Validation of an automated technique for the measurement of glutathione S-transferase in plasma of sheep

Standard tests for liver damage testing in sheep include glutamate dehydrogenase, aminotransferases and lactate dehydrogenase. The first is a mitochondrial enzyme which is fairly liver specific, while the others lack organ specificity, Glutathione S-transferase (GST, EC 2.5.1.18) is a cytosolic enzyme which has a high activity in hepatocytes and is thus a candidate enzyme marker of liver damage. An automated procedure based on the conjugation of 1-chloro-2,4-dinitrobenze ne was adapted on a centrifugal analyser and validated for sheep plasma. The limit of quantification was about 0.5 U l(-1) and the coefficient of variation of between-series reproducibility was less than 4%. Reference values did not differ according to breed, sex or age(n = 139; nine males, 100 females, 30 undetermined; 127 Lacaune and 12 Manech sheep; 41 animals 3-9 months of age, 98 animals 2-6 years of age). The distribution was log-normal and the median and geometric means were 5.1 U l(-1) and 10.0 U l(-1), respectively. The 0.025 and 0.975 quantiles were 2.3 U l(-1) and 18.4 U l(-1). Plasma GST showed a circadian rhythm with a minimum (about 60% of maximum) from 17:00 to 05:00 h and was not significantly altered by repeated daily fine needle liver biopsies for 5 days. In experimental liver damage by intraruminal administration of 0.20 mi kg(-1) BW CCl4, plasma GST was increased 90-fold in the 24th hour, then returned to baseline by day 4. Thus, plasma GST could be an interesting candidate marker for liver damage testing in sheep.