VIP and gastroesophageal reflux disease: Kassim et al [15] found that serum nitrate and VIP levels were significantly higher in GERD patients than the control group (P < 0.001), and there was a significant positive correlation between the grade of lower end esophagitis and each of serum nitrate and VIP (P < 0.001), as well as between serum nitrate and each of serum VIP, suggesting that abnormal levels of serum VIP and NO may have a role in the pathogenesis of GERD.