Auramine-O Potentiates the Duodenal Smooth Muscle Contraction Through Promotion of Cholinergic Signalling Pathway

Auramine-O (AO), a synthetic dye belonging to the diarylmethane group, is extensively used in various industrial applications and is used as food additive. Exposure to AO in humans typically occurs through the ingestion of food products tainted with this synthetic colorant. Therefore, this study aimed to examine the effects of AO on the motor functions of the duodenum—a critical segment of the small intestine responsible for small intestinal motility. To evaluate the effect of AO on duodenal visceral smooth muscle (dVSM) motor activity, ex vivo recordings of duodenal movements were conducted using an isotonic transducer (IT-2245) connected to RMS Polyrite D. Rats exposed to AO showed a significant increase in the amplitude of duodenal contractions as compared to control rats in a dose dependent manner. From the tracings, it can be hypothesised that the potentiation of the contraction of the dVSM by AO might be due to facilitation of the activity of excitatory cholinergic myenteric efferents and/or inhibition of the activity of inhibitory nitrergic and/or adrenergic intrinsic myenteric efferents that innervates the SiVSM. Moreover, to investigate the probable neurocrine mechanisms in AO-induced enhancement of the duodenal visceral smooth muscle (dVSM) contractions, the movement of duodenum was recorded in response to application in combination with AO and cholinergic agonists (Acetylcholine) and antagonists (Atropine) respectively. AO exhibited a synergistic enhancement of duodenal visceral smooth muscle (dVSM) contractions in the presence of acetylcholine (ACh), whereas the AO-induced augmentation of dVSM contraction was significantly counteracted following pre-treatment with atropine, the muscarinic antagonist. In conclusion, it is suggested that AO enhances the motor functions of the SiVSM by augmenting the contractions of the SiVSM through cholinergic signalling pathway. These observations provide new insight into auramine’s pharmacodynamic behaviour and raise critical concerns about its potential to disrupt normal gastrointestinal motility when ingested through contaminated food. Keywords: Auramine-O, motor functions, small intestinal visceral smooth muscle, acetylcholine, atropine, cholinergic signalling pathway.