IMAGING OF EXOCRINE PANCREATIC FUNCTION - INVESTIGATION OF THE BIOAVAILABILITY OF WEAK ORGANIC-ACIDS AS POTENTIAL PANCREATIC CONTRAST AGENTS FOR COMPUTED-TOMOGRAPHY

RATIONALE AND OBJECTIVES. The feasibility of targeting iodinated contr ast agents to the exocrine pancreas was investigated. Iodinated weak o rganic acids including succinic acidmono-3-amino-2,4,6-triiodo-N-ethyl anilide (compound I), the ethanolamine salt of N-ethylsuccinic acid-(2 ,4, 6-triiodo-3-methylamino anilide) (compound II), and the sodium sal t of 2,4,6-triiodo-3-N-ethylacetylamino-phenylpropionic acid (compound III) were studied as potential contrast agents for computed tomograph y (CT) of the pancreas. METHODS. An ex vivo perfusion system was used to compare pancreatic uptake of the three compounds. In vivo CT studie s were conducted using domestic pigs to study potential enhancement of the pancreas after intravenous injection of the compound. RESULTS. Ex vivo perfusion studies with isolated rat pancreas demonstrated nearly identical extraction ratios of approximately 0.6 for all three compou nds tested. Average iodine concentrations measured in pancreas at the end of the perfusion studies was 0.27 mg/g +/- 0.20 for compound I, 0. 18 mg/g +/- 0.06 for compound II, and 0.16 mg/g +/- 0.09 for compound III. Differences in iodine concentrations retained were not statistica lly significant. Computed tomography studies in domestic pigs demonstr ated up to 30% enhancement of the pancreas after intravenous injection of 75 and 150 mg/kg of compound II at 45 minutes. Whereas ex vivo per fusion studies indicated increasing extraction of the three compounds with increasing doses/concentrations in the perfusate, no improved con trast enhancement was observed at the higher dose level compared with the lower dose in CT. CONCLUSION. Both ex vivo perfusion studies and d ose-independent enhancement levels achieved seem to indicate a transpo rt maximum in the pancreas for the iodinated weak organic acids studie d.