Splenic Origin of Early-Labeled Bilirubin in Rats Exposed to High Altitude 1

Abstract

Abstract

The formation of early-labeled [¹⁴C]bilirubin (ELB) from the pulse-injected heme precursor, [2-¹⁴C]glycine was measured in rats. Chronic exposure to a simulated altitude of 18,000 ft increased the rate of ELB formation two- to three-fold over that in sea level controls for periods of up to 40 hr following precursor injection. Splenectomy significantly reduced the rate of ELB formation in altitude-exposed rats in the 0- to 5-hr interval after precursor injection, but splenectomy had no effect in sea level controls. Conversely, hypoxia increased the rate of ELB excretion in splenectomized rats in the 10- to 20-hr interval after precursor injection, but not at earlier time intervals. These results are consistent with our previous hypothesis that an exaggerated splenic erythropoiesis with both effective and ineffective components develops in the rat as a result of chronic exposure to extreme altitude.