Cardiac delta-aminolevulinic acid synthetase activity. Effects of fasting, cobaltous chloride and hemin

Cardiac delta-aminolevulinic acid (ALA) synthetase activity was studied in animals that had been fasted. The kinetics of the decline in cardiac ALA synthetase activity were measured for 48 hr after food was withdrawn from rats. A marked rate of decrease in activity was observed between 12 and 24 hr. Cardiac ornithine decarboxylase activity also decreased in fasted rats, but cardiac tyrosine aminotransferase activity remained unchanged. Cardiac ALA synthetase activity also decreased in fasted mice but did not decrease significantly in fasted guinea pigs or fasted rabbits whose activites were low even in the fed state. Cobaltous chloride administration caused a marked decrease in cardiac ALA synthetase activity which remained low for a longer duration of time than has been observed in rat liver. The administration of hemin, which causes a marked decrease in hepatic ALA synthetase activity. had no effect on cardiac ALA synthetase activity. The difference in the responses of hepatic and cardiac ALA synthetase activities to hemin administration and food deprivation suggests differential regulation of ALA synthetase activity in heart and liver.