The uptake and metabolism of l-3,4-dihydroxyphenylalanine (dopa) in different rat tissues were studied after the administration of a single parenteral dose of l-dopa. The glandular portion of the rat stomach concentrated dopa in excess of plasma (6-fold), while cardiac dopa levels remained at or below the corresponding plasma level. The accumulation of dopa during the first 30 min after i.v. l-dopa was significantly greater in the glandular stomach than in the heart, duodenum, ileum or non-glandular stomach. The duodenum and ileum synthesized significantly more dopamine (DA) from dopa than did the other tissues. Studies with 3H-l-dopa revealed that the duodenum and ileum formed the most 3H-O-methylated metabolites. The total accumulation of tritium after 3H-l-dopa was greatest in the duodenum. Dopa and DA were localized to the cytosol in both glandular stomach and duodenum. Dopa and DA stores in the stomach were resistant to reserpine; 6-hydroxydopamine (6-OHDA) partially inhibited dopa and DA accumulation in glandular stomach but not in heart. It is concluded that the uptake and metabolism of dopa in different organs are heterogenous. The tissues of the gastrointestinal tract, in particular, are capable of taking up, metabolizing and storing dopa and dopa metabolites in high concentration. The uptake and metabolism of dopa are largely outside the adrenergic nerves.
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