Mechanism of bilirubin excretion by avian kidney

¹ Departments of Medicine, Duke University Medical Center, and Veterans Administration Hospital, Durham, North Carolina

Renal mechanisms of bilirubin excretion were evaluated during an infusion of either nonconjugated (crystalline bilirubin suspension) or conjugated bilirubin (human bile) into one leg vein of the chicken according to the technique of Sperber (Nature 158: 131, 1946). Progressive elevation of the systemic plasma concentrations of total and direct-reacting bilirubin was always associated with the prompt appearance of bilirubinuria. Urine bilirubin consisted solely of the direct-reacting component, and neither plasma nor urine bilirubin was ultrafilterable. Despite the production of dissimilar peritubular plasma concentrations of the two test substances, unilateral differences of bilirubin excretion were not observed. Changes of bilirubin excretion directly paralleled those of estimated "filtered" load in all instances. Although the exact mechanism is unclear, the results indicate that the excretion of direct-reacting bilirubin is determined by glomerular function alone. Evidence of a tubular secretory system was not obtained.