Serum bile acid determination for assessment of hepatic injury in the woodchuck.

A direct spectrophotometric assay for determination of the serum bile acid concentration in the woodchuck (Marmota monax) has been validated. The assay relies on the conversion of 3-hydroxy bile acids to 3-oxo bile acids by 3 alpha-hydroxysteroid dehydrogenase with concomitant reduction of NAD+ to NADH. Reduction of NAD+ is coupled via a diaphorase catalyst to the formation of a diformazan dye from nitrotetrazolium blue and the diformazan product is measured spectrophotometrically at 540 nm. Interfering endogenous dehydrogenase activity present in woodchuck sera was inactivated with sodium pyruvate. Mean recovery of seven exogenous bile acids added to woodchuck sera was 102.0 +/- 2.2%. Intra-assay precision was determined with ten replicate samples giving a mean +/- standard error of the mean of 1.94 +/- 0.12 micron/L with a coefficient of variation of 3.9%. The mean serum bile acid concentration determined in 33 clinically healthy animals was 5.52 +/- 0.81 micron/L. The serum bile acid concentration increased following surgical ligation of the bile duct from 3.78 +/- 0.58 micron/L to a maximum value of 148.0 +/- 30.7 micron/L and remained increased for the 42 day study period. In woodchucks treated with carbon tetrachloride, the serum bile acid concentration peaked at 16 hours following treatment at 72.7 +/- 29.3 micron/L, and returned to pretreatment concentration within 6 days. The serum bile acid concentration therefore appears to be a sensitive biochemical test of cholestasis and hepatocellular forms of hepatic injury and of potential value in the clinical assessment of hepatic disease associated with woodchuck hepatitis virus infection.