EFS-induced Contractions Research Articles

Effects of extracts and active components of Rhizoma Coptidis on contraction of circular smooth muscle isolated from guinea pig gastric antrum

To identify the influence of extracts and active components of Rhizoma Coptidis on gastric smooth muscle contractility of guinea pigs, and to explore the potential pharmacological mechanism of Rhizoma Coptidis in "invigorating the stomach" and "impairing the stomach". Observing the effects of the water extract and the alkaloids from Rhizoma Coptidis (at doses ranging from 0.3 to 1,000 microg/L) and other active components such as berberine, palmatine and jatrorrhizine (at doses ranging from 0.3 to 1,000 micromol/L) on the spontaneous and electrical field stimulation (EFS)-induced contractions of antral circular smooth muscle strips from guinea pig stomach via a force transducer in vitro. The water extract or the alkaloids from Rhizoma Coptidis could improve the spontaneous contraction at the low doses, but inhibit the spontaneous contraction at the high doses. Berberine, palmatine and jatrorrhizine also showed the similar effects. Moreover, the water extract and the alkaloids of Rhizoma Coptidis, as well as berberine, palmatine and jatrorrhizine could increase the EFS-induced contraction. Among the three monomers, jatrorrhizine exhibited the most potent effect on EFS-induced contraction. The effects of Rhizoma Coptidis in "invigorating the stomach" or "impairing the stomach" may be related to its effect on gastric smooth muscle contractility. Berberine, palmatine and jatrorrhizine are all effective components of Rhizoma Coptidis affecting the contraction of gastric smooth muscle, among which jatrorrhizine is the most potent agent in promoting the contraction while berberine is the most potent one for inhibiting the contraction.

Inhibition of colonic motility and defecation by RS‐127445 suggests an involvement of the 5‐HT2B receptor in rodent large bowel physiology

5-HT(2B) receptors are localized within the myenteric nervous system, but their functions on motor/sensory neurons are unclear. To explore the role of these receptors, we further characterized the 5-HT(2B) receptor antagonist RS-127445 and studied its effects on peristalsis and defecation. Although reported as a selective 5-HT(2B) receptor antagonist, any interactions of RS-127445 with 5-HT(4) receptors are unknown; this was examined using the recombinant receptor and Biomolecular Interaction Detection technology. Mouse isolated colon was mounted in tissue baths for isometric recording of neuronal contractions evoked by electrical field stimulation (EFS), or under an intraluminal pressure gradient to induce peristalsis; the effects of RS-127445 on EFS-induced and on peristaltic contractions were measured. Faecal output of rats in grid-bottom cages was measured over 3 h following i.p. RS-127445 and separately, validation of the effective doses was achieved by determining the free, unbound fraction of RS-127445 in blood and brain. RS-127445 (up to 1 micromol x L(-1)) did not interact with the 5-HT(4) receptor. RS-127445 (0.001-1 micromol x L(-1)) did not affect EFS-induced contractions of the colon, although at 10 micromol x L(-1) the contractions were reduced (to 36 +/- 8% of control, n= 4). RS-127445 (0.1-10 micromol x L(-1)) concentration-dependently reduced peristaltic frequency (n= 4). RS-127445 (1-30 mg x kg(-1)), dose-dependently reduced faecal output, reaching significance at 10 and 30 mg x kg(-1) (n= 6-11). In blood and brain, >98% of RS-127445 was protein-bound. High-protein binding of RS-127445 indicates that relatively high doses are required for efficacy. The results suggest that 5-HT(2B) receptors tonically regulate colonic motility.

Dexamethasone decreases neuronal nitric oxide release in mesenteric arteries from hypertensive rats through decreased protein kinase C activation

Neuronal NO plays a functional role in many vascular tissues, including MAs (mesenteric arteries). Glucocorticoids alter NO release from endothelium and the CNS (central nervous system), but no results from peripheral innervation have been reported. In the present study we investigated the effects of dexamethasone on EFS (electrical field stimulation)-induced NO release in MAs from WKY (Wistar-Kyoto) rats and SHRs (spontaneously hypertensive rats) and the role of PKC (protein kinase C) in this response. In endothelium-denuded MAs, L-NAME (NG-nitro-L-arginine methyl ester) increased the contractile response to EFS only in segments from SHRs. EFS-induced contraction was reduced by 1 micromol/l dexamethasone in segments from SHRs, but not WKY rats, and this effect was abolished in the presence of dexamethasone. EFS induced a tetrodotoxin-resistant NO release in WKY rat MAs, which remained unchanged by 1 micromol/l dexamethasone. In SHR MAs, dexamethasone decreased basal and EFS-induced neuronal NO release, and this decrease was prevented by the glucocorticoid receptor antagonist mifepristone. Dexamethasone did not affect nNOS [neuronal NOS (NO synthase)] expression in either strain. In SHR MAs, incubation with calphostin C (a non-selective PKC inhibitor), Gö6983 (a classic PKC delta and zeta inhibitor), LY379196 (a PKCbeta inhibitor) or PKCzeta-PI (PKCzeta pseudosubstrate inhibitor) decreased both basal and EFS-induced neuronal NO release. Additionally, PKC activity was reduced by dexamethasone. The PKC inhibitor-induced reduction in NO release was unaffected by dexamethasone. In conclusion, results obtained in the present study indicate that PKC activity positively modulates the neuronal NO release in MAs from SHRs. They also reveal that by PKC inhibition, through activation of glucocorticoid receptors, dexamethasone reduces neuronal NO release in these arteries.

