Effects of L-dopa on putrescine levels in the brain and the liver of the rat.

The pharmacological effects of several amino acid precursors of putative neurotransmitters on putrescine levels in the brain and the liver of the rat were studied. L-dopa increased brain and liver putrescine levels in a dose-dependent manner that reached its maximum effect in 4-6 h. The increase in liver putrescine was associated with a concomitant increase in ornithine decarboxylase activity. L-5-hydroxytryptophan increased liver putrescine but had no effect on brain putrescine levels. D-DOPA and D-5-hydroxytryptophan were both ineffective in altering brain or liver putrescine. The effects of L-DOPA persisted after hypophysectomy and were not associated with changes in tissue levels of S-adenosylmethionine. The repeated administration of L-DOPA for periods of 48 and 96 h resulted in a sustained elevation of putrescine levels in the brain but not in the liver.