Response Of Smooth Muscle Strips Research Articles

Effect of Gonadal Hormones on Colonic Contractile Activity in Albino Rats

Sex differences were reported in Irritable Bowel Syndrome. We aimed to demonstrate the effect of gonadal hormones on colonic contractile activity. In this study, we performed in vitro measurements of colonic contractile activity in longitudinal smooth muscle strips of female and male Albino rats. After administration of a gonadal hormone (estrogen (EST), progesterone (PROG) and testosterone (TEST)) or ethanol (ETH) solution as control, stimulation with acetylcholine (ACh) or inhibition with norepinephrine (NE) was performed. We found that increasing doses of EST resulted in a stepwise inhibition of SCCA in both sexes and inhibited the ACh effect in females. Similarly, high dose PROG inhibited SCCA in females. TEST inhibited SCCA in males but not Ach induced contractions. TEST reduced the inhibitory effect of NE in female rats. In conclusion, exposure of colonic smooth muscle strips to gonadal hormones led to sex-dependent changes in SCCA and modified the response of smooth muscle strips to both pro-contractile and anti-contractile neurotransmitters.

In vitro spontaneous contractile activity of colonic smooth muscle in naive Lewis rats: Acute effect of gonadal hormones.

Functional gastrointestinal disorders affect females more often. Changes in colonic motility may be etiological co-factors for the clinical symptoms. The aim of the present study was to analyze the influence of gonadal hormones on colonic contractile activity. In vitro measurements of colonic contractile activity in longitudinal smooth muscle strips of female and male Lewis rats were performed in an organ chamber experiment. After the administration of a gonadal hormone estradiol [EST], progesterone [PROG] and testosterone [TEST]) or ethanol solution as control, stimulation with acetylcholine (ACh) or inhibition with norepinephrine (NE) was performed. Compared to the smooth muscle strips of male rats, significantly higher spontaneous colonic contractile activity (SCCA) was observed in female animals. Increasing doses of ACh showed the progressive stimulation of SCCA whereas rising doses of NE resulted in a stepwise inhibition of SCCA, respectively. EST superfusion displayed an inhibitory effect on SCCA in both sexes and inhibited the ACh effect in female rats. Similarly, acute superfusion with high-dose PROG inhibited SCCA in females. Acute TEST superfusion inhibited SCCA in males and led to significant higher colonic contractile activity in males following subsequent stimulation with ACh. In female rats, the inhibitory effect of NE was reduced by prior exposure to TEST. In our in vitro study the acute exposure of colonic smooth muscle tissue to gonadal hormones led to sex-dependent changes in SCCA and translated in a modified response of smooth muscle strips to both pro-contractile and anti-contractile neurotransmitters.

The role of nitric oxide on the dysfunction of intestinal motility in rats subjected to hemorrhagic shock

To determine the role of nitric oxide (NO) in intestinal motility dysfunction in rats subjected to hemorrhagic shock (HS). Sixteen male Wistar rats were randomly and equally divided into two groups. The HS model of rat was induced by bleeding from femoral artery. After animal models were made, different inducers were added, and duodenum samples were harvested for the determination of contractile response to acetylcholine (ACh) in vitro, activities of inducible nitric oxide synthase (iNOS), contents of NO in tissue, and morphological changes. The spontaneous contraction of intestinal smooth muscle and contractile response induced by ACh were significantly decreased at 180 minutes in HS group, compared with control group, the contractile response induced by ACh of intestinal smooth muscle was decreased by almost 60% (0.40±0.11 g×mm(-2)×s(-1) vs. 1.00±0.20 g×mm(-2)×s(-1), P<0.01). The inhibitor of iNOS N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) could significantly restore the suppressed contractile response of smooth muscle strips obtained from HS rats (0.97±0.25 vs. 0.40±0.11, P<0.01). Moreover, the inhibitor of soluble guanylyl cyclase 1H-[1,2,4] Oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) also improved the contractility of HS muscle strips significantly (0.79±0.17 vs. 0.40±0.11, P<0.01). But the blocker of ATP-sensitive potassium channel glibenclamide had no effect on the contractility of HS muscle strips (0.47±0.14 vs. 0.40±0.11, P>0.05). Compared with those of control group, iNOS activities (2.295±0.310 U/g vs. 1.319±0.322 U/g) and NO contents (2.880±0.353 μmol/g vs. 1.505±0.387 μmol/g) in duodenum of HS rats were both significantly increased (both P<0.01). Under light microscopy, the most significant morphological change in duodenum following HS was the infiltration of obvious inflammatory cells. The NO produced by the overexpression of iNOS induced by HS involves in the motility dysfunction of intestine through the mechanism of cyclic guanosine monophosphate (cGMP) system. Moreover, NO-mediated infiltration of inflammatory cells in tissue may also contribute to the development of motility dysfunction of intestine following HS.

