6,7-Dihydroxytetrahydroisoquinoline: uptake and storage by peripheral sympathetic nerve of the rat

6,7-Dihydroxy-1,2,3,4-tetrahydroisoquinoline is a pharmacologically active alkaloid that can be formed by condensation of dopamine with formaldehyde. We used fluorescence microscopy to study in vitro the uptake and storage of this compound by sympathetic nerves of the rat iris. Rats were treated with reserpine or with the methyl ester of alpha-methyl-p-tyrosine in order to deplete the endogenous catecholamine stores. Accumulation of the alkaloid was about onetenth that of norepinephrine. Uptake was completely blocked by 10-(5)M desmethylimipramine. These results offer some explanation for the sympathomimetric properties of the alkaloid. Similar results can be expected for similar tetrahydroisoquinolines that may be formed in vivo from endogenous catecholamines during ingestion of alcoholic beverages.