Effects of substrates for aromatic L-amino acid decarboxylase on insulin secretion

It has been shown that substrates for aromatic L-amino acid decarboxylase potentiate glucose-induced insulin release. Microdissected islets of obese-hyperglycemic mice (Umeå ob/ob) have now been used in a study of the effects of decarboxylase substrates on insulin release induced by secretagogues other than glucose. L-5-hydroxytryptophan (L-5-HTP) at 4 mmol/l potentiated the effect of 1 mumol/l glibenclamide, 20 mmol/l D,L-glyceraldehyde or 20 mmol/l K+, but not that of 50 mumol/l chloromercuribenzene-p-sulphonic acid. The potentiating effect of 4 mmol/l L-5-HTP, 4 mmol/l D,L-m-tyrosine, or 4 mmol/l D,L-o-tyrosine on insulin release induced by 20 mmol/l L-leucine was inhibited by 0.1 mmol/l benserazide. Benserazide did not reduce the effect of 10 mmol/l L-glutamine on L-leucine-induced insulin release. L-dihydroxyphenylalanine inhibited glucose-induced insulin secretion at 0.1 mmol/l with a tendency towards a reduction also at lower concentrations. The findings support the hypothesis that increased activity of aromatic L-amino acid decarboxylase can stimulate islet B cell function.