Gastric motility in ghrelin receptor knockout mice

The aim of this study was to investigate the effects and possible mechanisms of ghrelin receptor (GHS-R) deficiency on gastric motility in GHS-R deficient (Ghsr-/-) mice. Ghsr-/- and control (Ghsr+/+) mice were genotyped by PCR. The percentage of gastric emptying (GE%) was calculated following the intraperitoneal adminis-tration of ghrelin. Invitro, the contractile response of smooth muscle strips to ghrelin and electrical field stimulation (EFS) and the intraluminal pressure change of isolated stomach to carbachol were observed in an organ bath. The staining of nerve cells in the gastric muscle layer was performed by immunofluorescence. Delayed gastric emptying was observed in the Ghsr-/- mice; ghrelin enhanced the GE% in the Ghsr+/+ mice but had no effect on the GE% in the Ghsr-/- mice. Invitro, the response of the strips to ghrelin and EFS and the intraluminal pressure change to cabarchol was reduced in the Ghsr-/- mice. GHS-Rs were predominantly expressed on nerve cells in gastric muscle layers. The number of nerve cells was observed to be decreased in the Ghsr-/- mice. The delayed gastric emptying may relate to the loss of GHS-Rs and the reduction in the number of nerve cells in the gastric muscle layers of the GHS-R-deficient mice.

Effects of trimebutine maleate on colonic motility through Ca2+-activated K+ channels and L-type Ca2+ channels

The effects of trimebutine maleate (TM) on spontaneous contractions of colonic longitudinal muscle were investigated in guinea pigs. The contractile responses of smooth muscle strips were recorded by an isometric force transducer. Membrane and action potentials were detected by an intracellular microelectrode technique. The whole-cell patch clamp recording technique was used to record the changes in large conductance Ca(2+)-activated K(+) (BK(ca)) and L-type Ca(2+) currents in colonic smooth muscle cells. At high concentrations (30, 100, and 300 μM), TM inhibited the amplitude of spontaneous contractions. At low concentrations (1 and 10 μM), TM attenuated the frequency and tone of smooth muscle strips, whereas TM had no influence on the amplitude of spontaneous contractions. TM depolarized the membrane potentials, but decreased the amplitude and frequency of action potentials at high concentrations. TM inhibited BK(ca) and L-type Ca(2+) currents in a dose-dependent manner. In the presence of the BK(ca) channel opener, NS1619, TM also inhibited BK(ca) currents. Bayk8644, a L-type Ca(2+) channel opener, increased L-type Ca(2+) currents. This augmentation was also attenuated by TM. These results suggest that TM attenuates intestinal motility through inhibition of L-type Ca(2+) currents, and depolarizes membrane potentials by reducing BK(ca) currents. Thus, TM may be a multiple-ion channel regulator in the gastrointestinal tract.

Effects of ligustrazine on the contraction of isolated rabbit corpus cavernosum strips

To investigate the role of ligustrazine on relaxation of the isolated rabbit corpus cavernosum tissue in vitro, the effects of ligustrazine on the corpus cavernosum were observed by using experimental method of smooth muscle strips. Concentration-responses to phenylephine (PE) and KCl were recorded. The results showed that ligustrazine concentration-dependently depressed the contraction response of smooth muscle strips induced by PE. The maximum percentage relaxation of cavernosal strips by ligustrazine was 74.1% +/- 6.2% (compared with control: 21.9% +/- 5.6%, P < 0.01). Ligustrazine concentration-dependently reduced the amplitude of the contraction induced by cumulative doses of PE or KCl, shifted the cumulative concentration response curves of PE and KCI to the right and depressed their maximal responses. It was concluded that ligustrazine could significantly relax the cavernosal muscle contraction induced by PE in vitro. The results suggested that ligustrazine inhibited calcium ion influx.

