Delta-Aminolevulinic acid synthetase in the heart.

The regultion of cardiac delta-aminolevulinic acid synthetase activity was studied in rat heart homogenates. Optimal conditions were determined for the measurement of delta-aminolevulinic acid and an appropriate assay was established for the heart. The activity of cardiac delta-aminolevulinic acid synthetase was determined in rats either fed ad libitum or starved for 24 or 48 h. Marked decreases in delta-aminolevulinic acid synthetase activity were observed in homogenates or mitochondrial fractions prepared from hearts of fasted animals and an explanation for previous findings that the enzyme is undetectable in heart tissue is provided. Dexamethasone treatment was effective in reversing the decreases brought about by fasting but had no effect on the delta-aminolevulinic acid synthetase activity in heart homogenates from fed rats. ACTH treatment had no effect in fed or starved rats. Decreases in delta-aminolevulinic acid synthetase activity induced by fasting were not reversed in homogenates or mitochondrial preparations by succinyl-CoA-generating systems or when alpha-ketoglutarate was substituted for succinate in homogenate preparations. Cardiac delta-aminolevulinic acid dehydratase levels are not altered by fasting. Agents such as allylisopropylacetamide or 3,5-dicarbethoxy-1,4-dihydrocollidine, which produce marked increases in hepatic delta-aminolevulinic acid synthetase activity, have no effects on the activity of this enzyme in the heart.