Central action of L-DOPA in blood pressure regulation and effect on catecholamine content in the frog, Xenopus Laevis

1. We have investigated the effect of L-DOPA and the combination of L-DOPA and two inhibitors of L-aromatic-amino acid decarboxylase (DC), carbidopa and benserazid, on the blood pressure and catecholamine (CA) content in the clawed frog, Xenopus laevis. 2. We conclude that dopamine (DA) is formed from L-DOPA in the heart and brain and that carbidopa reduces the synthesis of DA in the heart but has a poor penetration of the blood-brain barrier (BBB). 3. We find that benserazid inhibits the DA synthesis from L-DOPA in the brain and reduces the synthesis in the heart. 4. L-DOPA in combination with carbidopa lowers the blood pressure significantly (maximum decrease after 1 hr). 5. When L-DOPA is given after pretreatment with benserazid the decrease in blood pressure is abolished. 6. L-DOPA alone does not affect the blood pressure. 7. Our results indicate a central mode of action of L-DOPA lowering blood pressure.