Effect of biliary cirrhosis on neurogenic relaxation of rat gastric fundus and anococcygeus muscle: role of nitric oxide pathway.

BACKGROUND: Cirrhosis, associated with a host of hemodynamic abnormalities, could affect the gastrointestinal (GI) tract motility. On the other hand, the nonadrenergic noncholinergic (NANC) neurotransmission has been shown to play a pivotal role in GI tract motility and has been linked with release of nitric oxide (NO) on electrical stimulation. In this study, we investigated the effect of biliary cirrhosis on the neurogenic relaxation of rat gastric fundus and anococcygeus muscle and also the possible role of nitric oxide system in this manner. METHODS: Isolated gastric fundus and anococcygeus strips of sham-operated and biliary cirrhotic (4 weeks after bile duct ligation) rats were mounted under tension in a standard organ bath. Electrical stimulation was applied to obtain NANC-mediated relaxations in precontracted gastric fundus and anococcygeus muscle. The neurogenic relaxations were examined in the presence of different doses of NO synthase inhibitor, N (w)-Nitro-L-Arginine Methyl Ester (L-NAME). The concentration-dependent relaxant responses to the NO donor sodium nitroprusside were also evaluated. RESULTS: The neurogenic relaxation of both gastric fundus and anococcygeus muscle was significantly (P < 0.001) increased in cirrhotic animals. L-NAME (0.03-1,000 µM) inhibited relaxations in both groups in a dose-dependent manner (P < 0.001), but cirrhotic groups were more resistant to the inhibitory effects of L-NAME (P < 0.01). Sodium nitroprusside-mediated relaxations were similar in two groups. CONCLUSIONS: This study for the first time demonstrated that cirrhosis increases the NO-mediated neurogenic relaxation of both rat gastric fundus and anococcygeus muscle, suggesting a crucial role for the neurogenic NO in the pathophysiology of disturbed GI motility in cirrhosis.

Inhibition by lithium of the nitrergic relaxation of rat anococcygeus muscle.

In the present study, we evaluated the effect of lithium on the nitric oxide (NO)-mediated nonadrenergic noncholinergic (NANC) relaxation of rat anococcygeus muscle. The isolated precontracted (phenylephrine, 7.5 microM) rat anococcygeus muscle were relaxed via electrical field stimulation (5 Hz) in the absence or presence of lithium (0.5, 1, and 5mM) or in tissues excised from ex vivo lithium (600 mg/L in drinking water for 30 days)-treated animals. Effects of the NO synthase (NOS) inhibitor L-NAME (0.03 and 100 microM) or guanylyl cyclase inhibitor ODQ (1 microM) and NO precursor L-arginine (1mM) on relaxations were investigated. Effect of either in vitro (1 and 5mM) or ex vivo lithium treatment on relaxation to the NO donor sodium nitroprusside (SNP; 0.1-1000 microM) was also investigated on phenylephrine-contracted strips. The NANC relaxation was significantly reduced by in vitro (1 and 5mM; up to P<0.01) and ex vivo lithium treatment (P<0.001). L-NAME (100 microM and 1mM) and ODQ (1 and 10 microM) significantly inhibited NANC relaxations in either control or lithium-treated strips. Combination of lithium (0.5mM) with L-NAME (0.03 microM) significantly (P<0.001) reduced the NANC relaxation. Although 1mM l-arginine had no effect on relaxations, it prevented their inhibition by both in vitro (1 and 5mM) and ex vivo lithium of relaxations. SNP produced concentration-dependent relaxation in precontracted rat anococcygeus muscle which was not altered by lithium treatment. Reverse transcription polymerase chain reaction (RT-PCR) revealed a significant increase in the neuronal NOS expression in the anococcygeus muscle of ex vivo lithium-treated animals compared with controls. Our experiments suggested that both ex vivo and in vitro lithium administration attenuated the NO-mediated neurogenic relaxation of isolated rat anococcygeus muscle.

