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The Effects of Sympathetic and Parasympathetic Denervation On Distal Colon Motility in Conscious Rats
Timothy J. Ridolfi*1, Toku Takahashi2, Lauren Kosinski1, Kirk a. Ludwig1
1Surgery, Medical College of Wisconsin, Milwaukee, WI; 2Surgery, Zablocki VA Medical Center, Milwaukee, WI
Background: It is known that extrinsic autonomic denervation of the colon causes changes in colonic motility and defecation. The extrinsic nervous system is subject to injury during low anterior resection. After low anterior resection, patients are likely to experience defecatory disorders, such as urgency, soiling and diarrhea. However, it is not fully understood how sympathetic and parasympathetic nerves regulate the motility of the distal colon. It is also not known how injury to the sympathetic or parasympathetic nerves affects distal colonic motility. We studied colonic motility in response to the stimulation of sympathetic, hypogastric nerves or the parasympathetic, pelvic nerves in anesthetized rats. We also studied the effects of extrinsic denervation of hypogastric nerves or pelvic nerves on distal colonic motility in conscious rats. Methods: Under isoflurane anesthesia, a strain gauge transducer was implanted on the serosal surface of the distal colon to record the circular muscle contractions in SD rats. Using a dissecting microscope, the right hypogastric nerve or pelvic nerve was isolated and electrical nerve stimulation (5 V, 0.5 msec, 1-10 Hz) was performed. Another group underwent transection of bilateral hypogastric nerves or pelvic nerves. Sham operated rats served as controls. After surgery colonic motility was continuously recorded for three days in a conscious state. Changes in colonic motility were evaluated by calculating the motility index (MI) of 30 min recordings. Results: Electrical stimulation of the pelvic nerve caused colonic contractions, while hypogastric nerve stimulation caused colonic relaxation in a frequency dependent manner. The stimulatory effect of the pelvic nerve stimulation and inhibitory effect of the hypogastric nerve stimulation were antagonized by atropine and propranolol, respectively. At 6 hours postoperatively animals with pelvic nerve transections were found to have a significantly reduced MI (518 +/- 185 gram seconds, n=3), compared to that of sham operated rats (975 +/- 243 gram seconds, n=3, p=0.04). In contrast, MI of colonic motility was significantly increased to 5029 +/- 1954 gram seconds (n=3, p=0.02) in rats who underwent hypogastric nerve transection.Conclusion: It is suggested that the pelvic nerve regulates colonic contractions via muscarinic receptors, while the hypogastric nerve regulates colonic relaxations via beta adrenoceptors in rats. Injury of pelvic nerves results in impaired contractions, while injury of hypogastric nerve results in augmented contractions. Our study may help to further understand the pathophysiology of low anterior resection syndrome.
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