Vardenafil-induced relaxation and cyclic nucleotide levels in normal and obstructed rat urinary bladder

To study the effects of the phosphodiesterase-5 inhibitor, vardenafil, on contraction and cyclic nucleotide levels in isolated detrusor preparations with and without mucosa, from control rats and rats with partial urethral obstruction (PUO) and intact mucosa. Female Sprague-Dawley rats were divided into groups subjected to PUO for 14 days (six), and sham-operated control rats (12). Detrusor preparations were mounted in organ baths and effects of increasing concentrations of vardenafil (1 nm to 100 microm) assessed on carbachol-activated (1 microm) preparations, and on contractions induced by transmural activation of nerves (electrical field stimulation, EFS). Levels of cGMP and cAMP were determined using radioimmunoassays. Vardenafil caused concentration-dependent relaxations of carbachol-contracted detrusor, the mean (sd) of which at 100 microm was 91 (4)% in control and 100% in PUO rats. The -log 50% inhibitory concentration (IC(50)) was 4.41 (0.08) and 4.73 (0.05) (P < 0.01), respectively. Removing the mucosa increased the relaxant effect of vardenafil at 1-10 microm (P < 0.05) although -log IC(50) values were unaffected compared to the control. The cGMP levels ( pmol/mg protein) in control preparations increased from 2.5 (0.6) to 5.0 (0.8), and from 1.4 (0.2) to 7.2 (1.3) in obstructed bladders. In mucosa-denuded preparations the cGMP content increased from 0.6 (0.1) to 1.6 (0.4) in response to vardenafil. In control rats, the levels of cAMP increased from 12.8 (2.5) to 18.9 (0.9) (P < 0.05) after vardenafil. In mucosa-denuded preparations the cAMP levels after vardenafil increased from 16.5 (2.11) to 37.8 (3.4) (P < 0.01). In PUO bladders, the tissue content of cAMP increased from 12.6 (2.4) to 20.6 (3.4) (P < 0.01). Vardenafil concentration-dependently inhibited nerve-induced contractions in all groups studied. At 100 microm 19 (3)% of the control contraction remained, vs 8 (1)% for preparations from obstructed rats, and 11 (4)% in mucosa-denuded preparations. In normal rats, vardenafil relaxed carbachol- and inhibited EFS-induced contractions of detrusor preparations with and without urothelium, and in PUO rats with urothelium. Relaxations were accompanied by increases in both cAMP and cGMP content. It is proposed that vardenafil-induced relaxation of rat detrusor, also in obstructed and mucosa-denuded preparations, is mediated via cAMP.

Involvement of β 3-adrenoceptors in mouse urinary bladder function: Role in detrusor muscle relaxation and micturition reflex

β 3-adrenoceptor activation produces relaxation of human urinary bladder smooth muscle (detrusor). Therefore, β 3-adrenoceptor agonism is being investigated as a new therapeutic strategy for the treatment of overactive bladder. The aim of the current study was to identify the functional presence of β 3-adrenoceptors in mouse isolated urinary bladder using the selective β 3-adrenoceptor agonist CL316,243 and antagonists SR59230A and L748,337. The effects of CL316,243 on basal tone, spontaneous activity and electrical field stimulation (EFS)-induced contractions were investigated using in vitro techniques, while the in vivo effects of intravenously administered CL316,243 on the micturition reflex were investigated using cystometry. CL316,243 decreased basal tone (pEC 50 = 6.4 ± 0.4) as well as spontaneous activity (53 ± 7% at 3 µM) and inhibited EFS-induced contractions (pEC 50 = 7.0 ± 0.2) of the detrusor muscle. The β 3-adrenoceptor antagonist SR59230A (1 µM) significantly inhibited the relaxing effects of CL316,243 on basal tone and neurogenic contractions (pA 2 = 7.0 and 7.2, respectively). Another β 3-adrenoceptor antagonist L748,337 (1-10 µM) significantly blocked the CL316,243-evoked inhibition of neurogenic contractions in a concentration-dependent manner (pK B = 6.8), while the selective β 2-adrenoceptor antagonist ICI118,551(30 nM) had no effect. In anesthetized mice, CL316,243 (0.03 and 0.1 mg/kg, i.v.) significantly increased bladder capacity and threshold pressure without a modification of bladder compliance. Moreover, it induced a significant decrease in the amplitude of both micturition and non-voiding contractions. Based on the current results obtained using the β 3-adrenoceptor agonist CL316,243 (as well as various β-adrenoceptor antagonists), functional β 3-adrenoceptors appear to be present in mouse urinary bladder.

