TAURO ALPHA-MURICHOLATE HAS A BILIARY TRANSPORT MAXIMUM (TM) VALUE EQUIVALENT TO THAT FOR TAUROURSODEOXYCHOLATE AND TAURO BETA-MURICHOLATE IN THE RAT

Our previous studies have shown that Tm values for tauroursodeoxychola te (TUDC) and tauro beta-muricholate (T beta-MC) are more than twofold higher than that for taurocholate (TC) in the rat. The present study attempted to clarify whether tauro alpha-muricholate (T alpha-MC) also has such an unusually large Tm value in the rat. Under nembutal anest hesia, male Wistar derived rats (body weight 280-300 g, 13 wks in age) were continuously infused with T alpha-MC solution. The infusion rate was raised stepwise every 20 min, until the bile flow began to declin e. Bile was collected every 10 min and bile salt excretion rate was de termined. The average of the highest three excretion values was assume d to be the Tm in each animal. The Tm value of T alpha-MC was found to be 2.86 +/- 0.36 mu mol/min/100 g (mean +/- SD, n=4), which was even greater than Tm values for TUDC (2.59 +/- 0.39 mu mol/min/100 g, n=4) and T beta-MC (1.93 +/- 0.31 mu mol/min/100 g, n=4) as we reported pre viously. The relationship between the bile flow rate (mu l/min/100 g, Y axis) and bile salt excretion rate (mu mol/min/100 g, X axis) was hi ghly linear [Y=(6.00 +/- 0.29) X + (6.60 +/- 1.88), P < 0.001, r=0.95, n=54]. The slope value for T alpha-MC (6.00 +/- 0.29 mu l/mu mol) was significantly higher than that for TUDC (4.76 +/- 0.71 mu l/mu mol) a nd was comparable to that for T beta-MC as we previously found for the se bile salts in this rat strain. The results suggest that T alpha-MC has a very efficient transport system in this species as was observed for the other two bile salts that have a 7 beta-hydroxy group (TUDC an d T beta-MC). This efficient transport system thus appears to be share d not only by bile salts specifically having a 7 beta-hydroxy group, b ut also by other bile salts such as T alpha-MC that have a 6 beta-hydr oxy group but not a 7 beta-hydroxy group.