Dietary Sulfate and the Excretion of Glycocholic and Taurocholic Acids in the Rat

The relationship of dietary sulfate and the availability of taurine in the tissues to the relative conjugation of cholic acid with glycine and taurine to form the bile acids, glycocholic and taurocholic acids, in rats was investigated by feeding diets which contained different levels of total sulfur as sulfate and different neutral to inorganic sulfur ratios. Following stomach-tube feeding of cholic acid-24-¹⁴C, the relative conjugation, glycocholic:taurocholic ratio (G:T ratio), was determined by extracting the bile acids from the intestinal contents of the jejunum-ileum section of the small intestine. The bile salts were separated by thin-layer chromatography and visualized by an ethanolic phosphomolybdic spray. The appropriate spots were removed from the plates and the radioactivity of the samples evaluated by liquid scintillation.

The G:T ratio of animals fed the "normal" diet which contained 0.10 percent inorganic sulfur and 0.57 percent organic sulfur was the smallest indicating the highest relative conjugation with taurine. Increased taurine conjugation in relation to glycine conjugation has been associated with low serum cholesterol levels and limited atherosclerosis. The diet containing a high inorganic sulfur level (0.42 percent) and no added cysteine had the largest G:T ratio corresponding to the smallest relative amount of taurocholic acid. Likewise, in the diets which contained low levels of inorganic sulfur, the G:T ratios were larger than that of the "normal" diet. These data have been interpreted to indicate that either too high or too low a level of inorganic sulfur causes changes in the relative conjugation of taurine. Requirements other than taurine availability which affect bile acid conjugation were also considered in relation to the present findings. The results of this study have been interpreted to imply that the level of inorganic sulfur in the diet may serve an important regulatory function in bile acid conjugation.