Combination of Alfuzosin and Tadalafil Exerts an Additive Relaxant Effect on Human Detrusor and Prostatic Tissues In Vitro

BackgroundLower urinary tract symptoms (LUTS) suggestive of benign prostatic hyperplasia (BPH) and erectile dysfunction (ED) are highly prevalent in aging men and are strongly linked. Alpha1-blockers such as alfuzosin are effective monotherapies for LUTS. Phosphodiesterase type 5 (PDE5) inhibitors such as tadalafil are the first-line treatment for ED. Both drugs act by two different mechanisms of action on common urogenital target organs and, thus, may have additive effects. ObjectivesWe evaluated in vitro the effects of alfuzosin, tadalafil, and the combination of both on human detrusor and prostatic smooth muscle. Design, setting, and participantsProstatic and bladder tissue were obtained from patients (n=20 and n=17, respectively) undergoing cystoprostatectomy for bladder cancer. MeasurementsIn organ baths, isolated prostatic strips and isolated bladder strips were incubated with vehicle, tadalafil (10−6 M and 10−5 M), alfuzosin (3×10−8 M or 10−6 M and 10−5 M) or a combination. Concentration-response curves (CRCs) to norepinephrine were generated on prostatic strips and detrusor strips precontracted with carbachol. Strips were also submitted to electrical field stimulation (EFS). Results and limitationsWhen alfuzosin and tadalafil were combined, the maximal relaxation to norepinephrine on carbachol-precontracted detrusor strips was significantly increased compared with tadalafil alone, and EFS-induced detrusor contractions were better inhibited compared with each compound alone. Tadalafil significantly inhibited norepinephrine-induced prostatic strip contractions by reducing the maximal effect, whereas alfuzosin shifted the CRC of norepinephrine to the right. Combining both tadalafil and alfuzosin resulted in a greater relaxant effect. Likewise, the combination was more effective at reducing EFS-induced contractions compared with each compound alone. ConclusionsThe combination of alfuzosin and tadalafil exerts an additive effect of inhibiting adrenergic smooth muscle tone of prostatic tissue and EFS-induced detrusor contractions and conversely, of enhancing adrenergic relaxation of detrusor precontracted with carbachol. These experiments provide experimental support for the clinical investigation of the combination of α1-blockers and PDE5 inhibitors in the treatment of LUTS.

W2053 The Impact of Using Different Standardized Meals in the Assessment of Motility of Upper Gastrointestinal Tract

Introduction: Motor functions of the stomach have traditionally been regarded to differ by stomach region. However, to date there have been few studies on the gastric contractility of the human stomach. Objectives: The aim of the present study was therefore to examine the response to acetylcholine and electrical field stimulation (EFS) of the human fundus, corpus and antrum. Methods: Gastric muscles were obtained from 71 patients (44 males, 27 females with an average age of 60.7 yrs; 34 85 yrs) undergoing gastric cancer surgery. Muscle strips (n = 71) were isolated and attached to a fixed mount and to an isometric strain gauge. The muscle strips were studied In Vitro for their contractile responses to acetylcholine (n=25) and electrical field stimulation (EFS, n=46). N-nitro-L-arginine (L-NA), atropine and tetrodotoxin (TTX) were added to assess the nitro oxide-mediated changes and cholinergic neural pathway involved in EFS-induced contractions. Results: Spontaneous contractile activity was observed in muscle strips of stomach regions. In the antrum, acetylcholine induced increase in contraction frequency and peak contraction in dose dependent pattern, but no significant change was noticed in muscle tone. In corpus and fundus, acetylcholine induced dose-dependent increase in peak contraction and muscle tone, but there was no significant change in frequency. The response to EFS also differed by stomach region. EFS produced no significant change in contractile activity in 22 of 46 muscle strips. When EFS evoked frequency-dependent contraction or relaxation in muscle strips, contraction was primarily observed in the muscle strips from the antrum, and relaxation was primarily observed in the muscle strips of the corpus and fundus. The addition of LNA (100 uM) to the muscle bath converted the EFS-induced relaxation to contractions and increased the EFS-induced contractions. EFS-induced contractions were abolished by atropine (1uM) or TTX (1uM). Conclusions: Our study demonstrated that the response to acetylcholine and electrical field stimulation on human gastric fundus and corpus is different with that of human gastric antrum.

