Mechanical stimulation is not responsible for activation of gastrointestinal afferents during ischemia

Abdominal ischemia reflexly excites the cardiovascular system through activation of visceral sympathetic afferents. Although a number of ischemic metabolites are known to stimulate sympathetic afferents, the contribution of mechanical stimulation to activation of afferents during abdominal ischemia remains uncertain. Thus the present study examined the role of changes in motility in activation of gastrointestinal afferents during ischemia. Single-unit activity of C fiber afferents located on the stomach, duodenum, jejunum, or colon was recorded from the right sympathetic chain of anesthetized cats during 15 min of ischemia. Intraluminal pressure, as a reflection of local mechanical activity, was measured by an open catheter placed in the lumen of the gastrointestinal tract. The results show that gastrointestinal motility was mainly inhibited during abdominal ischemia. Changes in intraluminal pressure did not correlate with afferent discharge activity during ischemia (r = -0.32, n = 10). Furthermore, discharge frequency of gastrointestinal afferents during ischemia was not altered significantly by topical application of 100 micrograms/ml of atropine (3.98 +/- 0.62 to 3.83 +/- 0.59 imp/s, n = 12), which profoundly inhibited local gastrointestinal motility. Collectively, these data indicate that gastrointestinal motility changes during abdominal ischemia do not contribute to activation of gastrointestinal sympathetic C fiber afferents.