ESR1 and irritable bowel syndrome: On the other hand, the pro-nociceptive action occurs because of the enhancement of serotonin secretion in the intestinal mucosal mast cells (IMMCs); cells in which estrogen receptors have been found and that have been associated with its degranulation, increasing the visceral motor response and spinal or supraspinal processing of visceral nociception, mainly in IBS [9].