W2052 Urocortin Reduces Food Intake via Inhibition of Ghrelin Secretion in Rats

Introduction: Motor functions of the stomach have traditionally been regarded to differ by stomach region. However, to date there have been few studies on the gastric contractility of the human stomach. Objectives: The aim of the present study was therefore to examine the response to acetylcholine and electrical field stimulation (EFS) of the human fundus, corpus and antrum. Methods: Gastric muscles were obtained from 71 patients (44 males, 27 females with an average age of 60.7 yrs; 34 85 yrs) undergoing gastric cancer surgery. Muscle strips (n = 71) were isolated and attached to a fixed mount and to an isometric strain gauge. The muscle strips were studied In Vitro for their contractile responses to acetylcholine (n=25) and electrical field stimulation (EFS, n=46). N-nitro-L-arginine (L-NA), atropine and tetrodotoxin (TTX) were added to assess the nitro oxide-mediated changes and cholinergic neural pathway involved in EFS-induced contractions. Results: Spontaneous contractile activity was observed in muscle strips of stomach regions. In the antrum, acetylcholine induced increase in contraction frequency and peak contraction in dose dependent pattern, but no significant change was noticed in muscle tone. In corpus and fundus, acetylcholine induced dose-dependent increase in peak contraction and muscle tone, but there was no significant change in frequency. The response to EFS also differed by stomach region. EFS produced no significant change in contractile activity in 22 of 46 muscle strips. When EFS evoked frequency-dependent contraction or relaxation in muscle strips, contraction was primarily observed in the muscle strips from the antrum, and relaxation was primarily observed in the muscle strips of the corpus and fundus. The addition of LNA (100 uM) to the muscle bath converted the EFS-induced relaxation to contractions and increased the EFS-induced contractions. EFS-induced contractions were abolished by atropine (1uM) or TTX (1uM). Conclusions: Our study demonstrated that the response to acetylcholine and electrical field stimulation on human gastric fundus and corpus is different with that of human gastric antrum.

W2051 Electroacupuncture (EA) Improves Impaired Gastric Accommodation, Gastric Dysrhythmia and Delayed Gastric Emptying via the Opioid Pathway in Diabetic Rats Induced By Streptozotocin (STZ)

Introduction: Motor functions of the stomach have traditionally been regarded to differ by stomach region. However, to date there have been few studies on the gastric contractility of the human stomach. Objectives: The aim of the present study was therefore to examine the response to acetylcholine and electrical field stimulation (EFS) of the human fundus, corpus and antrum. Methods: Gastric muscles were obtained from 71 patients (44 males, 27 females with an average age of 60.7 yrs; 34 85 yrs) undergoing gastric cancer surgery. Muscle strips (n = 71) were isolated and attached to a fixed mount and to an isometric strain gauge. The muscle strips were studied In Vitro for their contractile responses to acetylcholine (n=25) and electrical field stimulation (EFS, n=46). N-nitro-L-arginine (L-NA), atropine and tetrodotoxin (TTX) were added to assess the nitro oxide-mediated changes and cholinergic neural pathway involved in EFS-induced contractions. Results: Spontaneous contractile activity was observed in muscle strips of stomach regions. In the antrum, acetylcholine induced increase in contraction frequency and peak contraction in dose dependent pattern, but no significant change was noticed in muscle tone. In corpus and fundus, acetylcholine induced dose-dependent increase in peak contraction and muscle tone, but there was no significant change in frequency. The response to EFS also differed by stomach region. EFS produced no significant change in contractile activity in 22 of 46 muscle strips. When EFS evoked frequency-dependent contraction or relaxation in muscle strips, contraction was primarily observed in the muscle strips from the antrum, and relaxation was primarily observed in the muscle strips of the corpus and fundus. The addition of LNA (100 uM) to the muscle bath converted the EFS-induced relaxation to contractions and increased the EFS-induced contractions. EFS-induced contractions were abolished by atropine (1uM) or TTX (1uM). Conclusions: Our study demonstrated that the response to acetylcholine and electrical field stimulation on human gastric fundus and corpus is different with that of human gastric antrum.

W2050 Response to Acetylcholine and Electrical Field Stimulation On Human Gastric Fundus and Corpus Is Different with That of Human Gastric Antrum

Introduction: Motor functions of the stomach have traditionally been regarded to differ by stomach region. However, to date there have been few studies on the gastric contractility of the human stomach. Objectives: The aim of the present study was therefore to examine the response to acetylcholine and electrical field stimulation (EFS) of the human fundus, corpus and antrum. Methods: Gastric muscles were obtained from 71 patients (44 males, 27 females with an average age of 60.7 yrs; 34 85 yrs) undergoing gastric cancer surgery. Muscle strips (n = 71) were isolated and attached to a fixed mount and to an isometric strain gauge. The muscle strips were studied In Vitro for their contractile responses to acetylcholine (n=25) and electrical field stimulation (EFS, n=46). N-nitro-L-arginine (L-NA), atropine and tetrodotoxin (TTX) were added to assess the nitro oxide-mediated changes and cholinergic neural pathway involved in EFS-induced contractions. Results: Spontaneous contractile activity was observed in muscle strips of stomach regions. In the antrum, acetylcholine induced increase in contraction frequency and peak contraction in dose dependent pattern, but no significant change was noticed in muscle tone. In corpus and fundus, acetylcholine induced dose-dependent increase in peak contraction and muscle tone, but there was no significant change in frequency. The response to EFS also differed by stomach region. EFS produced no significant change in contractile activity in 22 of 46 muscle strips. When EFS evoked frequency-dependent contraction or relaxation in muscle strips, contraction was primarily observed in the muscle strips from the antrum, and relaxation was primarily observed in the muscle strips of the corpus and fundus. The addition of LNA (100 uM) to the muscle bath converted the EFS-induced relaxation to contractions and increased the EFS-induced contractions. EFS-induced contractions were abolished by atropine (1uM) or TTX (1uM). Conclusions: Our study demonstrated that the response to acetylcholine and electrical field stimulation on human gastric fundus and corpus is different with that of human gastric antrum.

