Iodinated cholylglycyltyrosine: a new agent for hepatobiliary imaging

The characteristics of radiolabelled cholylglycyltyrosine (CGT), a recently synthesised bile acid, were studied. 125I-CGT-Na was found to have a short plasma half-life of 1.6 +/- 0.4 min in rats and 3.1 +/- 0.7 min in dogs. Biliary clearance studies showed the cumulative biliary output of the tracer over 20 min in rats to be 95.7% of the total dose administered, with a mean biliary transit time (50% retention time) of 4.0 +/- 0.1 min, i.e. similar to the biliary kinetics of taurocholate. 131I-CGT-Na proved to be satisfactory for hepatobiliary imaging in rats and dogs at doses of 35 microCi (1.3 MBq) in rats and 90 microCi (3.3 MBq) in dogs. Satisfactory hepatic images were also obtained in rats that had high bilirubin levels produced by obstruction or the recycling of bile. These results show that CGT has better pharmacokinetics than currently used hepatobiliary imaging agents, and that this new compound may be useful in scintigraphy even in the presence of jaundice.