The metabolic interconversion of arecoline and arecoline 1-oxide in the rat.

1. Tritiation of arecoline hydrochloride by catalytic exchange in aqueous media (done by The Radiochemical Centre) gave arecaidine hydrochloride of high specific radioactivity; this on treatment with diazomethane gave [(3)H]arecoline, which was oxidized with peroxyacetic acid to [(3)H]arecoline 1-oxide. 2. Arecoline 1-oxide gave arecaidine 1-oxide on acid hydrolysis and 1,2-dihydro-1-methylnicotinic acid methyl ester on thermal decomposition. 3. [(3)H]Arecoline hydrochloride was metabolized in the rat into the (3)H-labelled derivatives of arecoline 1-oxide, arecaidine 1-oxide, arecaidine, N-acetyl-S-(3-carboxy-1-methylpiperid-4-yl)-l-cysteine and an unidentified metabolite; some unchanged arecoline was also excreted. [(3)H]Arecoline 1-oxide gave the same metabolities, but in different amounts. 4. The possible relevance of these findings to betel-nut carcinogenesis is discussed.