ATP-sensitive potassium channels contribute to the time-dependent alteration in the pentylenetetrazole-induced seizure threshold in diabetic mice.

Although there is evidence that diabetes affects seizure susceptibility, the underlying mechanism has not been completely understood. Several studies also suggest a pivotal role for K(ATP) channels in the seizure modulation. The aim of the present study was to evaluate the seizure threshold induced by pentylenetetrazole in diabetic mice at different times (3 days, 1-8 weeks) after induction of diabetes with streptozocin and to examine the possible role of ATP-sensitive potassium (K(ATP)) channels in this manner. Our data showed a time-dependent alteration in the threshold in diabetic mice, reaching a peak on week 2 after streptozocin injection and declining significantly afterwards. The seizure threshold in 8-week diabetic mice was even lower than control levels, though the difference was not significant. The K(ATP) channel opener cromakalim (0.1-30microg/kg, i.p.) significantly increased the seizure threshold in control mice. Although the K(ATP) channel blocker glibenclamide (0.5, 1mg/kg) had no effect, it prevented the effects of the potent dose of cromakalim (30microg/kg) on seizure threshold in control mice. Glibenclamide (1mg/kg, i.p.) also decreased the seizure threshold in 2-week diabetic mice to the control levels which was blocked by pre-treatment with cromakalim (10microg/kg, i.p.). Cromakalim (10microg/kg, i.p.) significantly increased the seizure threshold in 8-week diabetic mice which was inhibited by pre-treatment with glibenclamide (1mg/kg, i.p.). We demonstrated a time-dependent alteration in the pentylenetetrazole-induced seizure threshold in diabetic mice. This phenomenon might be due to the probable alteration in the K(ATP) channel functioning during the diabetic condition.

Nitric oxide involvement in the effect of acute lithium administration on the nonadrenergic noncholinergic-mediated relaxation of rat gastric fundus.

INTRODUCTION: Lithium has largely met its initial promise as the first drug to be discovered in the modern era of psychopharmacology. However, the mechanism for its action remains an enigma. The aim of the present study was to verify the effect of acute lithium administration on the nonadrenergic noncholinergic (NANC)-mediated relaxation of rat isolated gastric fundus and to evaluate the role of nitric oxide pathway in this manner. MATERIALS AND METHODS: The isolated rat gastric fundus strips were precontracted with 0.5 microM serotonin and electrical field stimulation (EFS) was applied at 5 Hz frequency to obtain NANC-mediated relaxation in the presence or absence of lithium (0.1, 0.5, 1 and 5 mM). Also, effects of combining lithium (0.1 mM) with the NO synthase (NOS) inhibitor L-NAME (0.03 microM) or the guanylyl cyclase inhibitor ODQ (1 microM) on relaxant responses to EFS was investigated. Moreover, effects of combining lithium (1 mM) with 0.1 mM L-arginine (a precursor of NO) on neurogenic relaxation were assessed. Also, the effect of lithium (1 mM) on relaxation to sodium nitroprusside (SNP; 1 nM-0.1 mM) and glyceryltrinitrate (GTN; 0.1-10 microM) was investigated. RESULTS: The NANC-mediated relaxation was significantly (P<0.001) reduced by lithium in a dose- and time-dependent manner. Combination of lithium (0.1 mM) with L-NAME (0.03 microM), which separately had partial inhibitory effect on relaxations, significantly (P<0.001) reduced the NANC-mediated relaxation of gastric fundus. ODQ (1 microM) significantly inhibited the neurogenic relaxations in the presence or absence of lithium (0.1 and 1 mM). Although L-arginine at 0.1 mM had no effect on relaxation to EFS, it prevented the inhibition by lithium (1 mM) of relaxant responses to EFS. Also, SNP and GTN produced concentration-dependent relaxation in precontracted rat gastric fundus which was not altered by lithium incubation (1 mM). DISCUSSION: Our experiments indicated that lithium likely by interfering with L-arginine/NO pathway in nitrergic nerve can result in impairment of NANC-mediated relaxation of rat gastric fundus.