Sulfur metabolism. III.

Abstract

The addition of cystine, cysteine or their derivatives to the control rations of rabbits caused a prompt and marked increase in the amount of sulfur eliminated in the urine. When these sulfur compounds were withdrawn the elimination of sulfur dropped to the control level, and in some instances even below this. This decrease in sulfur took place in the first two days of the period following the cystine sulfur feeding, and in most cases the first day. On the day following this marked depression of the sulfur elimination there was a distinct increase of sulfur in the urine. The cystine sulfur was not completely eliminated in the period during which it was fed, except in cases of phenyl acetyl benzyl cysteine. The increased sulfur output following the depression of sulfur elimination is considered as a lag. It would seem that the R-SH type of sulfur compound has some specific effect upon the mechanism of sulfur excretion. This effect is observed both with reduced sulfur and oxidized sulfur, but not with conjugated SO₄. In three cases, however, there was an increase in conjugated SO₄—namely 6 mg. for phenyl acetyl benzyl cystine and phenyl hydantoin cystine, and 10 mg. for acetyl benzyl cysteine. This “deferred lag” was unforeseen and must be taken into special account in our next series of this program. The excess elimination of sulfur in some of the tests may be charged to thils “deferred lag”-but not altogether. In the case of phenyl acetyl benzyl cysteine the increased sulfur elimination exceeded the cystine sulfur added to the ration by one-half its amount. This could not come from any previously ingested R-SH added to the animal's normal ration. There seems to be positive evidence that ingestion of R-SH causes a sulfur elimination in addition to the sulfur immediately taken in so that the per cent of cystine sulfur as given in the table may include some endogenous reduced sulfur.