Combination of Doxazosin and Sildenafil Exerts an Additive Relaxing Effect Compared with Each Compound Alone on Human Cavernosal and Prostatic Tissue

Phosphodiesterase 5 inhibitors (PDE5) such as sildenafil are first-line treatment for erectile dysfunction (ED). Alpha1 (alpha1)-adrenoceptor antagonists such as doxazosin are indicated for the treatment of patients with lower urinary tract symptoms (LUTS)/benign prostatic hyperplasia (BPH). ED and LUTS/BPH are conditions that are often associated. Accordingly, alpha1-adrenoceptor antagonists and PDE5 inhibitors will be often prescribed in real life setting together. To evaluate the effects of the combination of sildenafil and doxazosin on human cavernosal and prostatic tissue. Prostatic and erectile tissues were obtained from nine to 12 patients, respectively. Patients underwent cystoprostatectomy for infiltrating bladder cancer or penile surgery for penile implant, congenital curvature or Peyronie's disease. In organ baths, prostatic and cavernosal strips were submitted to either concentration-response curves (CRC) to phenylephrine (Phe) or norepinephrine (NE), respectively, in presence of vehicle, sildenafil (10(-6) M, 10(-5) M), doxazosin (10(-8) M, 3.10(-8) M, or 10(-7) M), or a combination of both. Continuous electrical field stimulation (EFS; 32 Hz, 5 ms, 5 seconds, 300 mA) was performed on prostatic strips which were incubated with sildenafil 10(-6) M or vehicle before the successive addition of doxazosin (10(-7) M, 10(-6) M) or vehicle. Cavernosal strips were pre-incubated with doxazosin (10(-9) M, 10(-8) M) or vehicle, then CRC to sildenafil were constructed on NE (3.10(-6) M) precontracted cavernosal strips. Combination of sildenafil and doxazosin exerted a greater relaxing effect on CRC to Phe or NE compared with each compound alone in both tissues. Sildenafil significantly enhanced the relaxing effect of doxazosin on EFS-induced contractions in prostatic strips. Doxazosin significantly increased the ability of sildenafil to inhibit NE-induced contractions in cavernosal strips. Sildenafil and doxazosin reduced adrenergic tone of prostatic and cavernosal smooth muscle and their combination provided a significant benefit when targeting relaxation of both tissues. These experiments provide support for further clinical evaluation of the sildenafil and doxazosin combination in ED patients with LUTS/BPH.

Interaction of hydrocortisone with ATP and adenosine on nerve-mediated contractions of frog skeletal muscle

The inhibitory effects of ATP and adenosine on the nerve-mediated contractile responses of isolated sartorius muscle of the frog, Rana ridibunda, evoked by electrical field stimulation (EFS) were studied using pharmacological organ-bath technique. The effects of hydrocortisone applied in vitro and in vivo on contractility of sartorius muscle were also examined. ATP (100 μM) significantly reduced the amplitude of contraction to EFS of sartorius muscle, while pyridoxalphosphate-6-azonphenyl-2′,4′-disulfonic acid (PPADS; 10 μM), a P2 receptor antagonist, abolished inhibitory effect of ATP. A similar inhibitory effect of adenosine (100 μM) was fully antagonized by 8-( p-sulfophenyl)-theophylline (8-SPT, 100 μM), a P1 receptor antagonist. Incubation of the tissue with hydrocortisone (10 μM) caused a slight, but significant, decrease of muscle contractions. After incubation of muscle preparations with both hydrocortisone and ATP, no inhibition of muscle contractility was registered. A single injection of hydrocortisone (100 mg/kg) 12 h prior to experiments to frogs did not significantly change the nerve-mediated contractility of isolated sartorius muscle; however, it abolished the inhibitory action of ATP without changing inhibitory activity of adenosine. After treatment of frogs with hydrocortisone for 14 days (100 mg/kg/day), both ATP and adenosine retained their inhibitory action on EFS-induced contractions of the muscle, and their effects were antagonized by PPADS and 8-SPT, respectively. It is concluded that hydrocortisone has antagonistic actions against the inhibitory effects of ATP at the frog neuromuscular junction, although this effect is lost following long-term treatment with hydrocortisone.

