Differences of reabsorption of unconjugated BSP and BSP-glutathione from the rat biliary tree after retrograde intrabiliary injection

Involvement of influx and efflux transport systems in gastrointestinal absorption of celiprolol

Gastrointestinal absorption of several beta-blockers is inhibited by citrus juices, although molecular mechanism(s) lying on their small intestinal absorption has not yet been identified. Here, we attempted to demonstrate involvement of both influx and efflux transporters in vivo in gastrointestinal absorption of celiprolol in mice. Plasma concentration of celiprolol (3 mg/kg) after oral administration was mostly under the limit of quantification in wild mice, whereas that in mdr1a/b knockout (mdr1a/b(-/-)) mice was much more obvious, indicating P-glycoprotein-mediated efflux. Then, the oral absorption of celiprolol in mdr1a/b(-/-) mice was further examined to investigate influx transport mechanism with avoiding effect of P-glycoprotein. Coadministration of bromosulfophthalein (BSP), an inhibitor of various influx transporters including organic anion transporting polypeptide (OATP) reduced plasma celiprolol concentration. Inhibition by BSP of celiprolol uptake from apical membranes was confirmed in Ussing-type chamber of small intestinal tissues. Uptake of celiprolol by human small intestinal transporter OATP-A/1A2 was also confirmed in Xenopus Laevis oocytes. Interestingly, OATP-A/1A2 accepts various beta-blockers including acebutolol, atenolol and sotalol, oral absorption of which is inhibited by coadministration of citrus juice or telithromycin in human. Taken together, these findings have suggested fundamental role of influx transport system(s) in oral absorption of celiprolol.

Influence of retrograde volume and short time cholestasis on the biliary reabsorption of sulfobromophthalein sodium (BSP) and phenol 3,6 dibromphthalein disulfonate (DBSP) from the rat biliary tree after retrograde intrabiliary injection (RII)

The retrograde intrabiliary injection (RII) technique was used to study the reabsorption of equimolar doses (1,2 mumol) of sulfobromophthalein sodium (BSP) and its analogue phenol 3,6 dibromphthalein disulfonate (DBSP) from the rat biliary tree under the experimental conditions established in this study i.e. variation of retrograde volumes injected and of short time cholestasis. RII was performed with a microliter syringe joined to a cannula positioned in the proximal third of the common bile duct. This technique guaranteed accurate administration of microliter quantities, also free bile flow could be reinitiated 3 - 5 sec after RII. Bile samples were collected in 2, 5 min intervals up to the 5th min, then in 5 min intervals up to the 15th min, and the following 15 min up to the 30th min and analysed for compounds administered by RII. No significant differences in the biliary reabsorption of BSP and DBSP after RII could be detected. Increasing retrograde volumes of 20, 40, 60, 110, and 160 mul lead to decreasing percent recoveries in the bile in the first 2,5 min after RII (88,0 +/- 3,8 - 15,6 +/- 3,1) when bile flow was started at once after RII. An inverse correlation between retrograde volume and percent recoveries was found. Increasing duration of cholestasis (bile flow was started at once, 0,5 min, 3 min, 6 min, and 30 min after RII) results in decreasing percent recoveries of BSP and DBSP in the first 2,5 min after free bile flow was reinitiated (52,7 +/- 3,6 - 20,0 +/- 1,2). A time dependent proportional effect could be detected. Furthermore in the case of BSP concomitant with increasing cholestasis increasing amounts of BSP - conjugates were found in the bile supporting the idea of a continuing ductular - hepatocellular circulation even during complete obstruction of the common bile duct.

Biliary reabsorption of cholate sodium, glycocholate sodium, and taurocholate sodium from the rat biliary tree after retrograde intrabiliary injection

The results demonstrate the biliary reabsorption of 14C-cholate, 14C-glycocholate, and 14C-taurocholate from the rat biliary tree after retrograde intrabiliary injection. It could be shown that retrograde injection of these bile salts (20 nmol) in a total volume of 40 mul leads to significantly increased biliary reabsorption in contrast to the administration in a retrograde volume of only 20 mul. These differences in reabsorption may be explained by greater reabsorption at a more proximal site in the biliary tree. Furthermore 14C-glycocholate and 14C-taurocholate are reabsorbed to a lesser extent in contrast to 14C-cholate when bile flow was restarted at once after retrograde injection in a volume of 40 mul. It is speculated that conjugation of cholate to glycine and taurine has some effect on the extent of biliary reabsorption of this bile acid. Following the results presented in this paper one might hypothize that biliary reabsorption has an important influence on bile composition i.e. the biliary excretion of bile salts.

Influence of dehydrocholate sodium on the biliary reabsorption of sulfobromophtalein sodium from the rat biliary tree after retrograde intrabilary injection

Bilary re-excretion of sulfobromophthalein sodium (BSP) (1.2 mumol/rat) after retrograde intrabilary injection is markedly inhibited by dehydrocholate sodium (Decholin) given intravenously as a constant infusion (3.1 mumol/min/kg body weight) or as a bolus injection (24.8 mumol/rat) to rats. Most interestingly Decholin demonstrates the same inhibitory effects on the biliary re-excretion of BSP when it is administered by retrograde intrabiliary injection (24.8 mumol/rat) together with the dye. In contrast to the inhibition of biliary re-excretion of BSP its biliary reabsorption from the biliary tract seems to be rather increased: about 80-85% of 1.2 mumol BSP are reabsorbed in all sets of experiments with Decholin in comparison to about 65% to the control group. Combined with histological data it is suggested that reabosorption of BSP after retrograde intrabiliary injection occurs at the ductular site whereas re-excretion takes place at the cannalicular membrane of the hepatocyte.