Experiments on the effect of carbon monoxide on aminolevulinic acid dehydrase (ALAD)

The inverse relationship between blood lead concentration and aminolevulinic acid dehydrase (ALAD) is well known. Recently, it has been suggested that a similar relationship exists between carboxyhemoglobin (COHb) and ALAD activity. This study was undertaken to examine more closely the possible effect of carbon monoxide on ALAD. Blood from 19 human volunteers was analyzed for both carboxyhemoglobin and ALAD activity. Smokers had significantly lower concentrations of ALAD than nonsmokers and a rise in carboxyhemoglobin concentration was assocaited with a fall in ALAD activity. The in vitro bubbling of carbon monoxide into human blood did not significantly effect ALAD activity. Four groups of rats (10 per group) wre exposed to carbon monoxide or dietary lead acetate according to the following design: (I) Control--no Pb or CO; (II) 500 ppm Pb acetate in diet; (III) 250 ppm CO four hours/day X 5 days/week X 4 weeks; (IV) Both Pb and CO. Analysis of the rat data showed a significant depression of ALAD by lead. The activity of ALAD in the rats exposed to CO was significantly increased suggesting the possibility of an adaptive phenomenon.