Smooth muscle cells distributed in the visceral organs are under the control of the autonomic nervous system, and contraction or relaxation of the muscle cells plays an important physiological role in the control of blood pressure, motility of the digestive, respiratory and urinary tracts and secretion.
Recent physiological, pharmacological and histochemical investigations indicate that neurotransmitters other than acetylcholine or noradrenaline are involved in peripheral autonomic neuro-effector transmission, and these neurotransmitters are generally termed non-adrenergic, non-cholinergic (NANC) neurotransmitters. The neurotransmitters responsible for excitatory and inhibitory NANC neurotransmission (e-NANC and i-NANC respectively) have not been conclusively identified, but ATP, nitric oxide (NO) and peptides such as VIP and substance P are candidates for these roles. In this review, we discuss the possible role of ATP and NO as e-or i-NANC neurotransmitter in the digestive, respiratory and urinary tracts.
Much of the work on NANC innervation in the digestive tract has been carried out on the circular muscle layers of the ileum. This receives inhibitory NANC innervation with ATP responsible for fast relaxation and VIP, and possibly NO, for the slow response. Early and late excitatory junction potentials can be recorded in the presence of atropine. The second is due to substance P since it is blocked in the presence of spantide and by desensitization of the tissue with high doses of substance P. The transmitter responsible for the early NANC contraction has not been identified.
Electrical field stimulation (EFS) applied to the tracheal smooth muscle during contrac-tion induced by 5-HT in the presence of atropine and guanethidine elicited monophasic NANC relaxation. By contrast, NANC relaxation elicited in the smaller airways was biphasic, comprising an initial fast component followed by a second slow one. L-NAME selectively abolished the first component without affecting the second. VIP-antagonists or α-chymotrypsin considerably attenuated the amplitude of the L-NAME insensitive relaxation. These results indicate that at least two neurotransmitters, possibly NO or NO-containing compounds and VIP, are involved in i-NANC neurotransmission in the airway.
In the urinary bladder a large, transient atropine resistant contraction occurs in response to pelvic nerve stimulation. This is blocked by α, β methylene ATP suggesting that it is due to ATP. There is no evidence of inhibitory innervation. In the urethra contraction is completely blocked by atropine and guanethidine; a rapid NANC relaxation is abolished by drugs that block NO synthesis. Nerves containing peptides supply both urethra and bladder and may also be involved.
These results suggest that all visceral smooth muscles may receive inhibitory NANC innervation involving NO.ATP produces contraction of the urinary bladder but relaxation of the digestive tract. The role of peptides is not yet clear but there is evidence that substance P may be an excitatory transmitter and VIP an inhibitory transmitter in many organs.

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The functional disorder of defecation after low anterior resection (LAR) was studied from the aspect of colonic motility in an experiment with dogs using a strain gage transducer, and the follwing results were obtained:
1) In early phase after LAR, the frequency of the colonic contractile waves increased at the proximal and distal sites of the anastomosis in both subgroups of dogs denervated and innervated of hypogastric and pelvic nerves. The increase was more remarkable at the distal site of the anastomosis. Also, the contractile waves were not propagated asross the anastomosis.
2) After LAR, strong colonic contractions occurred during defecation only at the distal anastomosis. Various patterns of contraction time required for defecation were demonstrated as compared to a single pattern in control dogs.
3) The frequency of the occurrence of colonic contractile waves and the propagation of the contraction tended to be normalized with time after LAR both in denervated and innervated groups, though the recovery was faster in the latter subgroup.
4) The frequency of defecation increased after LAR both in denervated and innervated groups compared to be in the control dogs, though more remarkable in the denervated groups. Although tended to be gradually normalized with time after LAR, the colectomized dogs required a long time for normalization of the frequency of defecation.
These results suggested the significant effect of reduction in reservoir space and disturbed continuity of intramural plexus caused by colectomy. Less severity, however, of functional disorder of defecation and earlier recovery from colonic motility disorder in the subgroup of the dogs innervated of autonomic nerves indicated usefulness of retaining autonomic nerves in colectomy.

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Electrogastrography (EGG) appears to be useful method to evaluate the gastric motility as noninvasive approach. However, it is not known what EGG means. The aim of this study is to make clear the meanings of electrical activity recorded dy EGG for gastric motility. EGG recorded by cutaneous electrodes was compared to gastric electromyogram recorded by serosal electrodes and gastric mechanical activity recorded by straingauge transducer in anesthetized and conscious dogs. EGG recordings were preserved when gastric mechanical activity was not recognized. In digestive state, amplitude of EGG, electromyogram and mechanical activity increased significantly (p<0.01). Significant correlation between amplitude of EGG and amplitude of electromyoram and mechanical activity of antrum were seen (p<0.01). In interdigestive state, amplitude of EGG in phase 3 increased significantly (p<0.05) compared to that in phase 1. Significant correlation between amplitude of EGG and amplitude of electromyogram and mechanical activity were seen in phase 2 (p<0.01). EGG reflected electrical control activity (ECA) and electrical response activity (ERA). EGG recordings showed electromyogram and mechanical activity of gastric antrum. Amplitude of EGG reflected electromyogram and mechanical activity in phase 2 in interdigestive state. EGG waves did not always agree on myoelectrical waves.

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To evaluate intestinal motility after 80% massive distal small bowel resection (MSBR), we continuously monitored interdigestive and postprandial bowel motility using bipolar electrodes and/or contractile strain gage force transducers in conscious beagle dogs before, and at 0-4 weeks and 8-13 months after the surgery. Fasting duodenal migrating myoelectric (or motor) complexes (MMCs) occurred at longer intervals in the short-term after 80% MSBR than in controls, and were simulated in long-term that in controls. MMCs arising from the duodenum were often migrated to the proximal jejunum, the jejunum above the anastomosis, and to the terminal ileum beyond the anastomosis. The velocity of duodenal MMC propagation was slowed in every intestinal segment in the short-term, and had not recovered even long after the operation. The duration of the postprandial period without duodenal MMCs was prolonged significantly in the short-term, and still remained longer in the long-term than in controls. These findings suggest that changes in gut motility after MSBR tend to compensate for the shorter intestine and maintain small bowel absorption early postoperatively, and adaptations of motility would occur over the long-term to increased intestinal absorption.

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