Synthesis of p-Brom-phenylmercapturic Acid by the Fasting Growing Dog

Abstract

The literature on the subject of mercapturic acid synthesis in animals under various dietary regimes has been reviewed by White and Lewis. 1 One group of workers is of the opinion that exogenous cystine sulfur alone determines the synthesis of mercapturic acid, 2 while others maintain that the body tissues are capable of supplying cystine to meet the needs for detoxication of administered brombenzene. 3 McGuinn and Sherwin, 4 contrary to Abderhalden, 3 have demonstrated that acidity or alkalinity of the diet has no effect on the synthesis of phenyl-mercapturic acid in rabbits. By chloroform extraction method, McGuinn and Sherwin 4 were able to isolate mercapturic acid from the urine of rabbits fed brom-benzene while maintained on either acid or alkaline diets.

Thomas 2 was unable to detect mercapturic acid in the urine of fasting dogs. Abderhalden, 3 however, isolated mercapturic acid from fasting dogs' urine, but he believes that the cystine requirements for more essential functions of the body limit the degree of mercapturic acid synthesis.

In all of the above mentioned experiments on fasting dogs, including that of Nishimura's on fasting rabbits, 3 the period of fasting was rather short. The experiments did not exclude the possibility of liberation of cystine from the so-called circulating or stored protein which, as has been shown long ago, 5 is not depleted after short periods of complete fasting. Ashworth and Brody 6 have further shown “that the previous level of dietary protein has a marked influence on the time necessary to reach the endogenous level of nitrogen excretion in the rat.”