Effect of chronic L-DOPA administration of catecholamine metabolism in the rat.

1. L-DOPA was administered to rats by twice daily intraperitoneal injection for a period of eleven days. The daily dose was gradually increased from 250 mg/kg to 1 g/kg. The animals were killed 12 h after the last injection and tissue catechol-O-methyl transferase, DOPA-decarboxylase and monoamine oxidase activity determined.2. Catechol-O-methyl transferase activity was reduced in the liver (46%) and red blood cells (38%) but was approximately doubled in the heart.3. Liver DOPA-decarboxylase activity was reduced by approximately 25%.4. L-DOPA administration did not significantly affect the activity of any of the enzymes studied in brain tissue.