Increased δ-aminolevulinic acid synthetase activity in rat ventricle after acute exercise

Endurance-type training can cause a moderate cardiac hypertrophy. Concurrent with the enlarged cardiac mass is a proportional increase in mitochondrial components, e.g., the cytochromes. Since the cytochromes are heme-containing proteins, an increase in heme biosynthesis might be expected to occur during the development of the cardiac hypertrophy. Delta-aminolevulinic acid (ALA) synthetase, the rate-limiting enzyme for heme biosynthesis, was measured in rat ventricles to evaluate this possibility. ALA synthetase activity was monitored at various times after a 90-min treadmill run in previously unexercised male rats since cardiac enlargement is initiated after a single exercise bout. There was a significant (P < 0.01) increase in the activity of this enzyme for the period between 2 and 8 hr postexercise. This elevation in ALA synthetase activity then declined to control values by 16 hr postexercise. In contrast, animals trained for a sufficiently long time to fully develop cardiac hypertrophy did not demonstrate a rise in ALA synthetase activity after a similar exercise bout. This increase in ALA synthetase activity in previously unexercised animals suggests that heme biosynthesis may be accelerated following exercise in these animals. This heme production could support an increased cytochrome production that may be needed during the development of the exercise-induced cardiac hypertrophy. The lack of response in the trained animals where a modest cardiac enlargement (8%) was already evident adds support to this suggestion.