Ileocecal sphincter contraction to colonic distension: A tachykinin-mediated spinal reflex

The ileocecal sphincter in the cat demonstrates a reflex contraction to colonic distension. This study investigates the pathway mediating this reflex in the intact bowel using an in vivo model. The ileocecal sphincter (ICS) and distal ileal intraluminal pressures were recorded in fasted chloralose-anesthetized cats. Colonic balloon distension caused a slight, but significant, ileal inhibition with a maximum decrease from resting ileal pressure by 2.6 ± 0.76 mmHg (P < 0.005) to 3 ml distension. A volume-dependent contraction at the ICS was seen with a maximal contraction of 16.8 ± 2.2 mmHg (P < 0.005) with 4 ml distension. The reflex ICS contraction was inhibited by tetrodotoxin and phentolamine but not by bilateral cervical vagotomy, naloxone, atropine, or trimethaphan camsylate. The reflex contraction at the ICS was inhibited by substance P tachyphylaxis. Substance P tachyphylaxis did not inhibit ICS contraction to phenylephrine. The substance P antagonist, [DArg¹,DTrp^7,9,Leu¹¹]substance P failed to antagonize substance P and failed to inhibit the ICS contractile response to colonic balloon distension. Spinal anesthesia inhibited this reflex. We have thus demonstrated that the ICS reflex contraction to colonic balloon distension in the intact bowel is mediated by an extrinsic spinal neural pathway involving both tachykinin and catecholamines as neurotransmitters.