Employing the in situ perfused rat liver, we examined the origins and mechanisms of transport of proteins into bile. First, utilizing polyacrylamide gels, we noted that many biliary proteins co-migrated with dominant serum proteins. Upon liver perfusion with serum-free medium, most proteins disappeared from the biliary profile; one major biliary protein that was not present in serum, identified as secretory component, remained. Kinetic analysis of the disappearance half-lives of the biliary proteins suggested that some serum proteins enter bile by a slow (20 to 30 min; transcellular) route, while others utilize both slow and rapid (5 min; paracellular) routes. In biosynthetic labeling experiments, secretion of newly synthesized proteins into bile was delayed about 20 min when compared with secretion of proteins into the perfusion medium and comprised less than 1% of the total secreted proteins. When a new liver was inserted into the perfusion medium containing newly synthesized secreted proteins, only two proteins, hemopexin and an unidentified protein, were transported into the bile from the perfusion medium; other biliary proteins were presumed to come directly from the hepatocyte. This latter group included some proteins that were secreted into the perfusion medium as well as into bile, and others, e.g., secretory component, that were secreted only into bile. Based on our results we have defined six pathways for entry of proteins into bile.

Cimetidine inhibits oxidative drug metabolism; it is not known whether this drug alters the catabolic fate of hepatic heme. We therefore investigated hepatic heme turnover both by a14CO breath test and directly by labeling the heme pool. Neither acute (150 mg/kg i.p.) nor chronic (150 mg/kg i.p. bid for 3 days) cimetidine administration significantly affected hepatic heme turnover. Chronic, but not acute, cimetidine significantly (p<0.025) increased heme oxygenase activity. Cimetidine inhibited heme oxygenase activity in vitro at concentrations achieved in vivo.

In the rat hepatocyte, the internalization and degradation of asialoglycoproteins and the secretion of plasma and biliary proteins require specific intracellular sorting of vesicles. To aid in the biochemical characterization of these different vesicular pathways, we examined the effects of the ionophore monensin on the uptake and degradation of 125I-asialoorosomucoid (ASOR) and on the secretion of plasma and biliary proteins by the in situ perfused rat liver. In control livers, 77% of injected 125I-ASOR was extracted on first pass; 93% of the extracted radioactivity was released back into the circulation (totally degraded and some intact ASOR was found); and approximately 2% was recovered in the bile, some of which was intact. Monensin treatment decreased first pass uptake of 125I-ASOR to 57% and abruptly blocked the release of radioactivity into the perfusate and the bile. When hepatic proteins were biosynthetically labeled with 3H-leucine, monensin treatment dramatically reduced and delayed the secretion of newly synthesized proteins into both the perfusate and the bile. In contrast with control livers, in which secretion of protein into the perfusate preceded secretion of protein into the bile, TCA-precipitable 3H-protein appeared in bile about 20 min before TCA-precipitable 3H-protein appeared in the perfusate in monensin-treated livers. Thus, monensin treatment in the perfused liver blocked the degradation of asialoglycoproteins and inhibited the secretion of plasma proteins but had less effect on biliary protein secretion. These data document physiologic effects of monensin in an intact organ and suggest that biochemical distinctions between different vesicular pathways exist in the rat hepatocyte.

The hepatic uptake of polymeric immunoglobulin A (IgA) is mediated by secretory component; the resulting secretory IgA is excreted intact into bile. To define the hepatic metabolism of polymeric IgA, we quantitated the uptake and transport of human polymeric IgA1 after a single pass through the perfused rat liver. Uptake of polymeric IgA1 was compared with that of asialoorosomucoid, a glycoprotein whose uptake is mediated by the asialoglycoprotein receptor. Single-pass hepatic uptake of 125I-polymeric IgA1 and of 125I-asialoorosomucoid averaged 18.0 +/- 3.1% (SE) and 71.8 +/- 2.8%, respectively. The uptake of 125I-polymeric IgA1 was inhibited by excess unlabeled polymeric IgA1 but not by asialoorosomucoid. Only 13.0 +/- 1.6% of the 125I-polymeric IgA1 extracted by the liver was excreted into bile, whereas three-fourths was released into the hepatic venous effluent in degraded form. Thus, both the uptake and biliary excretion of polymeric IgA1 by the rat liver are inefficient processes. Polymeric IgA1 follows two distinct pathways after uptake by the liver: a small proportion is excreted intact into bile, while the majority is degraded and released back into the circulation.

Two cases of aphthous ulceration apparently due to diversion colitis are described. There was no evidence of Crohn's disease initially or at follow-up. Aphthous ulceration of the colon and diversion colitis are reviewed, and the nonspecificity of aphthae for Crohn's disease is stressed. The presence of aphthous ulcers in a diverted colon should not preclude colostomy closure.

The common bile duct of male Sprague-Dawley rats was cannulated with either PE 10 or PE 50 tubing. Maximal secretory rate of taurocholate averaged 389±67 (SD) and 657±115 nmoles·min−1·g liver−1 in the PE 10 and PE 50 group, respectively (p<0.005). Maximal bile secretory pressure was significantly higher in the PE 10 group (240±28 vs 174±8 mm H20; p<0.005). When the maximal secretory rate was exceeded, bile flow decreased in both groups but this was accompanied with a decrease in maximal bile secretory pressure in the PE 10 group only. Maximal secretory rate of bile salts is markedly influenced by experimental technique. Use of small caliber common bile duct cannulae leads to partial obstruction and decreases the apparent maximal secretory rate for taurocholate.

We describe a device for continuous infusion and monitoring of exhaled 14CO as a test of hepatic bilirubin production in rats. A Silastic catheter, implanted into a jugular vein under light ether anesthesia, was protected with a spring shield and a cannula swivel. The animals were kept in a modified Bollman cage. delta-[5-14C]aminolevulinic acid, a heme precursor yielding 14CO upon breakdown of heme to bilirubin, was infused at a constant rate. Exhaled 14CO was oxidized to 14CO2 and collected in ethanolamine. The efficiency of the system averaged 97.8%. In untreated animals 14CO production reached a plateau within 12 h; thereafter, it increased by 2.8% per day. The responsiveness of the system was tested by fasting the animals, which stimulated hepatic bilirubin production. Fasting increased 14CO production by 32.8 +/- 8% (mean +/- SD, P less than 0.005) after 72 h. This was associated with an increase in hepatic heme oxygenase activity (+48%, P less than 0.05) and a decrease in microsomal cytochrome P-450 content (-45%, P less than 0.05). Thus, our approach permits continuous monitoring of hepatic bilirubin production without subjecting the animals to the stress of handling, restraint, or anesthesia. The method can easily be applied to other breath tests involving formation of 14CO2.