Synthesis of taurine in rat liver and brain in vivo

The in vivo formation of taurine and the analysis of labeled taurine precursors was examined in rat brain and liver at different times after an intracisternal injection of [35S]cysteine and an intraperitoneal injection of [3H]cysteine, simultaneously administered. The distribution pattern of radioactivity was similar in liver and brain. Most of the labeling in both organs (85% in brain and 80% in liver) was recovered in glutathione (oxidized and reduced), cysteic acid, cysteine sulfinic acid, hypotaurine, cystathionine, and a mixed disulfide of cysteine and glutathione. The relative rates of labeling of cysteine sulfinic acid and taurine in liver and brain suggest than in vivo, liver possesses a higher capacity for taurine synthesis than brain. A small amount of [3H]taurine was detected in brain after intraperitoneal injection of [3H]cysteine. The time of appearance of this [3H]taurine as well as the fact that it occurs when [3H]cysteine is not detectable in brain or plasma suggests that it was probably not synthesized in brain from labeled precursors but formed elsewhere and transported into the brain through an exchange process.