Adverse reactions to synthetic food colours: interactions between tartrazine and muscarinic acetylcholine receptors in isolated guinea-pig ileum.

The ability of selected food colours to interact with isolated guinea-pig ileum was investigated using a gut bath system. Studies revealed that guinea-pig ileum was specifically sensitive to tartrazine. Intestinal contraction occurred dose-dependently down to a minimum effective dose of 10 microM. All other colours examined proved negative. Studies investigating the biological activity of structural analogues of tartrazine revealed the ability to initiate intestinal contraction was associated with the presence of the carboxylic acid residue at the R1 position of the pyrazole ring. Blocking studies showed that tartrazine contraction was inhibited by atropine alone but not by any other blocking agent tested, implying that tartrazine acts either directly or indirectly upon the muscarinic acetylcholine receptor associated with parasympathetic innervation.