Studies on heme synthesis in the rat adrenal

The activity and regulation of rat adrenal delta-aminolevulinic acid synthetase (EC 2.3.1.37) has been studied. The activity of delta-aminolevulinic acid synthetase in rat adrenal homogenates is comparable to the activity found in rat hepatic homogenates when untreated animals are employed. Starvation of rats for 24 and 48 hours increased adrenal delta-aminolevulinic acid synthetase activity without altering the hepatic enzyme. The treatment of rats with ACTH gel also increased adrenal delta-aminolevulinic acid synthetase activity. The effect of starvation on rat adrenal delta-aminolevulinic acid synthetase activity appears to be mediated by ACTH and can be prevented by the administration of dexamethasone. Adrenal delta-aminolevulinic acid synthetase appears to be refractory to induction by agents which induce the hepatic enzyme. These results suggest that the adrenal enzyme may be uniquely controlled by neural and endocrine influences which differ from the factors which regulate the activity of the hepatic enzyme.