Uptake of 3,4‐Dihydroxyphenylalanine and 5‐Hydroxytryptophan by Gatecholamine Forming Mast Cells in the Hamster

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Abstract
The uptake of L‐DOPA, D‐DOPA and 5‐HTP in the CA forming mast cells in the hamster was studied by means of the histochemical fluorescence method of Hillarp and coworkers. It was found that the mast cells of the cheek pouch did not develop any fluorescence even after high doses of L‐DOPA. The mast cells of the ear, on the other hand, which normally show a weak green fluorescence, were able to take up both DOPA and 5‐HTP, but not DA. The amount of precursor taken up and/or decarboxylated by the cells was by far largest after L‐DOPA treatment, but much smaller after D‐DOPA or 5‐HTP administration. Decarboxylase inhibition (NSD‐1015) prevented to a large degree the development of fluorescence after L‐DOPA treatment. MAO‐inhibition did not increase the fluorescence intensity in normal animals, whereas pretreatment with the MAO‐inhibitor nialamide was necessary to give an obvious yellow fluorescence in the mast cell granules after 5‐HTP administration. It is suggested that these mast cells contain a true DOPA decarboxylase with a certain stereospecificity for the L‐isomer. The presence of a weak MAO‐activity in the cells is also discussed.