The Influences of G Proteins, Ca2+, and K+ Channels on Electrical Field Stimulation in Cat Esophageal Smooth Muscle

NO released by myenteric neurons controls the off contraction induced by electrical field stimulation (EFS) in distal esophageal smooth muscle, but in the presence of nitric oxide synthase (NOS) inhibitor, L-NAME, contraction by EFS occurs at the same time. The authors investigated the intracellular signaling pathways related with G protein and ionic channel EFS-induced contraction using cat esophageal muscles. EFS-induced contractions were significantly suppressed by tetrodotoxin (1 microM) and atropine (1 microM). Furthermore, nimodipine inhibited both on and off contractions by EFS in a concentration dependent meaner. The characteristics of 'on' and 'off' contraction and the effects of G-proteins, phospholipase, and K(+) channel on EFS-induced contraction in smooth muscle were also investigated. Pertussis toxin (PTX, a G(i) inactivator) attenuated both EFS-induced contractions. Cholera toxin (CTX, G(s) inactivator) also decreased the amplitudes of EFS-induced off and on contractions. However, phospholipase inhibitors did not affect these contractions. Pinacidil (a K(+) channel opener) decreased these contractions, and tetraethylammonium (TEA, K(+) (Ca) channel blocker) increased them. These results suggest that EFS-induced on and off contractions can be mediated by the activations Gi or Gs proteins, and that L-type Ca(2+) channel may be activated by G-protein alpha subunits. Furthermore, K(+) (Ca)-channel involve in the depolarization of esophageal smooth muscle. Further studies are required to characterize the physiological regulation of Ca(2+) channel and to investigate the effects of other K(+) channels on EFS-induced on and off contractions.

Modulation of Noradrenergic Neurotransmission in Isolated Rat Radial Artery

The present study was designed to characterize the neurogenic contraction of rat radial artery. Electrical field stimulation (EFS) evoked frequency-dependent contraction that was abolished by tetrodotoxin (neuronal Na+ channel blocker), guanethidine (sympathetic neuron blocker), or phentolamine (α-adrenoceptor blocker). The α1-adrenoceptor antagonist prazosin inhibited endothelium-independent contractions to EFS, noradrenaline (NA), and the α1-adrenoceptor agonist phenylephrine. Rauwolscine, an α2-adrenoceptor antagonist, augmented nerve-mediated contractions and reduced sensitivity to NA and the α2-adrenoceptor agonist BHT-920. The β-adrenoceptor antagonist propranolol diminished EFS-elicited contractions, while sensitivity to NA was enhanced by propranolol. Relaxations evoked by isoproterenol, a β-adrenoceptor agonist, were abolished by propranolol. NG-Nitro-L-arginine (L-NOARG), a nitric oxide (NO) synthase inhibitor, increased both nerve-mediated and NA-induced responses in endothelium-intact, but not in endothelium-denuded arteries. Moreover, endothelium-dependent responses to BHT-920 and isoproterenol were modified by L-NOARG. Tetraethylammonium (TEA) or 4-amynopyridine, the Ca2+-activated (KCa) or voltage-dependent K+ (KV) channel blockers, respectively, enhanced the neurogenic contractions observed. TEA but not 4-amynopyridine increased NA-induced contractions. The ATP-sensitive K+ (KATP)–channel blocker glibenclamide failed to modify adrenergic contractions. Blockade of capsaicin-sensitive primary afferents increased EFS-induced contractions. In conclusion, adrenergic contractions are predominantly mediated by muscular α1-adrenoceptors, while endothelial α2- and β-adrenoceptors play a minor role. Presynaptic α2- and β-adrenoceptors cannot be precluded. Noradrenergic neurotransmission in rat radial artery seems to be modulated by both stimulation of endothelial NO, KCa, and KV channels and sensory C-fiber activation.

Alteration of cholinergic, purinergic and sensory neurotransmission in the mouse colon of food allergy model

