Small-intestinal transfer mechanism of prunasin,the primary metabolite of the cyanogenic glycoside amygdalin

Abstract

1 The small-intestinal transfer of prunasin (D-mandelo nitrile-β-D-glucoside), the primary metabolite of amyg dalin which is not absorbed in the small intestine as such, was studied in rat jejunum and ileum in vitro.

2 As shown by high pressure liquid chromatography, prunasin is transferred essentially intact across the intesti nal wall, without cleavage of the glycosidic bond and thus no formation of benzaldehyde or cyanide during the mucosal passage.

3 Only the jejunal transfer of prunasin followed satura tion kinetics (v_max = 1.6 μmol cm^-1 min^-1; K_T = 460 μmol l^-1) and exhibited a clearsodium-ion dependence. As indicated by the temperature dependence, only the jejunal mucosa- to-serosa transfer and the corresponding tissue uptake of prunasin required apparently high activation energies. Transfer in the terminal ileum showed diffusion character istics.

4 Jejunal methyl α-D-glucoside transfer was inhibited by the presence of prunasin. Furthermore, the tissue uptake of methyl α-D-glucoside in rat jejunum was competitively inhibited by prunasin.

5 The results indicate that prunasin is absorbed unmetabolised in the jejunum of the rat via the transport system of glucose.