EXCRETION OF TAURINE AND SULFATE IN RATS FED WITH A LOW-PROTEIN DIET

The effects of a low protein diet on the excretion of sulfate and taur ine, major metabolites of L-cysteine in mammals, were studied in rats fed with synthetic 10% (group A) and 25% (group B) casein diets. The a verage excretions of total taurine (taurine plus hypotaurine) and tota l sulfate (free plus ester sulfate) (mu mol/kg of body weight per day after the adaptation to the synthetic diet) in group A were 14.2 +/- 1 3.4 and 122.3 +/- 39.6, respectively, which were very low compared wit h 280.4 +/- 93.8 and 943.2 +/- 144.8, respectively, in group B. The ta urine/sulfate ratio in group A was 0.12 +/- 0.11, which was significan tly lower than that (0.30 +/- 0.08) in group B. A single intraperitone al injection of 5 mmol of L-cysteine per kg of body weight in group A resulted in an increase in average taurine and sulfate excretion to 69 3.4 +/- 195.6 and 2440.6 +/- 270.0, respectively, and thus the average taurine/sulfate ratio increased to 0.29. These increases were transie nt and low taurine excretion resumed again 24h after the L-cysteine ad ministration. L-Cysteine injection in group B resulted in a similar in crease in taurine and sulfate excretion, but the ratio changed only sl ightly (0.28). The present results suggest that in vivo production of taurine is reduced preferentially over sulfate production when sulfur amino acid supply is limited.