The response of the circular muscle layer of the guinea-pig isolated vas deferens to transmural electrical stimulation.
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1 Four preparations are described for the isolation of the response of the circular muscle of the guinea-pig vas deferens. These are the ;Furchgott' strip, the ;Vane' strip, the chain preparation and the perfused preparation.2 The four preparations were stimulated transmurally with pulses of supramaximal voltage. The threshold pulse width to which the strips and the perfused preparation responded was 0.025 ms and the maximum responses occurred at 0.1 ms. The threshold frequency was 2 Hz for strip and perfused preparations, the maxima being 20 or 50 Hz for strip preparations and 100 Hz for perfused preparations. The effect of varying the number of pulses per train was also investigated on the perfused vas. Responses occurred to train lengths of 8, 16, 32, 128 pulses, the maximum response being given at 128 pulses at 100 Hz; 256 pulses per train did not produce a further increase in response. The perfused preparation exhibited an after-response at certain frequencies and train lengths.3 Tetrodotoxin and the local anaesthetics, procaine and lignocaine, reversibly abolished the responses of strip and perfused preparations to transmural stimulation.4 The response to intramural nerve fibre stimulation was abolished by guanethidine or bethanidine; this abolition was reversed by dexamphetamine. Noradrenaline contracted strip preparations of circular muscle and raised the pressure in perfused preparations; noradrenaline was competitively antagonized by thymoxamine. The major part of the motor innervation of the circular layer seems to be noradrenergic. (+info)
Many human neurodegenerative diseases are characterized by the idiopathic death of cells narrowly restricted to a subset of neurons in a specific functional neuroanatomic system. Few in vivo models exist for the analysis of these types of degeneration. This report documents the death of sympathetic neurons resident in the superior cervical ganglia of rats after exposure to an exogenous chemical agent, the drug guanethidine, as being mediated by natural killer (NK) cells. This is the first in vivo model of a disorder of the nervous system in which NK cells appear to be the principal effector cell, and thus could serve a central role in dissecting the normal and pathological function of NK cells. In addition, this pathogenetic mechanism appears to represent a novel type of autoimmune reaction that could have a direct bearing on a number of human illnesses. (+info)
Influence of relaxin on the neurally induced relaxant responses of the mouse gastric fundus.
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The peptide hormone relaxin has been reported to depress the amplitude of contractile responses in the mouse gastric fundus by upregulating nitric oxide (NO) biosynthesis at the neural level. In the present study, we investigated whether relaxin also influenced nonadrenergic, noncholinergic (NANC) gastric relaxant responses in mice. Female mice in proestrus or estrus were treated for 18 h with relaxin (1 microg s.c.) or vehicle (controls). Mechanical responses of gastric fundal strips were recorded via force-displacement transducers. In carbachol precontracted strips from control mice and in the presence of guanethidine, electrical field stimulation (EFS) elicited fast relaxant responses that may be followed by a sustained relaxation. All relaxant responses were abolished by tetrodotoxin. Relaxin increased the amplitude of the EFS-induced fast relaxation without affecting either the sustained one or the direct smooth muscle response to papaverine. In the presence of the NO synthesis inhibitor L-N(G)-nitro arginine (L-NNA), that abolished the EFS-induced fast relaxation without influencing the sustained one, relaxin was ineffective. In strips from relaxin-pretreated mice, EFS-induced fast relaxations were enhanced in amplitude with respect to the controls, while sustained ones as well as direct smooth muscle responses to papaverine were not changed. Further addition of relaxin to the bath medium did not influence neurally induced fast relaxant responses, whereas L-NNA did. In conclusion, in the mouse gastric fundus, relaxin enhances the neurally induced nitrergic relaxant responses acting at the neural level. (+info)
Expression of Rho-kinase (ROCK-1 and ROCK-2) and its substantial role in the contractile activity of the sheep ureter.
