Effect of L-DOPA on endogenous histamine metabolism.
To estimate the effect of long-term administration of L-3,4-dihydroxyphenylalanine (L-Dopa) on methylation of compounds not formed from it, the urinary excretion of histamine and its methylated metabolites was studied in rats and guinea pigs fed L-Dopa in their diets and in patients with Parkinson's disease being treated with L-Dopa. In the guinea pigs, but not in the rats, L-Dopa administration decreases excretion of histamine and of its methylated metabolites, methylhistamine and 1-methylimidazole-4-acetic acid. Because excretion of 1-methylimidazole-5-acetic acid, which comes from the diet and is not a metabolite of histamine, was unaffected by the L-Dopa treatment, the decreases were due to a specific effect of L-Dopa on histamine metabolism. When compared to normal control subjects, patients with Parkinson's disease excreted less histamine and methylhistamine, both before and during treatment with L-Dopa. Administration of the peripheral aromatic L-amino acid decarboxylase inhibitor, L-alpha-methyldopa hydrazine (MK 486), decreased urinary excretion of histamine markedly. Neither L-Dopa nor MK 486 appeared to influence excretion of the imidazoleacetic acids in the patients. The results suggest that L-Dopa may decrease histamine formation or release in some species but that it does not influence histamine methylation.
D000085:Acetates / Q000652:urine; D000328:Adult; D000368:Aged; D000818:Animals; D002230:Carbidopa / Q000494:pharmacology; D003864:Depression, Chemical; D005260:Female; D006168:Guinea Pigs; D006632:Histamine / Q000652:urine*; D006801:Humans; D007093:Imidazoles / Q000652:urine; D007980:Levodopa / Q000494:pharmacology* / Q000627:therapeutic use; D008297:Male; D008745:Methylation; D008875:Middle Aged; D010300:Parkinson Disease / Q000188:drug therapy / Q000652:urine*; D051381:Rats; D013045:Species Specificity
D000085:Acetates; D007093:Imidazoles; D007980:Levodopa; D006632:Histamine; D002230:Carbidopa