Alterations in hepatic δ-aminolevulinic acid synthetase and heme oxygenase activities after chronic ethanol consumption in rats

Abstract

In the present study, the effect of chronic ethanol consumption in rats on the hepatic heme metabolism was investigated. Male Wistar rats were fed a nutritionally adequate liquid diet containing ethanol as 36% of the total calories for 5 weeks. After an overnight fast, the livers were excised and centrifuged to obtain mitochondrial and microsomal fractions. Chronic ethanol feeding of rats resulted in about 19% hepatomegaly as represented by the increased liver/body weight ratio. There was no difference in the mitochondrial protein content between the ethanol-treated and control rats, but the microsomal protein content was significantly increased in the ethanol-treated rats. Hepatic microsomal content of cytochrome P-450 (P-450) was markedly enhanced by chronic ethanol ingestion. Microsomal contents of cytochrome b5 (b5) and total heme were also increased to a lesser extent. After chronic ethanol abuse, the hepatic activity of delta-aminolevulinic acid (ALA) synthetase, which is a rate-limiting enzyme for heme production, was significantly increased and that of the heme oxygenase was slightly increased. These data indicate that ALA synthetase activity is induced by the negative feedback mechanism in order to compensate the depletion of heme caused by the utilization of heme for P-450. It is also speculated that, in response to excessive production of heme as described above, heme oxygenase activity is secondarily induced to regulate the amount of heme.