Fasting Hyperbilirubinemia and Its Relationship to Free Fatty Acids and Triglycerides in the Horse 1

Abstract Bilirubinemia was studied in eight horses fasted for 5 days and then refed for 5 days. In six healthy horses bilirubin rose from 1.3 ± 0.4 mg/dl (mean ± SD) in fed horses to reach a plateau of 5.3 ± 1.4 mg/dl between 64 and 136 hr of starvation. This was almost entirely due to an increase in the unconjugated bilirubin fraction. On refeeding, serum bilirubin fell to prestarvation concentrations within 2 days. Scleral icterus lagged behind changes in serum bilirubin. There was a strong positive correlation between serum bilirubin and free fatty acids, R 2 = 0.79. This correlation was not improved when differences in serum albumin were considered, so changes in the affinity of albumin for bilirubin are probably not responsible for fasting hyperbilirubinemia. Including serum triglycerides in the regression equation improved its predictive value, R 2 = 0.91. Free fatty acids may influence bilirubin metabolism as a result of competition between free fatty acids and bilirubin for binding to ligandin.