It is well known that intestinal anaphylaxis results in a disturbed intestinal motility. It is hypothesized that the chronic intestinal anaphylaxis-induced changes in the enteric neuronal circuitry cause intestinal motor malfunctions. However, detailed mechanisms largely remain unclear. The aim of this study was to investigate the pathophysiological role of ATP, which acts as a non-cholinergic neurotransmitter and a neuroimmune modulator, in a disturbed intestinal motility of food allergy (FA). The FA mice developed allergic diarrhea accompanied with chronic inflammation and mast cell hyperplasia in the colon. The excised proximal colons (PCs) were suspended in the longitudinal direction in organ baths. In the PCs precontracted by KCl (50 mM), contractile responses to exogenous ATP (1 mM) were significantly ( P < 0.01) higher in FA mice (34.2% of KCl-induced precontractions) as compared to control mice (17.2%). Pretreatment with P2 purinoceptor antagonists [suramin and PPADs] significantly ( P < 0.01) reduced the ATP-evoked contractions to 7.7% and 1.5% in FA and control PCs, respectively. Furthermore, in the presence of inhibitors of cholinergic nerves and capsaicin-sensitive sensory nerves the electrical field stimulation (EFS; 10 Hz)-evoked contractions were significantly ( P < 0.05) higher in FA mice (65.8% of EFS-evoked maximum contractions, n = 6) than those in control mice (47.9%, n = 6). In addition, cumulative application of suramin and PPADs further inhibited EFS-induced contractions by 21.7% in FA mice ( n = 6, P < 0.01) and 8.7% in control mice ( n = 6, P < 0.05). Thus, the present study suggests that the sustained alteration in cholinergic, purinergic and sensory neurotransmission contribute to the disturbed motility during the chronic intestinal anaphylaxis.

In vitro Effect of Amikacin on Rat and Human Detrusor Muscle Contraction

Introduction: Normal and abnormal bladder contractions are principally mediated by acetylcholine released from postganglionic parasympathetic nerves. Since amikacin was reported to affect neurotransmission by a prejunctional mechanism, we investigated the effect of amikacin on isolated detrusor smooth muscle contraction to further evaluate its potential relaxant properties. Materials and Methods: Detrusor smooth muscle obtained from 15 rats and 8 patients undergoing surgery were studied through measurement of isometric muscular contraction induced with electrical field stimulation (EFS) (10–60 Hz), carbachol (10^–7 to 10^–3M) and nicotine (10^–7 to 10^–3M) in the presence or absence of 1 mM amikacin in a low-Ca medium. Results: Amikacin (1 mM) significantly reduced EFS-induced contraction of isolated rat and human detrusor muscle by 33 ± 6.57% (p < 0.005) and 40 ± 1.14% (p < 0.001), respectively. Contraction was restored after addition of calcium chloride (1 mM). The effect of amikacin was comparable to that of magnesium ions. Rat and human detrusor contractile response to nicotine was inhibited by 70 ± 8.27% (p < 0.001) and 64 ± 14.09% (p < 0.01) after the addition of amikacin (1 mM), while no significant effect was observed on carbachol-induced stimulation. Conclusion: Amikacin significantly inhibited detrusor contraction evoked by prejunctional stimulation in vitro, suggesting a depressant effect on autonomic neurotransmission in urinary bladder.

Inhibition of prostate efferent neurotrasmission by amikacin

It has been suggested that manipulation of the autonomic nerve supply to the prostate leads to loss of functional and structural integrity of the gland, and that these changes may be useful in treating prostatic diseases. This study investigates the effect of amikacin on prostate efferent neurotransmission in vitro, in both rat and human prostate samples. Prostate samples, obtained from male Wistar rats and 8 patients undergoing endoscopic surgery for benign prostatic hyperplasia, were studied by measurement of isometric contraction induced by electrical field stimulation (EFS), noradrenalin, carbachol, serotonin and ATP, in the presence or absence of amikacin 10(-3) M in a low-Ca medium. Amikacin significantly reduced EFS-induced contraction of isolated rat and human prostate samples by 45 +/- 6.5% (P < 0.01) and 47 +/- 6% (P < 0.01), respectively. Contraction was restored after addition of calcium chloride 2 x 10(-3) M. Amikacin-induced relaxation in rat prostate samples was greater than the effect of magnesium and weaker than those of prazosin and verapamil, but comparable in extent with the latter. No significant effect was observed on rat prostate contractile response to noradrenaline as to ATP in the presence of amikacin. Rat prostate contraction to carbachol and serotonin was inhibited by 35 +/- 11% (P < 0.05) and 59 +/- 11.7% (P < 0.01), respectively, after addition of amikacin 10(-3) M. Amikacin reduces in vitro both rat and human prostate contraction elicited by pre-junctional stimulation, but does not affect prostate contraction evoked by post-junctional stimulation. Our results indicate that amikacin affects prostatic efferent neurotransmission.

Superoxide anion mediates angiotensin II-induced potentiation of contractile response to sympathetic stimulation

