AJP - Gastrointestinal and Liver Physiology, Vol 268, Issue 5 754-G763, Copyright © 1995 by American Physiological Society
Mechanism of bile acid facilitation of biliary protoporphyrin excretion in rat liver
M. M. Berenson, M. Y. el-Mir and L. K. Zhang
Veterans Affairs Medical Center, Salt Lake City, Utah, USA.
The mechanism(s) by which bile acids increase biliary protoporphyrin
excretion was characterized using perfused rat livers. We determined 1)
relationships between biliary bile acids, phospholipid, and protoporphyrin,
using rapid kinetic analyses; 2) protoporphyrin excretion in livers with
defective canalicular multispecific organic anion transport; 3) effects of
intracellular vesicular transport inhibition with colchicine and monensin;
and 4) the role of luminal bile acids, using retrograde intrabiliary
taurocholate injections. Biliary protoporphyrin excretion peaked with
phospholipid excretion 14-18 min after loading. Protoporphyrin excretion
induced by taurocholate was not related to effects on intracellular
transport, including colchicine- and monensin-inhibitable vesicular
systems. Eisai hyperbilirubinemic rat livers excreted protoporphyrin
similarly to controls. Retrograde intrabiliary taurocholate injections
increased protoporphyrin output. Collectively, these data suggest that 1)
intracellular protoporphyrin transport is mediated by nonvesicular carriers
targeted to the canalicular membrane, and 2) bile acid facilitates
protoporphyrin translocation into bile in the same manner it effects
phospholipid excretion.
