Hepatobiliary transport of indocyanine green and sulfobromophthalein in fed and fasted horses.

The research investigates the effects of fasting on the hepatic transport of two organic anions, sulfobromophthalein (BSP) and indocyanine green (ICG), in horses. Results indicate that a 3-day fast leads to a significant decrease in the plasma clearance of both anions, suggesting a generalized decrease in hepatic conjugating capacity during fasting.

Hypothesis and Study Design

• The study is based on the hypothesis that fasting can lead to a general decrease in the liver’s ability to conjugate, resulting in reduced plasma clearance of BSP and ICG.
• To test this hypothesis, the researchers subjected 10 healthy horses and 2 ponies to a 3-day fast. The mL/min/kg clearance of BSP and ICG was then observed in these samples.
• The ponies had diverted enterohepatic circulations due to the presence of indwelling T tubes.

Methodology and Results

• Blood samples from the subjects were collected for 30 minutes post injection of BSP and ICG.
• BSP and ICG are organic anions that are respectively conjugated with glutathione and non-conjugated in the liver.
• The data showed an increase in plasma bilirubin concentration in all subjected animals from 1.03 mg/dl to 3.49 mg/dl due to fasting.
• The clearance rates for both BSP and ICG, derived from kinetic values of their disappearance, showed a decrease post-fasting. Plasma clearance of BSP decreased by 48% and that of ICG by 55% after the 3-day fast.

Conclusion and Comparison with Previous Studies

• The study concludes that fasting significantly decreases hepatic conjugating capacity, observable through reduced plasma clearance of BSP and ICG.
• The researchers found that the decrease in conjugating capacity during fasting is similar to results in dogs, cats, rats, and humans.
• These findings suggest that despite being conjugated with different substrates, both BSP and ICG underwent similar reductions in plasma clearance due to fasting, reinforcing the study’s hypothesis.