Postnatal changes in enzyme activities of rat myocardial adenine nucleotide catabolic pathway

Three catabolic enzymes, 5'-nucleotidase (5'NT), adenosine deaminase (ADA), purine nucleoside phosphorylase (PNP) and one anabolic enzyme, myokinase (MK) involved in adenine nucleotide (AN) metabolism were studied in myocardium from 4 to 105 day old rats. The specific enzyme activities (nmoles/min/mg protein) at day 4 were 35.3 for 5'NT, 28.4 for ADA, 43.3 for PNP, and 5 X 10(3) for MK. At day 7, 5'NT, activities rose to 450%; PNP and ADA 150%; and MK 120%; of the day 4 level. The activities of the three catabolic enzymes were elevated for one or two weeks then declined rapidly. By day 34, they were slightly above the adult values. MK activity displayed a different time course. It continued to increase slowly with age after the initial surge. Compared to the adult heart, the total activities of these catabolic enzymes in the one- to three-week-old heart were 30% to 220% higher. This transient elevation in AN catabolic enzyme activities may be related to active DNA synthesis and cell proliferation occurred in the rat myocardium during the same period.