Intestinal nitric oxide output during reduced mucosal blood flow in healthy volunteers

Relaxant effect of chloroquine in rat ileum: possible involvement of nitric oxide and BKCa

Objectives

Bitter perception has a particularly important role in host defence. However, to date, direct effects of bitter compounds on small intestinal motility have not been shown. This study investigated the effects of bitter compounds on the spontaneous contraction of longitudinal smooth muscle strips of rat ileum.

Methods

Isolated longitudinal smooth muscle strips of rat ileum were used for tension recording in vitro. Immunofluorescence staining was used to identify the localization of TAS2R10 receptors.

Key findings

The spontaneous contraction of rat ileum was decreased after chloroquine administration. Other bitter compounds, such as quinine, denatonium and saccharin, exhibited similar effects. Chloroquine-induced relaxation was not blocked by tetrodotoxin, but was partially reversed by the nitric oxide synthase inhibitor L-NAME or the large conductance Ca2+-activated K+ (BKCa) channel antagonist iberiotoxin. By surgically removing the small intestinal mucosa or bathing in Ca2+-free Krebs solution, the chloroquine-induced relaxation was largely attenuated. The immunofluorescence staining showed that TAS2R10 receptors were expressed in rat ileum.

Conclusions

The results indicate that bitter receptor agonists induce relaxation of longitudinal smooth muscle strips of rat ileum, which is mediated by nitric oxide and BKCa channels.

Review article: the pathophysiological roles of the renin-angiotensin system in the gastrointestinal tract

BACKGROUND

The renin-angiotensin system (RAS) is a homeostatic pathway widely known to regulate cardiovascular and renal physiology; however, little is known about its influence in gastrointestinal tissues.

AIM

To elicit the anatomical distribution and physiological significance of the components of the RAS in the gastrointestinal tract.

METHODS

An extensive online literature review including Pubmed and Medline.

RESULTS

There is evidence for RAS involvement in gastrointestinal physiology and pathophysiology, with all the components required for autonomous regulation identified throughout the gastrointestinal tract. The RAS is implicated in the regulation of glucose, amino acid, fluid and electrolyte absorption and secretion, motility, inflammation, blood flow and possibly malignant disease within the gastrointestinal tract. Animal studies investigating the effects of RAS blockade in a range of conditions including inflammatory bowel disease, functional gut disorders, gastrointestinal malignancy and even intestinal ischaemia have been encouraging to date. Given the ready availability of drugs that modify the RAS and their excellent safety profile, an opportunity exists for investigation of their possible therapeutic role in a variety of human gastrointestinal diseases.

CONCLUSIONS

The gastrointestinal renin-angiotensin system appears to be intricately involved in a number of physiological processes, and provides a possible target for novel investigative and therapeutic approaches.

The angiotensin II type 2 receptor and the gastrointestinal tract

The renin-angiotensin system (RAS) is well known for its vital involvement in body fluid homeostasis and circulation. However, very little research has been devoted to the impact of this regulatory system on the gastrointestinal (GI) system. This is surprising because the GI tract is fundamental for the intake and excretion of fluid and electrolytes (and nutrients), and it accommodates a large proportion of bodily haemodynamics and host defence systems. The RAS is well expressed and active in the GI tract, although the exact roles for the key mediator angiotensin II (Ang II) and its receptors in general, and the type 2 (AT 2) receptor in particular, are not completely settled. There are several reports showing Ang II regulation of intestinal fluid and electrolyte transport. For example, mucosaprotective duodenal bicarbonate-rich secretion is inhibited by Ang II via type 1 (AT1) receptor-mediated facilitation of sympathoadrenergic activity, but this secretory process can also be stimulated by Ang II via AT2 receptors. Novel data from human oesophagus and jejunum suggest that the AT1 receptor mediates muscular contractions and that the AT2 receptor regulates epithelial functions. Data are accumulating suggesting involvement of AT1 and AT2 receptors in GI inflammation and carcinogenesis. The picture of the RAS and AT 2 receptor in the GI tract is, however, far from complete. Much more basic research is needed with regard to GI pathophysiology before concluding clinical significance and potential applicability of pharmacological interferences with the RAS.

A method to attenuate pneumoperitoneum-induced reductions in splanchnic blood flow

OBJECTIVE

To determine if increasing nitric oxide bioactivity by inclusion of ethyl nitrite (ENO) in the insufflation admixture would attenuate pneumoperitoneum-induced decreases in splanchnic perfusion.

SUMMARY BACKGROUND DATA

Organ blood flow is reduced during pneumoperitoneum and can contribute to laparoscopy-associated morbidity and mortality. Previous attempts to control such decreases in flow have been ineffective.

METHODS

Laser-Doppler flow probes were placed on the liver and right kidney of anesthetized pigs. After a baseline recording period, animals were insufflated to a final intraperitoneal pressure of 15 mm Hg. Group one received CO2 (standard practice), whereas group 2 received CO2 plus 100 ppm ENO. Insufflation was maintained for 60 minutes and then the abdomen was manually deflated; monitoring was continued for another 60 minutes.

RESULTS

CO2 insufflation (n = 5) cut liver blood flow in half; liver flow remained at this level throughout the postinsufflation period. Inclusion of 100 ppm ENO (n = 6) attenuated both the acute and prolonged blood flow decreases. Statistical modeling of the data showed that, on average, liver blood flow was 14.3 U/min higher in the ENO pigs compared with the CO2 group (P = 0.0454). In contrast, neither treatment significantly altered kidney blood flow (P = 0.6215).

CONCLUSION

The data indicate that ENO can effectively attenuate pneumoperitoneum-induced blood flow decreases within the peritoneal cavity. The result suggests a novel therapeutic method of regulating hemodynamic changes during laparoscopic procedures.

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