Further Studies of the Metabolism of Taurine-s35 by the Rat*

In a recent study (1) of the metabolism of taurine-S35 and taurocholate-S35 in the rat, a significant tissue retention of labeled sulfur. was observed 24 hours after the administration of taurine-S36. This tissue retention was increased and the urinary excretion decreased by preparatory feeding of a diet low in organic sulfur. Machlin et al. (2) have observed that 65 per cent of injected sulfate-S35 was incorporated into the tissues of 1 day-old chicks as taurine sulfur. Lowe and Roberts (3) have described the incorporation of sulfate sulfur into the tissue of chick embryos, and this was largely accounted for in the free taurine of tissue. These observations are not entirely consistent with the classical description of taurine as a biologically inactive end-product of cystine metabolism (4). The present study was undertaken as a part of continued interest in the mechanisms involved in the hypercholesterolemia associated with the feeding of diets high in cholesterol and low in organic sulfur (5, 6). The original findings of the effect of diet on the excretion of trace doses of taurine-S35 have been expanded and the chemical pathways of S36 fixed in the tissue clarified. In this study, it was observed in normal rats that the levels of intake of taurine influenced the urinary excretion of injected taurine-S35. The feeding of diets low in protein resulted in reduced urinary excretion of taurineS35, while the addition of cystine or cysteic acid resulted in an increased excretion of S35. The feeding of cholesterol or the injection of bromobenxene was shown to decrease the urinary excretion of taurine-S35. The Sa5 in the tissue of the animals was shown to be largely absent from the material precipitable with trichloroacetic acid and to be completely absent from