Functional mapping of NPY/PYY receptors in rat and human gastro-intestinal tract

Peptide YY (PYY) is involved in the regulation of several gastro-intestinal functions, including motility. The aims of the present study were (i) to characterize the effects of PYY on smooth muscle strips obtained from the different gastro-intestinal segments in rats and in humans and (ii) to realize a map of the Y receptors expression. Contractions of strips were recorded under isometric conditions, using PYY and acetylcholine as control. We observed that PYY induced a contraction of muscle strips from rat proximal colon, but displayed no effect on other gut segments. Using RT-PCR, mRNA encoding the Y1 and Y4 receptors were detected in muscle strips depending on the segment. In humans, the muscle preparations responded to ACh but not to PYY. Moreover, only Y2 receptor mRNA was found in the ileum and the left colon, but not in other segments. Our study shows the heterogeneity in the expression of Y receptors along the gastro-intestinal tract, and reveals great discrepancies between rats and humans both concerning the expression of Y receptor, and the response of smooth muscle strips to PYY.

A NEW APPROACH TO RECORDING THE ELECTROMYOGRAPHIC ACTIVITY OF DETRUSOR SMOOTH MUSCLE

Extracellular recordings from the whole intact mammalian bladder of the electrical events leading to contraction of the organ have been elusive for almost 50 years despite the widespread potential applications of such a technique. The principal problem is the need to isolate the small real signals reflecting membrane depolarization from the large electromechanical artifact generated as the organ contracts. In this preliminary study we determined whether electrical signals may be isolated and verified as biological using extracellular bipolar reversible suction electrodes. Six whole excised guinea pig bladders were mounted in an especially constructed organ bath. Electrical activity resulting from nerve stimulation of the organ was recorded using a novel 10 bipolar Pt/PtCl suction electrode simultaneously with changes in intravesical pressure. Mechanical and pharmacological control experiments were performed to determine the true origin of these signals. A predominantly biphasic electrical signal of a mean amplitude plus or minus standard deviation of 647 plus or minus 301 microV. and a mean duration of 293 plus or minus 51 milliseconds was consistently recorded from the serosal surface of all guinea pig bladders. In all cases the electrical signal and mechanical response to stimulation were completely abolished by 1 microM. tetrodotoxin. The signal always preceded any change in intravesical pressure. It was sensitive to changes in the CaCl2 concentration of the superfusate, abolished by purinergic but not cholinergic neuromuscular blockade and independent of electromechanical artifact. In this preliminary report we describe a novel technique by which nerve mediated detrusor electrical activity leading to contraction of the whole intact guinea pig bladder may be isolated from artifact and verified as real. We hope that development of this technique may enable its application to the in situ human bladder. However, to our knowledge whether electromyographic activity may be recorded from human detrusor remains to be determined.

AGE-RELATED CHANGES IN CONTRACTILE RESPONSES OF RABBIT LOWER URINARY TRACT TO ENDOTHELIN

AGE-RELATED CHANGES IN CONTRACTILE RESPONSES OF RABBIT LOWER URINARY TRACT TO ENDOTHELIN

Age-related changes in contractile responses of rabbit lower urinary tract to endothelin.

As there are significant amounts of endothelin (ET) receptors in the mammalian urinary tract, we investigated the pharmacological properties and localization of ET receptors in the rabbit lower urinary tract as a function of age. The characteristics of ET receptors in bladder dome, trigone and urethra of 6 weeks and 6 months old male rabbits were determined using muscle bath and autoradiographic techniques. ET-1 produces significant contractile responses in smooth muscle strips from bladder dome, trigone, and urethra in both 6 weeks and 6 months old rabbits. Although there was no significant difference in the maximum contractile response of urethral muscle strips to ET-1 between 6 weeks and 6 months old rabbits, the maximum responses to ET-1 were higher in both bladder dome and trigone of 6 weeks than 6 months old rabbits. A selective ETA receptor antagonist, BQ 610, shifted the concentration response curve to ET-1 to the right without decreasing maximal contractile responses in all regions from both age groups, whereas a selective ETB receptor antagonist, IRL 1038, had no significant effect on the contractile response in these tissues. Autoradiographic studies indicate that both ET receptor subtypes are expressed in bladder dome, trigone, and urethra with the ETA subtype being located only in the smooth muscle layers and the ETB subtype being located in both the urothelial and smooth muscle layers. Our data indicate the presence of region- and age-dependent differences in the contractile properties of ET receptors in the male rabbit lower urinary tract. Although both ETA and ETB receptor subtypes are present in the smooth muscle layers, the ETA receptor is the sub-type that is primarily involved in the mediation of contractions.

