Effects of halothane anesthesia on equine liver function.

This research investigates the impact of halothane anesthesia on liver function and bile excretion in ponies, finding that the anesthesia causes an increase in the excretion of bilirubin and a decrease in the concentration of bile acids, despite not adversely affecting the activity of conjugation enzymes in the liver.

Objective of the Study

• The main purpose of this research was to study the effects of halothane anesthesia on liver function and biliary excretion in ponies.

Methods Used in the Study

• The study involved the use of ponies that were surgically prepared with chronic external biliary fistulas, also known as T tubes.
• Four studies were performed on two ponies, 2 to 6 months after their surgery.
• The researchers maintained a steady-state bile flow, bilirubin, and bile acid excretion during each study using intravenous bile acid infusion.

Findings from the Study

• The study found that compared to 2-hour preanesthesia values, halothane caused a 138% increase in the excretion of bilirubin from the liver, a 60% increase in biliary bilirubin concentration, and a 43% increase in PCV, a measure of overall blood volume consisting of red blood cells.
• Halothane anesthesia also resulted in a 16% decrease in plasma bilirubin, a 46% reduction in biliary bile acid concentration, and a 27% reduction in bile acid excretion.
• It was observed that the fraction of bile flow that is not dependent on bile acids seemed to increase.
• The study noted that plasma aspartate transaminase concentration, an enzyme indicative of liver injury, did not change during the administration of anesthesia.
• The research also found that there was no significant change in the ratio of conjugated bilirubin fractions in bile during anesthesia and less than 1% was excreted unconjugated.

Interpretation of Findings

• Despite the changes observed, the researchers concluded that halothane anesthesia did not appear to adversely affect the activity of the liver’s transferase-conjugating enzymes, which play a vital role in processing bilirubin and bile acids.
• The study suggests that the greatly increased bilirubin excretion seen during anesthesia may actually be a result of a combination of increased hepatic clearance from the plasma and increased production of bilirubin from the turnover of free hepatic heme or heme from the induced cytochrome P-450 system, a group of enzymes involved in drug metabolism.