AJP - Gastrointestinal and Liver Physiology, Vol 242, Issue 4 347-G353, Copyright © 1982 by American Physiological Society
Effect of choleretics on canalicular transport of protoporphyrin in the rat liver
D. L. Avner and M. M. Berenson
The major route of protoporphyrin elimination is biliary secretion. To
clarify the nature of the secretory process, maximal canalicular secretion
of protoporphyrin was determined under basal conditions and after treatment
with various choleretics. The maximal secretion of protoporphyrin under
basal conditions was 0.07 +/- 0.01 micrograms.min-1.100 g body wt-1.
Infusion of physiological amounts of sodium taurocholate increased
protoporphyrin secretion 13-fold (0.90 +/- 0.02), primarily by increasing
the biliary protoporphyrin concentration. Biliary protoporphyrin secretion
tended to plateau in spite of a continued rise in both biliary bile acid
secretion and concentration. Infusion of sodium dehydrocholate increased
protoporphyrin secretion, but to only 35% of that achieved by sodium
taurocholate. Ethacrynic acid and phenobarbital increased bile flow over
controls but failed to enhance protoporphyrin transport. Thus, canalicular
secretion of protoporphyrin was maximally enhanced by micelle-forming bile
acids and unaffected by nonbile acid choleretics. The observed limitation
of protoporphyrin secretion may be related to achievement of a canalicular
transport maximum or to a toxic effect of protoporphyrin on the transport
process.
