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Abstract
This study deals with the effects of dopamine (DA), L-dopa, carbidopa and L-dopa/carbidopa on immuno-inflammatory skin reactions in the rat. For this purpose, male Wistar rats immunized with bovine serum albumin in Freund's adjuvant were treated subcutaneously with different doses of DA, L-dopa, carbidopa and L-dopa/carbidopa, for a period of 14 consecutive days or 3 days before skin-testing with BSA. An additional group of rats received 1 injection of a dopamine-related drug 4 hours before and 1 injection 4 hours after skin-testing. Corresponding controls were treated with saline. Arthus and delayed hypersen-sitivity skin reactions were read at 4 and 24 hours respectively. The results showed that repeated injections of DA, L-dopa and L-dopa/carbidopa significantly suppressed Arthus and delayed reactions. The highest suppression was recorded in rats treated with L-dopa plus carbidopa. Concerning the dose required for immunosuppression it appears that DA was the most effective. Carbidopa did not affect hypersensitivity skin reactions. These results suggest the in vivo relationship between dopamine-related compounds (L-dopa and DA) and immuno-inflammatory reactions. Most probably, L-dopa when is given alone converts into DA and this increase of DA content in periphery depresses immune reactions. However, L-dopa given together with carbidopa (an enzyme which prevents decarboxylation of L-dopa into DA, and enables the penetration of L-dopa into CNS) augments the content of DA in the brain and thus affects immune responses. It appears, therefore, that L-dopa and DA act both peripherally and centrally on immune responsiveness.