Stimulation of the nitric oxide-guanosine 3', 5'-cyclic monophosphate pathway by sildenafil: effect on rectal muscle tone, distensibility, and perception in health and in irritable bowel syndrome.
Fritz E, Hammer J, Schmidt B, Eherer AJ, Hammer HF.
Am J Gastroenterol. 2003 Oct;98(10):2253-60. doi: 10.1111/j.1572-0241.2003.07661.x.