The concentration maximum concept in intravenous cholangiography.

The excretion of ioglycamate in the bile of the rhesus monkey was measured at 5% and at 100% bile diversion following an intravenous bolus injection of ioglycamate. At 100% diversion the bile volume was reduced and the concentration of ioglycamate was increased, but the quantity excreted was unchanged. A similar study using iodipamide reported previously gave the same result. When the ioglycamate was given by intravenous infusion, the effect of 100% bile diversion was quite different. The concentration of ioglycamate in the bile was unchanged by the bile diversion but the excretion was reduced. These results indicate that the transport maximum for the excretion of ioglycamate in bile is not a constant and is reduced by interruption of the enterohepatic circulation of bile salts. The maximum concentration of ioglycamate in bile was constant and was independent of the reduction in bile salt output produced by 100% bile diversion. Following a single bolus injection however, the reduction in bile flow produced by 100% bile diversion increased the biliary concentration of ioglycamate. These results suggest that the excretion of ioglycamate is limited by a maximum concentration rather than a transport maximum. The maximum rate of transport (Tm) is dependent on two factors--the maximum concentration of ioglycamate in the bile and the rate of bile flow. The maximum concentration is achieved by an infusion technique and not by a single bolus injection and this supports the view that an infusion technique should be used for intravenous cholangiography.