In vivo relationship between monoamine oxidase type B and alcohol dehydrogenase: effects of ethanol and phenylethylamine.

The role of acute ethanol (2.5 g/kg i.p.) and phenylethylamine (100 mg/kg i.p.) on the brain and platelet monoamine oxidase activities, hepatic cytosolic alcohol dehydrogenase, redox state and motor behaviour were studied in male rats. Ethanol on its own decreased the redox couple ratio, as well as, alcohol dehydrogenase activity in the liver whilst at the same time it increased brain and platelet monoamine oxidase activity due to lower Km with no change in Vmax. The elevation in both brain and platelet MAO activity was associated with ethanol-induced hypomotility in the rats. Co-administration of phenylethylamine and ethanol to the animals, caused antagonism of the ethanol-induced effects described above. The effects of phenylethylamine alone, on the above mentioned biochemical and behavioural indices, are more complex. Phenylethylamine on its own, like ethanol, caused reduction of the cytosolic redox ratio and elevation of monoamine oxidase activity in the brain and platelets. However, in contrast to ethanol, this monoamine produced hypermotility and activation of the hepatic cytosolic alcohol dehydrogenase activity in the animals. The results suggest that some of the toxic actions of ethanol in rats may be mediated through the activation of monoamine oxidase type B, with the consequent depletion of the endogenous levels of phenylethylamine. The data appear to support the concept of phenylethylamine involvement in affective disorders.