Cardiovascular and biochemical effects of L-DOPA in the sea-gull, Larus argentatus

We have investigated the effects of L-DOPA alone and in combination with three different inhibitors of L-aromatic aminoacid decarboxylase (DC), carbidopa, benserazid and α-monofluoromethyldopa (MFMD) on blood pressure (BP) and catecholamine content in conscious or anaesthetized sea-gulls, Larus argentatus. The results show that L-DOPA, given i.p., is taken up and decarboxylated to dopamine (DA) in brain and heart. Carbidopa inhibits the peripheral synthesis of DA from exogenous L-DOPA while central decarboxylation is enhanced when compared to the effects of L-DOPA alone. Benserazid and MFMD inhibit both central and peripheral formation of DA after L-DOPA injections. L-DOPA given alone leads to a slight increase in BP, while heart rate (HR) decreases somewhat. After peripheral inhibition of DC using carbidopa, L-DOPA elicits a reduction in BP both in conscious and anaesthetized birds. HR is significantly reduced in anaesthetized birds. Pretreatment with benserazid or MFMD abolishes the cardiovascular effects of L-DOPA. It is concluded that L-DOPA lowers the BP via activation of central mechanisms.