Angiontensin II Receptors in the Rat Urinary Bladder Smooth Muscle: Type 1 Subtype Receptors Mediate Contractile Responses

Angiotensin II (Ang II) receptors in the rat urinary bladder smooth muscle were investigated by in vitro responses of smooth muscle strips to exogenous Ang II stimulation and in radioligand binding assays. Ang II (10−10M. to 10−5M.) caused a potent contractile response in a concentration-dependent manner. Using the recently developed nonpeptide subtype-selective antagonists, the Ang II-induced contractile response was further characterized. The Ang II-induced contractile response was inhibited weakly by the type 2 subtype (AT2)-selective antagonist PD123319 but was potently inhibited by the type 1 subtype (ΑΤ1)-selective antagonist DuP 753 with a pA2 value of 9.03, suggesting that the response is mediated predominantly by ΑΤ1 receptors. [125I]Ang II was used to specifically label a single class of binding sites with a dissociation constant of 0.31nM. and a maximal binding capacity of 41.5fmol./mg. of protein. DuP 753 could completely antagonize the binding of Ang II in a particulate fraction of rat bladder (Ki = 14nM.), whereas PD123319 did not have any effect in the concentration range of 10−9 to 10−5M. The results suggest that ΑΤ1 receptors rather than AT2 receptors predominantly mediate Ang II-induced contraction in the rat urinary bladder.

Contractile responses of smooth muscle strips from rat and guinea‐pig urinary bladder to transmural stimulation: effects of atropine and α,β‐methylene ATP

1. Strength-duration curves for threshold mechanical responses to single transmural stimuli were identical for rat and guinea-pig detrusor. In both species atropine had no effect on the curves, but the curves were shifted to the right by nerve blockade with tetrodotoxin (TTX), and by blockade of P2-purinoceptors with alpha,beta-methylene ATP (alpha,beta-MeATP). 2. With short duration pulses of 50 V and less, the responses were nerve-mediated. Increase in either the strength or duration of the stimulus caused direct muscle stimulation, resistant to blockade with atropine, TTX and alpha-beta-MeATP. 3. The shape of the contractile response to a single nerve stimulus varied from tissue to tissue. The responses could be mono-, bi-, or multiphasic. Bi- or multiphasic responses were normally seen in tissues which were spontaneously active. The multiphasic nature of the response was enhanced by factors which increased the excitability of the cells and was reduced by factors which decreased the excitability. 4. The frequency-response curves in the rat are similar to those previously obtained in the guinea-pig. Atropine suppresses the high frequency response by 25%, with little effect at low frequencies, whereas desensitization of P2-purinoceptors with alpha,beta-MeATP suppresses the responses maximally at low frequencies but still by 75% at high frequencies. A combination of both drugs eliminates the nerve-mediated responses. 5. It is concluded that the response to a single nerve stimulus is mediated by a non-cholinergic transmitter, through activation of P2-purinoceptors. The possibility that simultaneous release of acetylcholine can modify the excitability of cells and thus the configuration of the response to a single stimulus is discussed.

Influence of the autonomic nervous system in the horse urinary bladder

alpha and beta-adrenergic receptors in detrusor muscle and bladder base of horses were investigated by in vitro responses of smooth muscle strips to exogenous agonist and antagonist drugs. Noradrenaline, isoprenaline and salbutamol induced relaxation of detrusor muscle strips which was significantly inhibited by propranolol and butoxamine suggesting that the response is mediated by beta-2 adrenergic receptors. In the urinary bladder base noradrenaline, phenylephrine and B-HT 920 induced strong contractile effects. These contractile responses were inhibited by the alpha antagonist phenoxybenzamine, the alpha-1 selective antagonist prazosin and the alpha-2 selective antagonist yohimbine. The inhibitory action of prazosin was more potent than that observed with yohimbine suggesting that the response in the bladder base of horses is mediated predominantly by alpha-1 adrenergic receptors, although alpha-2 receptors also participate.

Responses of smooth muscle strips from penile erectile tissue to drugs and transmural nerve stimulation.

