Neurogenic and non-neurogenic mechanisms in response of rat distal colon muscle to dextran sulphate sodium treatment

Constitutive expression of inducible nitric oxide synthase in healthy rat urothelium?

BACKGROUND

Contrasting findings have been reported regarding a possible constitutive expression of inducible nitric oxide synthase (iNOS) in a normal mammalian bladder. The current study was designed to further investigate such putative iNOS expression.

MATERIALS AND METHODS

The experiments were conducted with paraffin-embedded archival material from the urinary bladder of 6 normal, male Sprague-Dawley rats. In addition, two normal female mice (C57BL/6) were sacrificed and the urinary bladders were harvested. The occurrence of iNOS mRNA was examined by the RNAScope in situ hybridization method. Protein expression of iNOS and 3-nitrotyrosine (the latter used as an indicator of oxidative stress) was investigated by immunohistochemistry.

RESULTS

No expression of iNOS mRNA was observed in the bladder tissue. iNOS protein and 3-nitrotyrosine were strongly expressed in the urothelium. iNOS was also expressed perinuclearly in the detrusor.

CONCLUSIONS

Although the RNAScope methodology could not demonstrate mRNA for iNOS in the normal urinary bladder, the results by immunohistochemistry strongly suggest the occurrence of iNOS in particular, in the urothelium. Positive reactivity for 3-nitrotyrosine may indicate ongoing oxidative stress of the urothelium. The finding of perinuclear iNOS immunoreactivity could suggest an intracrine signaling function by iNOS to the nucleus.

Nicotine-induced neurogenic relaxation in the mouse colon: changes with dextran sodium sulfate-induced colitis

Nicotine has been shown to reduce both tone and muscular activity in the human colon by releasing nitric oxide (NO) from nerves. To our knowledge, however, the effect of nicotine on mouse colon has not been elucidated, and the response in tissue from ulcerative colitis (UC) has not been investigated. We examined nicotine-induced responses in colon from control mice and mice with dextran sodium sulfate (DSS)-induced UC. In controls, bath application of nicotine caused a transient relaxation in longitudinal preparations from the transverse and distal colons but not from the rectum. The response was observed in the presence of bethanechol, abolished by treatment with tetrodotoxin and hexamethonium, and mediated partially (>50%) by the NO pathway. In longitudinal preparations of the distal colon from DSS-treated mice, spontaneous contractions decreased markedly, and nicotine caused contraction without relaxation in half of the preparations tested. Nicotine-induced relaxation in the presence of bethanechol was significantly decreased in the DSS-treated distal colon without changing bethanechol-induced contractions. These data suggest that 1) responses to nicotine differ dependent on colon regions, 2) DSS treatment predominantly caused nicotine-sensitive neurogenic changes in distal colon, and 3) DSS treatment may reverse the direction of nicotine-evoked responses in the colon, in mice.

Influence of soluble guanylate cyclase inhibition on inflammation and motility disturbances in DSS-induced colitis

Nitric oxide (NO) has been associated with a spectrum of harmful to protective roles in inflammatory bowel disease. The involvement of soluble guanylate cyclase (sGC)--the downstream effector of NO--in the negative effect of NO in inflammatory models has been proposed but this has not been evaluated in inflammatory bowel diseases. The present study investigates therefore the influence of colonic inflammation on sGC activity, as well as the effect of in vivo sGC inhibition on colonic inflammation and on in vitro changes in colonic motility in the dextran sulfate sodium (DSS)-model of colitis in rat. Administration of 7% DSS in the drinking water for 6 days resulted in colonic inflammation as judged from histology and myeloperoxidase activity, accompanied by weight loss and bloody stools. Plasma and colonic tissue cyclic guanosine 3',5'-monophosphate (cGMP) levels were decreased in DSS-treated rats. Colonic levels of neuronal NO synthase (nNOS) mRNA and immunoreactivity were not influenced, while those of inducible NO synthase (iNOS) and colonic nitrite/nitrate levels were increased by DSS exposure. Circular muscle strips from inflamed distal colon showed decreased inhibitory responses towards electrical field stimulation and exogenous NO, while methacholine-induced phasic activity was suppressed. Inhibition of sGC by in vivo treatment with ODQ further reduced cGMP levels but did not prevent the inflammation and motility alterations. These results suggest that DSS-induced colitis in rats is accompanied by a reduced sensitivity of sGC, leading to reduced basal cGMP levels and decreased colonic responsiveness towards nitrergic stimuli, but pharmacological reduction of cGMP generation does not prevent the development of DSS-induced colitis.

NOS isoenzyme content in brain nuclei as related to food intake in experimental cancer cachexia

Evidence implies that nitric oxide (NO) in the central nervous systems mediates anorexia in tumor-bearing hosts. We have therefore evaluated, by immunohistochemical image analyses, net alterations of nitric oxide synthases (nNOS, eNOS, iNOS) in brain nuclei [paraventricular hypothalamic nucleus (PVN), medial habenular nucleus (MHB), lateral habenular nucleus (LHB), paraventricular thalamic nucleus (PV), lateral hypothalamic area (LHA), ventromedial hypothalamic nucleus (VMH), nucleus of the solitary tract (NTS)] of tumor-bearing mice (TB) with prostanoid-related anorexia. Pair-fed (PF) and freely fed (FF) non-tumor-bearing mice were used as controls. c-fos was analyzed as indicator of neuronal activation. nNOS was significantly increased in VMH and PVN from TB mice, while eNOS was significantly increased in LHB and LHA. iNOS was significantly increased in LHA and PVN nuclei, but decreased in MHB, LHB and VMH from tumor-bearers. However, several of these alterations were similarly observed in brain nuclei from pair-fed controls. Provision of unspecific NOS-antagonists to TB mice increased nNOS, eNOS and iNOS in several brain nuclei (PVN, LHA, VMH), but left tumor-induced anorexia unchanged. c-fos was significantly increased in all brain nuclei in PF mice except for NTS, LHA and PVN compared to controls, while tumor-bearing mice had increased c-fos in LHA and PVN only compared to controls. Our results demonstrate a complex picture of NOS expression in brain areas of relevance for appetite in tumor-bearing hosts, where most changes seemed to be secondary to stress during negative energy balance. By contrast, NOS content in PVN and LHA nuclei remains candidate behind anorexia in tumor disease. However, nitric oxide does not seem to be a primary mediator behind tumor-induced anorexia. NO may rather secondarily support energy intake in conditions with negative energy balance.