1974. The enhancement of maximal bilirubin excretion with taurocholate-induced increments in bile flow. Can. J. Physiol. Pharmacol. 52,[389][390][391][392][393][394][395][396][397][398][399][400][401][402][403] Of the processes involved in the handling of a bilirubin load, the biliary secretory maximum or T,,, for bilirubin has been regarded as rate limiting, and as a characteristic of liver function. In the present study, bile flow was varied by use of bile acid infusions, in order to determine whether the T,,, is indeed constant or whether it varies with flow. Anesthetized dogs, with bile flow stabilized by cholinergic blockade, were studied during taurocholate infusions. In these animals the ductular conlponent of flow is relatively inhibited and the bile flow rate increases approximately in proportion to the rate of excretion of taurocholate. The maximal biliary excretion rate of bilirubin was found to increase linearly with flow and taurocholate excretion, in a significant fashion, but, in contrast to the relation between taurocholate excretion and flow, a significantly large intercept remained on linear extrapolation towards zero flow. The basis for the large intercept is a great increase in the bilirubin concentration in bile as the flow is decreased. This results in a simultaneous sharp increase in the molar ratio (bilirubin/taurocholate) at very low flow rates.