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Expression of two isoforms of Rho-kinase (ROCK) and its functional role in the physiological control of smooth muscle contraction in the sheep ureter were investigated. Helical strips of the ureteric smooth muscle were stimulated by electrical field stimulation (EFS, 60 V, 1 mS, 2, 4, 8, 16 and 32 Hz, for 20 S), KCl (80 mm), carbachol (CCh, 10(-8)-10(-4) m) or phenylephrine (Phe, 10(-8)-10(-4) m). EFS produced a reproducible contractile activity, which was abolished by tetrodotoxin (3 x 10(-6) m), a Na(+) channel blocker. A muscarinic receptor antagonist, atropine (2 x 10(-6) m), and an adrenergic neuron blocker, guanethidine (10(-5) m), significantly suppressed the contraction induced by EFS. However, this contraction was augmented in the presence of N(G)-nitro-l-arginine (l-NA, 10(-4) m), a nitric oxide synthase inhibitor. Two Rho-kinase inhibitors, Y-27632 (5 x 10(-5) m) and fasudil (5 x 10(-5) m), markedly attenuated the EFS-elicited contraction. CCh and Phe produced concentration-dependent contraction in the sheep ureter. pD(2) values for Phe and CCh were 5.04+/-0.11 and 5.00+/-0.22, respectively. Y-27632 (5 x 10(-5) m) and fasudil (5 x 10(-5) m) also significantly inhibited CCh- and Phe-induced contractions. Moreover, these ROCK inhibitors produced relaxations in the KCl-elicited contraction in a concentration-dependent manner. pD(2) values for Y-27632 and fasudil were, respectively, 5.17+/-0.07 and 4.58+/-0.08 (P<0.001). Furthermore, the influences of these agents were also tested on spontaneous phasic contractions of the tissue. Among Y-27632, fasudil, TTX, l-NA, guanethidine and atropine, only the ROCK inhibitors (10(-6)-10(-5) m) were able to suppress the spontaneous contractile activity. Western blot analysis has revealed that both isoforms of Rho-kinase (ROCK-1 and ROCK-2) are expressed in the sheep ureter. Densitometric analysis has indicated that these enzymes are less expressed in the sheep ureter than are in the sheep aorta in a significant manner. These results show that a contractile enzyme, Rho-kinase, is expressed, and it mediates agonist- and EFS-induced contractions as well as spontaneous contractile activity of the isolated sheep ureter. Since Y-27632 and fasudil depressed the contractions, it seems plausible to postulate that Rho-kinase inhibitors may be beneficial in the treatment of renal colic. (+info)
Release of beta-nicotinamide adenine dinucleotide upon stimulation of postganglionic nerve terminals in blood vessels and urinary bladder.
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Chemical signaling in autonomic neuromuscular transmission involves agents that function as neurotransmitters and/or neuromodulators. Using high performance liquid chromatography techniques with fluorescence and electrochemical detection we observed that, in addition to ATP and norepinephrine (NE), electrical field stimulation (EFS, 4-16 Hz, 0.1-0.3 ms, 15 V, 60-120 s) of isolated vascular and non-vascular preparations co-releases a previously unidentified compound with apparent nucleotide or nucleoside structure. Extensive screening of more than 25 nucleotides and nucleosides followed by detailed peak identification revealed that beta-nicotinamide adenine dinucleotide (beta-NAD) is released in tissue superfusates upon EFS of canine mesenteric artery (CMA), canine urinary bladder, and murine urinary bladder in the amounts of 7.1 +/- 0.7, 26.5 +/- 4.5, and 15.1 +/- 3.2 fmol/mg of tissue, respectively. Smaller amounts of the beta-NAD metabolites cyclic adenosine 5'-diphosphoribose (cADPR) and ADPR were also present in the superfusates collected during EFS of CMA (2.5 +/- 0.9 and 5.8 +/- 0.8 fmol/mg of tissue, respectively), canine urinary bladder (1.8 +/- 0.5 and 9.0 +/- 6.0 fmol/mg of tissue, respectively), and murine urinary bladder (1.4 +/- 0.1 and 6.2 +/- 2.4 fmol/mg of tissue, respectively). The three nucleotides were also detected in the samples collected before EFS (0.2-1.6 fmol/mg of tissue). Exogenous beta-NAD, cADPR, and ADPR (all 100 nm) reduced the release of NE in CMA at 16 Hz from 27.8 +/- 6.0 fmol/mg of tissue to 15.5 +/- 5.0, 12 +/- 3.0, and 10.0 +/- 4.0 fmol/mg of tissue, respectively. In conclusion, we detected constitutive and nerve-evoked overflow of beta-NAD, cADPR, and ADPR in vascular and non-vascular smooth muscles, beta-NAD being the prevailing compound. These substances modulate the release of NE, implicating novel nucleotide mechanisms of autonomic nervous system control of smooth muscle. (+info)
Protein metabolism in guanethidine-treated rats.