Angiotensin II is known to potentiate vasoconstriction induced by electrical field stimulation (EFS), but the underlying mechanisms for this potentiation are not fully understood. This study was designed to investigate the role of superoxide anion in the potentiation effects of angiotensin II. Contraction of rat mesenteric arterial segments was induced by perivascular nerve stimulation with EFS, and superoxide production was measured with lucigenin-enhanced chemiluminescence. Extracellular signal-regulated kinase (ERK) phosphorylation was determined in cultured smooth muscle cells with Western blot. Angiotensin II concentration dependently potentiated the contraction of rat mesenteric arteries to EFS, which is frequency-dependent. This potentiation was blunted by an angiotensin AT1 receptor antagonist (2-ethoxy-1-[[2′-(1H-tetrazol-5-yl)biphenyl-4-yl]methyl]-1H-benzimidazole-7-carboxylic acid, CV-11974), NAD(P)H oxidase inhibitor (apocynin), superoxide dismutase (SOD) and its mimetic tiron, but not affected by angiotensin AT2 receptor antagonist and inhibitors of xanthine oxidase, cytochrome P450, and cyclooxygenase. Angiotensin II increased superoxide production by mesenteric arteries, which was blunted by angiotensin AT1 receptor antagonist CV-11974, and NAD(P)H oxidase inhibitor apocynin. Superoxide generating compound pyrogallol mimicked the effects of angiotensin II. Tyrosine kinase inhibitor (tyrphostin A25) and mitogen-activated protein kinase (MAPK)/ERK inhibitors (1,4-diamino-2,3-dicyano-1,4-bis [2-aminophenylthio]butadiene (U 0126)) inhibited angiotensin II- and pyrogallol-induced potentiation of EFS-induced contraction, while inactive forms of these inhibitors did not show any inhibitory effects. In cultured smooth muscle cells from mesenteric arteries, angiotensin II and superoxide similarly induced ERK phosphorylation. These results showed that superoxide mediated angiotensin II-induced potentiation of contractile response to EFS and tyrosine kinase-MAPK/ERK activation was involved.

Orchidectomy increases the formation of non-endothelial thromboxane A2 and modulates its role in the electrical field stimulation-induced response in rat mesenteric artery

The aim of this study was to analyze whether endogenous male sex hormones influence the release of thromboxane A2(TXA2) and its role in the electrical field stimulation (EFS)-induced response, as well as the mechanism involved. For this purpose, endothelium-denuded mesenteric arteries from control and orchidectomized male Sprague-Dawley rats were used to measure TXA2 release; EFS-induced response, nitric oxide (NO), norepinephrine (NA), and prostaglandin (PG) I2 release were also measured in the presence of the TXA2 synthesis inhibitor furegrelate. Orchidectomy increased basal and EFS-induced TXA2 release. Furegrelate decreased the EFS-induced contraction in arteries from control rats, but did not modify it in arteries from orchidectomized rats. The EFS-induced neuronal NO release and vasodilator response were increased by furegrelate in arteries from control rats, but were not modified in arteries from orchidectomized rats. Furegrelate did not modify the EFS-induced NA release or vasoconstrictor response in arteries from either control or orchidectomized rats. The EFS-induced PGI2 release was not modified by furegrelate in arteries from control rats, but was increased in arteries from orchidectomized rats. The results of the present study show that endogenous male sex hormone deprivation i) increases non-endothelial TXA2 release and ii) regulates the effect of endogenous TXA2 on the EFS-induced response through different mechanisms that, at the least, involve the NO and PGI2 systems. In arteries from control rats, inhibition of TXA2 formation decreases the EFS-induced response by increasing neuronal NO release. In arteries from orchidectomized rats, the EFS-induced response is unaltered after the inhibition of TXA2 formation, by increasing PGI2 release.

Pharmacological Effects of Solifenacin on Human Isolated Urinary Bladder

To investigate the effects of solifenacin on human detrusor smooth muscles, we evaluate the effects of solifenacin on the contractions induced by carbachol, KCl, CaCl₂ and electrical field stimulation (EFS), and the EFS-induced acetylcholine release from detrusor smooth muscle strips by using the muscle bath and microdialysis technique. The effects of solifenacin were also compared with effects of other antimuscarinic agents (atropine, oxybutynin and propiverine). Pretreatment with various antimuscarinic agents caused parallel shifts to the right of the concentration-response curves to carbachol. The pA₂ value of the Schild plots for solifenacin was similar to that for oxybutynin. Atropine did not inhibit the KCl- and CaCl₂-induced contractions, while solifenacin, oxybutynin and propiverine significantly inhibited these contractions. EFS-induced contractions were inhibited by various antimuscarinic drugs in a concentration-dependent manner. In the presence of atropine, solifenacin tended to inhibit the residual atropine-resistant contractions induced by EFS, but it was not significant. However, oxybutynin and propiverine inhibited them under the same conditions. Although pretreatment with atropine and propiverine did not cause significant changes in EFS-induced acetylcholine release, solifenacin and oxybutynin caused significant decreases in acetylcholine release. The present results suggest that solifenacin inhibits contractions of human detrusor smooth muscles mainly by the antimuscarinic action and that the high concentration of solifenacin has Ca²⁺ channel antagonist action. Moreover, solifenacin may block not only postjunctional receptors, but also prejunctional receptors to modulate acetylcholine releases in cholinergic nerve endings in human detrusor smooth muscles. The findings support that muscarinic-receptor-inhibitory actions in human bladder mainly contribute to the usefulness of solifenacin as a therapeutic drug for overactive bladder.