Facilitation of hepatic uptake of phenol 3,6-dibromphthalein disulfonate by taurocholate

The influence of sodium taurocholate (TC) on the hepatic uptake of phenol 3,6-dibromphthalein disulfonate (dibromosulphophthalein, DBSP) was examined in the dog. Single injections of DBSP (7.5-83.3 mg-kg-1) were given intravenously and the initial velocity of uptake (V) of the dye was calculated from the plasma disappearance rate measured during the 1st 5 min. It was observed that: a) the initial velocity of uptake of DBSP increased with the dose (D) in a nonlinear way, a finding consistent with Michaelis-Menten kinetics; the maximal initial velocity of uptake (Vmax) was 7.5+/-1.0 (SD) mg-min-1-kg body wt-1, and the half-saturation constant (Kd) was 27.7+/-7.0 (SD) mg-kg-1; b) when a TC infusion was given prior to the DBSP injection, the initial disappearance of the dye was more rapid than in the absence of the bile acid; Vmax increased to 12.3+/-2.0 (SD) mg-min-1-kg-1 (P less than 0.001) and Kd increased to 50.3+/-12.8 (SD) mg-kg-1 (P less than 0.001). These results indicate that: 1) the uptake of DBSP by the liver cell is a saturable process; 2) TC increases both the Vmax, suggesting a facilitation of the uptake process, and the Kd, suggesting competition for a common site. This effect of TC on DBSP uptake is similar to the previously described effect of this bile salt on BSP excretion into bile and suggests an interaction of bile salts with the uptake process of dyes.