Direct spectrometric determination of serum bile acids in the dog and cat.

Serum bile acid concentrations have been shown to be a predictive indicator of hepatobiliary disease in persons. However, there has been only limited use of bile acid values in the clinical diagnosis of hepatobiliary disease in the dog and cat because of technical difficulties associated with many bile acid assays. A rapid enzymatic method previously developed for the quantitation of 3-hydroxy bile acids in persons has been adapted for use in the dog and cat. Nonsulfated 3-hydroxy bile acids are converted to 3-oxo bile acids by 3 alpha-hydroxysteroid dehydrogenase and reduction of NAD+ to NADH. In a coupled diaphorase catalyzed reaction, H+ is transferred to nitrotetrazolium blue to produce a diformazan dye, which is measured spectrophotometrically at 540 nm. Nonspecific interfering dehydrogenase activities present in the dog and the cat serums were inhibited by heating the serum to 60 C for 30 minutes or by the addition of sodium pyruvate. Standard curves prepared from various serum sodium taurocholate concentrations in dogs and cats are linear to 250 mumol/L. The assay is sensitive for the detection of bile acid concentrations as low as 2.5 mumol/L in sera from dogs and cats. In validation studies quantitative recovery of known concentrations of 7 primary and secondary, conjugated and unconjugated, 3-hydroxy bile acids from pooled canine serum was 95.3 +/- 7.9% (mean +/- SEM) and that from pooled feline serum was 101.4 +/- 8.2%.(ABSTRACT TRUNCATED AT 250 WORDS)