Effect of interruption of the enterohepatic circulation of bile on the secretion of iodipamide in the bile of the rhesus monkey

Pharmacokinetics of iodoxamic acid in rhesus monkey: biliary excretion, plasma protein binding, and enterophepatic circulation

The previously reported steady-state method allowed estimation of the capacity-limited pharmacokinetics of the cholangiographic agent, iodipamide. To circumvent the long time period required to establish each steady-state level, a dynamic method was applied to the study of the rate processes involved in the hepatic uptake and biliary excretion of a new cholangiographic agent, iodoxamic acid, in rhesus monkeys. The dynamic method has the advantage that the pharmacokinetic parameters involved in capacity-limited hepatic uptake or biliary excretion can be obtained from a single infusion experiment. The V max was 1.03 +/- 0.25 mumoles/kg/min (mean +/- SD); Km varied from animal to animal and ranged from 1.5 to 16.4 micrometer. Protein binding was estimated using equilibrium dialysis. The Freundlich isotherm yielded a linear plot when the natural logarithm of unbound iodoxamic acid concentration in plasma was plotted against the natural logarithm of its blood concentration. The plasma protein binding data also could be fitted to the Langmuir isotherm, presuming two independent classes of binding.

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.

Improvement of biliary excretion of ioglycamide by pretreatment with phenobarbital

The influence of a phenobarbital pretreatment on the distribution and biliary excretion of Ioglycamide was studied in 6 experiments in the anaesthetized minipig. The phenobarbital pretreatment led to a significant increase of the biliary transportmaximum and the biliary concentration of Ioglycamide. A detailed analysis suggests a phenobarbital induced stimulation of the hepatocellular excretion. The applicability of a pretreatment with phenobarbital in order to improve the opacification of the biliary system during x-ray-examinations with Ioglycamide is discussed.

[On the mechanisms of biliary excretion of the biliary contrast medium ioglycamide in the mini-pig with special regard of the importance of the bile flow (author's transl)]

16 experiments were performed in order to investigate the mechanisms of biliary excretion of Ioglycamide in the mini-pig. The results confirm the mechanisms known from other species for this experimental animal. Additionally, however, they demonstrate a significant linear correlation between the spontaneous bile flow and the biliary transport-maximum of Ioglycamide. It is concluded that this correlation is due to the fact that the bile flow as well as the transport-maximum represent independent parameters of the excretory capacity of the liver cells. This conclusion is supported by further experiments that were unable to show an improvement of the biliary transport-maximum of Ioglycamide by stimulation of the bile flow during infusions of bile acids and secretin. These results prove the impossibility to enhance the biliary excretion of Ioglycamide by stimulation of bile flow. This, however, indicates that it is possible to dilute or concentrate the biliary Ioglycamide concentration by induced variations of bile flow, a fact that might become important to improve the efficiency of i.v. cholegraphy.

Levels of ioglycamate (Biligram) in the bile of the rhesus monkey following intravenous infusion at different dose-rates

The maximun rate of excretion of ioglycamate in the bile of the rhesus monkey was achieved when the rate of adminstration was at least twice the rate of excretion. A maximum concentration of ioglycamate in the bile was also established, and this is more important to the visualization of the bileducts than the quanity of ioglycamate excreted. The maximum concentration was obtained at the same rate of infusion as that which produced the maximum rate of excretion. The peak concentration was sustained longer with an infusion lasting two hours than with one lasting 36 minutes, althought the same quanity of ioglycamate had been administered. It is concluded that an infusion at a rate equal to twice the maximum excretory rate and continued for two hours or longer is a rational approach to intravenuous cholangiography particularly in those patients where there has been some diffculty in bile-duct visulization.