1. The mechanical response to drugs and to electrical stimulation of nerves was investigated in isolated strips of intrinsic smooth muscle from the corpora cavernosa penis of the rat. 2. Noradrenaline caused muscle strips to contract in a dose-dependent manner. Contractions could be blocked by pretreatment with the alpha-adrenoreceptor antagonist, phentolamine. 3. Acetylcholine and carbachol had no effect on the baseline tension of muscle strips. Both drugs were relatively ineffective in relaxing noradrenaline-contracted strips. 4. Field stimulation of isolated muscle strips elicited contractions which were blocked by tetrodotoxin and greatly attenuated with phentolamine or reserpine pretreatment. Acetylcholine inhibited the excitatory response to field stimulation. This inhibitory effect of acetylcholine could be blocked with atropine. 5. Field stimulation of noradrenaline-contracted muscle strips caused relaxation. This inhibitory effect, due to nerves which arise from the pelvic plexus, is unaffected by substances which act on cholinergic systems. 6. The results suggest that the erectile muscle of the rat is similar to that of man in that it receives an excitatory noradrenergic innervation and an inhibitory innervation which may have a non-cholinergic component. Although acetylcholine may have a role in penile physiology of the rat, it is unlikely that it has a postsynaptic action.

Comparative response of smooth muscle strips of bladder and bowel to various pharmacological agents

AbstractIntestinal segments are commonly incorporated in the urinary system as conduits, reservoirs, and as implants in augmentations of bladders. This practice, initiated in 1888 by Tizzone, only became popular in the 1950s. Although both bladder and intestine are composed primarily of smooth muscle, there are significant morphological and functional differences between these tissues. This present study compares the pharmacological properties of intestinal smooth muscle to those of bladder smooth muscle. Ileum was taken as a representative section from small intestine, sigmoid colon from the large bowel, and the bladder body from the urinary bladder.The results can be summarized as follows: Bethanechol (cholinergic agonist) produced a rapid and sustained increase in tension in the bladder, a marked increase in the amplitude and frequency of phasic contractions in the ileum, and a sustained increase in tension in the sigmoid colon. Methoxamine (α‐adrenergic agonist) and ATP (purinergic agonist) produced an increase in tension in the bladder, and reduced the tension in both ileum and sigmoid. Isoproterenol (β‐adrenergic agonist) produced a relaxation in all three tissues.

Effect of lsoproterenol and EGTA on the volume‐pressure relationship of the in vitro whole bladder preparation

AbstractIn a previous study comparing the pharmacological response of smooth muscle strips isolated from rabbit urinary bladder with the response of the whole bladder preparation, we observed that although isoproterenol stimulated a marked decrease in isometric tension in the muscle strips, isoproterenol only slightly decreased intravesical pressure (whole bladder preparation).We have recently modified our whole bladder system so that we can now quantitatively determine the effect of drugs on bladder volume at constant pressure as well as on intravesical pressure at constant volume. Using this system we have reinvestigated the effect of isoproterenol and have demonstrated that although isoproterenol has only a slight effect on intravesical pressure, this minor effect on pressure resulted in a marked increase in whole bladder volume, and a corresponding increase in cystometric compliance.

Autonomic innervation of rabbit urinary bladder following estrogen administration

The effects of estrogen administration on the autonomic innervation of the rabbit urinary bladder were studied. Immature female white rabbits were injected twice daily with estrogen (150 μg./Kg.) for four consecutive days. Control animals received injections of vehicle alone. The adrenergic innervation was identified using the glyoxalic acid method of catecholamine histofluorescence. The cholinergic innervation was visualized utilizing specific acetylcholinesterase staining. Additionally, the effect of estrogen administration on the response of smooth muscle strips of urinary bladder to specific autonomic agonists was determined. Estrogen administration induced a moderate increase in the adrenergic innervation of the rabbit bladder detrusor, whereas no change could be observed in the cholinergic innervation. It should be noted, however, that whereas the adrenergic innervation in the bladder of the control animal was sparse, the cholinergic innervation in the bladder body was quite dense. Estrogen induced a marked increase in the response to alpha -adrenergic (methoxamine) and muscarinic cholinergic (bethanechol) agonists. No alterations were noted in the response to beta-adrenergic agonists (isoproterenol). These findings indicate that the urinary bladder responds as a target organ of estrogen-induced alterations in autonomic innervation.