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The aim of the present study was to evaluate the effect of short-term adrenergic blockade on the rate of whole-body protein turnover and leucine oxidation, and on protein synthesis in specific tissues in male rats. Adrenergic blockade was induced by guanethidine (100 mg/kg body weight subcutaneously). The control group was treated with saline. On the second day, the parameters of whole-body protein and leucine metabolism were evaluated using a primed constant intravenous infusion of L-[1-(14)C]leucine. Protein synthesis in tissues was determined on the basis of L-[1-(14)C]leucine incorporation. Guanethidine treatment caused a decrease in norepinephrine in skeletal muscle. Whole-body leucine oxidation and leucine oxidized fraction were higher in guanethidine-treated rats. There was an insignificant effect of guanethidine on whole-body proteolysis, protein synthesis and leucine clearance. However, protein balance was negative due to the larger difference between protein synthesis and proteolysis in guanethidine-treated animals compared to controls. In guanethidine-treated rats, protein synthesis was higher in the gastrocnemius muscle and in the kidneys and lower in liver and spleen. Changes in the small intestine and colon were insignificant. In addition, a marked decrease in concentration of several amino acids has been observed in the liver, the kidneys and the spleen. It is concluded that adrenergic blockade induced by guanethidine is associated with significant changes in protein metabolism, leucine oxidation and amino acid concentrations in several tissues. The most important consequences of treatment are considered to be a negative effect on protein balance, increased protein turnover in skeletal muscle and kidneys and decreased protein synthesis in the liver and spleen. These changes may also be induced by administration of other sympathetic blocking agents, e.g. in treatment of hypertension. (+info)
Vanilloid receptor TRPV1, sensory C-fibers, and vascular autoregulation: a novel mechanism involved in myogenic constriction.
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Myogenic constriction describes the innate ability of resistance arteries to constrict in response to elevations in intraluminal pressure and is a fundamental determinant of peripheral resistance and, hence, organ perfusion and systemic blood pressure. However, the receptor/cell-type that senses changes in pressure on the blood vessel wall and the pathway that couples this to constriction of vascular smooth muscle remain unclear. In this study, we show that elevation of intraluminal transmural pressure of mesenteric small arteries in vitro results in a myogenic response that is profoundly suppressed following ablation of sensory C-fiber activity (using in vitro capsaicin desensitization resulted in 72.8+/-10.3% inhibition, n=8; P<0.05). Activation of C-fiber nerve endings by pressure was attributable to stimulation of neuronal vanilloid receptor, TRPV1, because blockers of this channel, capsazepine (71.9+/-11.1% inhibition, n=9; P<0.001) and ruthenium red (46.1+/-11.7% inhibition, n=4; P<0.05), suppressed the myogenic constriction. In addition, this C-fiber dependency is likely related to neuropeptide substance P release and activity because blockade of tachykinin NK1 receptors (66.3+/-13.7% inhibition, n=6; P<0.001), and not NK2 receptors (n=4, NS), almost abolished the myogenic response. Previous studies support a role for 20-hydroxyeicosatetraenoic acid (20-HETE) in myogenic constriction responses; herein, we show that 20-HETE-induced constriction of mesenteric resistance arteries is blocked by capsazepine. Together, these results suggest that elevation of intraluminal pressure is associated with generation of 20-HETE that, in turn, activates TRPV1 on C-fiber nerve endings resulting in depolarization of nerves and consequent vasoactive neuropeptide release. These findings identify a novel mechanism contributing to Bayliss' myogenic constriction and highlights an alternative pathway that may be targeted in the therapeutics of vascular disease, such as hypertension, where enhanced myogenic constriction plays a role in the pathogenesis. (+info)
Participation of ATP in nonadrenergic, noncholinergic relaxation of longitudinal muscle of wistar rat jejunum.
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A role of ATP in nonadrenergic, noncholinergic (NANC) relaxations was examined in the Wistar rat jejunum. Electrical field stimulation (EFS) induced NANC relaxation of longitudinal muscle of the jejunal segments in a frequency-dependent manner. A purinoceptor antagonist, adenosine 3'-phosphate 5'-phosphosulfate (A3P5PS, 100 muM) inhibited the relaxation: relaxations induced by EFS at lower or higher frequencies were either completely or partially inhibited, respectively. After the jejunal segments had been desensitized to ATP, the relaxations were decreased to the same extent as those inhibited by A3P5PS. An inhibitor of small conductance Ca(2+)-activated K(+) channels (SK channels), apamin (100 nM), completely inhibited EFS-induced relaxations. Treatment of the segments with an inhibitor of sarcoplasmic reticulum Ca(2+)-ATPase, thapsigargin (1 muM), significantly inhibited the relaxations. The exogenous ATP-induced relaxation of longitudinal muscle occurred with a concomitant decrease in intracellular Ca(2+) levels. Apamin and thapsigargin abolished these ATP-induced responses. A3P5PS significantly inhibited the inhibitory junction potentials which were induced in the longitudinal muscle cells. In addition, apamin significantly inhibited the hyperpolarization that was induced by exogenous ATP in the cells. These findings in the Wistar rat jejunum suggest that ATP participates in the NANC relaxation via activation of SK channels induced by Ca(2+) ions that are released from the thapsigargin-sensitive store site. (+info)