The in vivo uptake of [3H]isoprenaline by the chick embryonic heart and liver.

Seven-day-old embryos received 3.7 x 10(5) Bq (10 muCi) of [3H]isoprenaline (IPRO) hydrochloride intraamnially. The capacity of myocardial and liver tissue for taking up administered catecholamine increased rapidly during the first 10 min after administration. The peak concentration (disintegrations per minute per milligram) in the heart, however, was significantly lower as compared with the liver. Thereafter the uptake in both organs markedly decreased and reached its lowest values between 15 and 30 min. From then on, the concentration of the tritium-labelled compound increased again and 6 h after administration it attained the second peak in both organs. This value was more than five times higher in the liver as compared with the myocardium. Radiometric evaluation of chromatograms from myocardial and liver extracts has revealed that IPRO is rapidly metabolized to 3-O-methyl IPRO. The proportion of this fraction in both organs represents approximately 40% of total radioactivity as early as 5 min after administration. The time course of IPRO uptake indicates that the following factors may participate in the development of cardiac and hepatic lesions: (a) IPRO immediately after administration, and (b) subsequently its toxic metabolites.