Serum-monoamine-oxidase levels during levodopa therapy

"On-off" effects in patients with Parkinson's disease on chronic levodopa therapy

Fluctuations in performance in patients with Parkinson's disease on chronic levodopa therapy (the "on-off" effect) are due to several factors. The increasing severity during treatment of early morning akinesia, "freezing" episodes, and end-of-dose deterioration are probably due to progression of the underlying disease. Peak-dose dyskinesia and peak-dose akinesia are due to levodopa over dosage. "Yo-yo-ing", which is the severest form of such fluctuation in mobility and dyskinesias, may represent the sum of these disorders.

Effects of morphine on the turnover of brain catecholamines and serotonin in rats-acute morphine administration

Morphine increased the rate of brain dopamine (DA) depletion when given before alpha-methyl-p-tyrosine (AMT) or alpha-propyl-dopacetamide, but not when given after AMT. No effect of morphine was found on the rate of depletion of brain noradrenaline (NA) or serotonin (5-HT) after the two synthesis inhibitors. The accumulation of homovanillic acid and 5-hydroxy-indoleacetic acid induced by probenecid was significantly increased by morphine pretreatment, whereas the accumulation of 3-methoxy-4-hydroxy-phenylglycol sulphate was not changed. These findings can be best explained by the hypothesis that morphine increases the non-functional intraneuronal catabolism of newly synthesized DA and 5-HT, without much effect on the monoamines already taken up in the synaptic vesicles. NA turnover does not seem to be changed by acute morphine administration.

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.