Synthesis of nitric oxide in post‐ganglionic myenteric neurons during endotoxemia: implications for gastric motor function

Abstract

We have investigated the mechanisms underlying acute changes in gastric motor function triggered by endotoxemia. In fundal strips from rats pre-treated with endotoxin (40 microg/kg, i.p. 30 min), mechanical activity was analyzed and the source of nitric oxide (NO) was visualized by confocal microscopy of tissue loaded with the fluorescent dye DAF-FM. NOS expression was determined by quantitative RT-PCR and Western blot, and enzyme activity by the citrulline assay. Strips from endotoxin-treated rats were hypo-contractile. This was prevented by pre-incubation with the neurotoxin tetrodotoxin, the gangliar blocker hexamethonium, or non-selective and neuronal-specific NOS inhibitors (L-NOARG and TRIM, respectively). The soluble guanylyl cyclase (sGC) inhibitor ODQ and the inhibitor of small conductance Ca2+-activated K+ channels apamin prevented relaxation induced by endotoxin, nicotine, exogenous NO (DETA-NONOate), and the NO-independent sGC activator BAY 41-2272. NO synthesis was observed in neuronal soma, axons, and nerve endings of the myenteric plexus in the fundus of endotoxin-treated rats and was prevented by L-NAME, tetrodotoxin, and hexamethonium. nNOS and iNOS mRNA and protein contents were unchanged. Our findings demonstrate synthesis of NO in post-ganglionic myenteric neurons during early endotoxemia that mediates gastric hypo-contractility. The effect of NO is mediated via sGC and small conductance Ca2+-activated K+channels.

Urocortins and CRF type 2 receptor isoforms expression in the rat stomach are regulated by endotoxin: role in the modulation of delayed gastric emptying

“…These data are indicative that activation of CRF 2 receptors by Ucns plays a role in restraining the inhibitory action of LPS on gastric emptying. This may be mediated by counteracting inflammatory mediators shown to underlie LPSinduced inhibition of gastric emptying, namely the increase in TNF-␣-nitric oxide production (29,51). In support of this assertion, several in vivo and in vitro studies indicate that Ucns exert a CRF 2 -mediated attenuation of the early phase of LPSinduced inflammatory response by inhibiting TNF-␣ and interleukin-1 release (1,59,60,66).…”

Nitric oxide, derived from inducible nitric oxide synthase, decreases hypoxia inducible factor‐1α in macrophages during aspirin‐induced mesenteric inflammation

“…NO synthesis was visualized with the cell permeable fluorescent precursor, 4-amino-5-methylamino-2′,7′-difluorofluorescein (DAF-FM) diacetate as previously reported (Quintana et al, 2004). Inside cells, this is hydrolysed by cytosolic esterases to the non-permeable DAF-FM.…”

Effects of occupational stress on the gastrointestinal tract

“…Two variables related to GIT motility are particularly important: (1) peristalsis, which is a function of the frequency and magnitude of the gastric contractions that are generated by the pacemaker area and (2) gastric emptying, which is a measure of the average time the stomach takes to empty half of its luminal content. The ANS regulates GIT motility, controlling peristaltic activity through the myenteric system [59,60] (Figure 1). In fact, alterations in GIT motility are frequently viewed as signs of neuropathy of the myenteric plexus or other pathologies of neuropathic origin.…”