Levodopa-mediated alteration in the activity of pyridoxal kinase in rat basal ganglia.

The acute intraperitoneal administration of 400 mg/kg of levodopa reduced the concentration of pyridoxal phosphate and increased the activity of pyridoxal kinase. The chronic oral administration of 100 mg/kg/day of levodopa did not alter the concentration of pyridoxal phosphate, but increased the activity of pyridoxal kinase in 7 days. This initial elevation in kinase activity returned to normal levels in 2 weeks, became reduced in 3 weeks and then fluctuated back to normal levels in 4 weeks. These results are interpreted to indicate that chronic intake of levodopa results in adaptive alteration in the activity of pyridoxal kinase. This maintains the steady-state concentration of pyridoxal phosphate in order to meet the levodopa-induced enhancement in decarboxylation reaction.