously described (7).