Voluntary drinking of ethanol by the rat: biogenic amines and possible underlying mechanism

The present study evaluates the possible relationship between certain biogenic amine metabolites-produced changes in voluntary drinking of ethyl alcohol (ET) solution by the rat and their in vivo effects on the enzymes primarily involved in the hepatic metabolism of ET, i.e., liver alcohol-(L-ADH) and aldehyde dehydrogenase (L-ALDH). In experiments on voluntary intake of ET solution by the rat, compounds selected were injected, 0.5 mM/kg, IP. Administration of vanillylmandelic acid (VMA) and 5-hydroxyindoleacetic acid (5HIAA) and homovanillic acid (HVA) markedly reduced ET drinking. Similar significant effects were seen after administration of the neutral metabolites of the biogenic amines tested, after injection of metanephrine or 3-methoxy-4-hydroxyphenylpyruvic acid. Threodihydroxyphenylserine but not L-dopa reduced ET intake by the rat. Treatment with peripheral decarboxylase inhibitors, i.e., carbidopa, 50 mg/kg, IP, significantly reduced ET drinking as contrasted with nonsignificant decline in ET consumption following benserazide, 500 mg/kg, IP. In the biochemical study, short-term administration of the compounds selected produced varied effects on L-ADH and L-ADH. It is suggested that alteration of hepatic ADH by the compounds tested might account for the observation reduced ET drinking thereby, indicating the contribution of peripheral sources rather than central factors in mediating the behavioral effects studied.