The metabolism of S-carboxyalkylcysteines in man

1. The ingestion of S-(2-carboxy-1-methylethyl)-, S-(2- carboxy-1-methylpropyl)-, S-(1-carboxy-2methylpropyl)- and S-(2-carboxyethyl)-L-cysteine by man was followed by the excretion in the urine of the unchanged amino acid and the N-acetylated compounds. 2. In the rat the fraction of S-(2-carboxy-1-methylethyl)-L-[U-14C]cysteine acetylated increased as the dose level decreased. 3. The significance of these results for the excretion of S-carboxyalkyl-cysteines in man is discussed.

Dependence upon bile volume of the biliary excretion of bromocresol green and amaranth in the anaesthetized rat

The kinetics of the biliary excretion of both bromocresol green and amaranth are better described in terms of rate equations that are functions of the cumulative volume of bile excreted rather than of time. The rate of disappearance of bromocresol green from the liver also appears to depend on the volume of bile excreted rather than on time. It is proposed that bromocresol green, and probably also amaranth, rapidly equilibrates between the hepatic and biliary compartments as a result of reabsorption from the biliary tree and that the rate-limiting factor in the biliary excretion of these dyes is the removal of dye from the biliary tree by bulk flow. Six methods for the graphical presentation of excretion data are examined and their use in the characterization of the kinetics of an excretion system is discussed.