THE ROLE OF INCREASED NITRIC-OXIDE IN THE VASCULAR HYPOREACTIVITY TO NORADRENALINE IN LONG-TERM PORTAL-VEIN LIGATED RATS

To test the possible role of nitric oxide production in long-term portal vein ligation in the rat, where the hyperdynamic circulation was reported to be absent, in vivo experiments on isolated thoracic aortic rings from partial portal vein ligated or sham-operated rats were performed, 6 months postoperatively. The concentration-response curves to noradrenaline of both intact and endothelium-denuded rings from portal hypertensive rats were significantly shifted to the right as compared to those from sham-operated animals. In intact rings, addition of NG-nitro-L-arginine, a specific inhibitor of nitric oxide synthase, resulted in a significant shift of the curves to the left in sham-operated and portal vein ligated rats. In endothelium-denuded rings, addition of NG-nitro-L-arginine resulted in a significant shift of the curves to the left in portal vein ligated but not in sham-operated animals. After blockade of the nitric oxide biosynthesis with NG-nitro-L-arginine, the negative logarithm of the concentration of nonadrenaline causing half-maximal response did not significantly differ any more between portal vein ligated and sham-operated rats; in endothelium-denuded rings hyporeactivity to noradrenaline persisted in portal vein ligated rats. Only in the intact rings did NG-nitro-L-arginine significantly increase the maximal contractions. No differences were demonstrated in endothelium-dependent relaxations to acetylcholine between sham-operated and portal hypertensive animals. From these results, it can be concluded that in vitro aortic hyporeactivity to noradrenaline is still present in long-term portal vein ligated rats, and that it results at least partially from activation of the L-arginine: nitric oxide pathway in the aortic vascular wal

Aminoguanidine reverses aortic hyporeactivity to noradrenaline in portal vein-ligated rats

To evaluate the role of the inducible and endothelial constitutive nitric oxide synthase in vascular hyporeactivity to vasopressors in portal hypertension, in vitro experiments were performed on intact and endothelium-denuded isolated thoracic aortic rings from portal vein-ligated and sham-operated rats in control conditions, in the presence of aminoguanidine alone, considered to be a selective inhibitor of the inducible nitric oxide synthase, and of aminoguanidine and the nonselective nitric oxide synthase inhibitor N(G)-nitro-L-arginine. In control conditions, hyporeactivity to noradrenaline was observed in both rings with and without endothelium from portal hypertensive versus sham-operated rats. In the rings with endothelium, aminoguanidine reverted this hyporeactivity in portal hypertensive rats. N(G)-Nitro-L-arginine caused an additional shift to the left of the concentration-response curves to noradrenaline in portal hypertensive and a similar shift in sham-operated rats. In the endothelium-denuded rings, aminoguanidine caused no significant changes in portal hypertensive rats, whereas a significant shift to the right in the sham-operated rats was noted, however similar as the shift in the time controls not preincubated with aminoguanidine. No significant further changes were observed after preincubation with the two inhibitors. The endothelium-dependent relaxations to acetylcholine were attenuated in portal hypertensive versus sham-operated rats; addition of aminoguanidine shifted the relaxation curves to the left in portal hypertensive but not in sham-operated rats. These results provide indirect evidence for an increased activity of the inducible nitric oxide synthase in the intact aortic rings but not in the endothelium-denuded rings from portal vein-ligated rats, where other factors seem to be responsible for the observed hyporeactivity to noradrenaline. The endothelial constitutive nitric oxide synthase in rings from portal vein-ligated rats shows a reduced activity which is alleviated after inhibition of the inducible enzyme by aminoguanidin

FUNCTIONAL STUDY ON THE ROLE OF TACHYKININS IN COLONIC PERISTALTIC ACTIVITY IN MICE

Because the role of tachykinin receptors in colonic peristalsis remains incompletely understood, we studied the effect of tachykinin receptor antagonists on mouse colonic peristaltic activity. Peristaltic activity was assessed by quantifying the amplitude and interval of distension-induced pressure waves in proximal and distal colon segments of mice using a modified Trendelenburg set-up. We studied the effect of the NK1, NK2 and NK3 tachykinin receptor antagonists RP67580 (2 mM), nepadutant (1 mM) and SR142801 (0.3 mM) respectively. Gradual distension of proximal and distal colon segments induced repetitive rhythmic pressure waves which were blocked by tetrodotoxin (1 mM) and virtually abolished by hexamethonium (0.1 mM) demonstrating their neuronal origin. The NK1 receptor blocker RP67580 significantly reduced the amplitude of the pressure waves in segments of proximal (5.90.7 to 1.80.8 cmH2O, n=7) and distal (4.80.6 to 1.50.7 cmH2O, n=6) colon. RP67580 significantly reduced the interval in the proximal (667 to 876 s, n=5) but not in the distal colon. The NK2 receptor blocker nepadutant significantly reduced the amplitude (5.20.5 to 3.30.7 cmH2O, n=7) and the interval (527 to 396 s, n=7) in the proximal colon without affecting peristaltic parameters in the distal colon. Blockade of NK3 receptors by SR142801 did not affect the amplitude or interval of peristaltic waves in the proximal and distal colon. Combined blockade of NK1, NK2 plus NK3 receptors significantly reduced the amplitude in the proximal colon (6.50.9 to 1.60.8 cmH2O, n=6) and prolonged the interval (635 to 10622 s, n=6). Our study shows that mouse colonic peristaltic activity has a strong tachykininergic component that is mediated mainly by NK1 receptors and to a lesser extent by NK2 receptors. We could not demonstrate a role for NK3 receptors

Effect of cannabidiol on sepsis-induced motility disturbances in mice: involvement of CB(1) receptors and fatty acid amide hydrolase

Sepsis is an inflammatory condition that is associated with reduced propulsive gastrointestinal motility (ileus). A therapeutic option to treat sepsis is to promote intestinal propulsion preventing bacterial stasis, overgrowth and translocation. Recent evidence suggests that anti-oxidants improve sepsis-induced ileus. Cannabidiol, a non-psychotropic component of Cannabis sativa, exerts strong anti-oxidant and anti-inflammatory effects without binding to cannabinoid CB(1) or CB(2) receptors. Cannabidiol also regulates the activity of fatty acid amide hydrolase (FAAH) which is the main enzyme involved in endocannabinoid breakdown and which modulates gastrointestinal motility. Because of the therapeutic potential of cannabidiol in several pathologies, we investigated its effect on sepsis-induced ileus and on cannabinoid receptor and FAAH expression in the mouse intestine. Sepsis was induced by treating mice with lipopolysaccharides for 18 h. Sepsis led to a decrease in gastric emptying and intestinal transit. Cannabidiol further reduced gastrointestinal motility in septic mice but did not affect gastrointestinal motility in control mice. A low concentration of the CB(1) antagonist AM251 did not affect gastrointestinal motility in control mice but reversed the effect of cannabidiol in septic mice. Sepsis was associated with a selective upregulation of intestinal CB(1) receptors without affecting CB(2) receptor expression and with increased FAAH expression. The increase in FAAH expression was completely reversed by cannabidiol but not affected by AM251. Our results show that sepsis leads to an imbalance of the endocannabinoid system in the mouse intestine. Despite its proven anti-oxidant and anti-inflammatory properties, cannabidiol may be of limited use for the treatment of sepsis-induced ileus