Ontogenesis of uptake and deamination of 5-hydroxytryptamine, dopamine and beta-phenylethylamine in isolated perfused lung and lung homogenates from rats.

1. Uptake of 5-hydroxytryptamine (5-HT) and beta-phenylethylamine (PEA) was studied in perfused lung from male rats between 10 and 70 days old. 2. Monoamine oxidase (MAO) activity towards 5-HT, PEA and dopamine was studied in homogenate preparations of lung from rats aged between 5 and 80 days. 3. Uptake of 5-HT (10 microM) decreased throughout the age range studied but uptake of PEA (50 microM) increased for the first 30 days and beyond this age it decreased. Metabolites formed for both amines reflected the changes in uptake. 4. MAO activity deaminating 5-HT is well developed by day 10 and reaches its maximum by day 40. For dopamine and PEA, MAO activity remained low until day 20, and the developed rapidly, reaching a maximum by day 40 for dopamine; activity towards PEA did not reach a maximum by day 80. 5. These results show that uptake and MAO activity changes with age and thus the lung responds like other tissues. 6. These results also demonstrate the independent development of uptake and MAO activity towards 5-HT, PEA and dopamine.