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The feasibility of measuring caffeine clearance from saliva (SCl) was assessed in ambulatory patients with liver disease and in a control group, and the results were compared with quantitative liver function tests. For this purpose, the subjects were given 280 mg caffeine p.o. in decaffeinated coffee powder between noon and 4 p.m., and caffeine concentrations were measured in saliva (using an enzyme immunoassay) before bedtime and upon arising. In the cirrhotics (n = 29), SCl was 0.58 +/- S.D. 0.45 ml per min X kg, thus being reduced to approximately one-third of drug-free, nonsmoking controls (1.53 +/- 0.46, n = 18); although patients with noncirrhotic liver disease showed intermediate values (0.95 +/- 0.47), their reduction in SCl was significant (p less than 0.001). SCl was correlated with indocyanine green fractional clearance, galactose elimination capacity and aminopyrine breath test; however, the closest relationship (Rs = 0.80) was observed with the aminopyrine breath test. It is suggested that the measurement of SCl represents a noninvasive and innocuous procedure for quantifying hepatic microsomal function, and is suitable for routine use. Since a.m. saliva concentrations of caffeine are highly correlated (Rs = -0.94) with SCl, further simplification of the test to a single-point measurement appears possible.

The isolated hemoglobin‐free perfused rat liver was used as a model to study the formation of a glutathione S‐conjugate and its disposition into the biliary as well as other extracellular (caval perfusate) compartments. 1‐Chloro‐2,4‐dinitrobenzene was chosen as substrate because it reacts with the glutathione‐S‐transferases at high activity to give rise to an S‐conjugate, S‐(2,4‐di‐nitrophenyl)‐glutathione, a product readily discernible from the parent compound. S‐(2,4‐Dinitrophenyl)‐glutathione formation rates were equal to the infusion rates of 1‐chloro‐2,4‐dinitrobenzene up to 0.3 μmol × min−1× g liver−1. Steady‐state rates of S‐conjugate release were maintained until the glutathione content of the liver had decreased to about 40% of the control value. Biliary excretion of the S‐conjugate was practically quantitative at low rates of S‐conjugate formation, up to about 30 nmol × min−1× g liver−1. and release of S‐conjugate into the caval perfusate gradually increased with the rate of formation. Maximal biliary S‐conjugate concentration was 36 mM. Choleresis associated with biliary S‐conjugate excretion amounted to 18.6 pi of extra bile per μmol of net S‐conjugate excreted. This would correspond to a limiting concentration of 54 mM S‐conjugate in the water compartment associated with biliary transport, e.g. exocytotic vesicle in the context of an exocytosis‐like mechanism of bile formation. The system described here is suited for further investigation of properties of bile formation, as is illustrated by the sensitive detection of changes in the concentration of S‐conjugate in the perfusate upon Ca2+‐depletion.

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