Physiological behavior of I¹³¹-labeled compounds for the study of cardiac output

¹ Department of Research, Miami Valley Hospital, Dayton, Ohio

Radioiodinated diiodo-p-aminohippuric acid (DI¹³¹PAH) and N-(2,4-diiodo-3-hydroxyphenyl) urea (DI¹³¹HPU) were synthesized and examined for their potential usefulness in measuring the cardiac output in animals. These labeled compounds were injected intravenously into rats, rabbits and 13 dogs for study. The average rate of disappearance of DI¹³¹PAH from the blood stream of dogs was 50% and 90% in 1.0 and 6.9 minutes, respectively. Only a very small percentage of the injected radioactivity localized in the tissues, with approximately 0.5% in the thyroid at 24 hours. Under appropriate conditions of the experiment, more than 90% of the injected radioactivity was recovered in the excreta. Cardiac output values determined with DI¹³¹PAH on dogs were reproducible and in the range of reported values determined with other materials.