Concentration-dependent stimulation of cholinergic motor nerves or smooth muscle by [Nle13]motilin in the isolated rabbit gastric antrum

In man, rabbit and cat, the effects of motilin and motilides are neurally mediated in vivo, whereas in vitro binding and contractility studies suggest the presence of a smooth muscular receptor. The aim of this study was to investigate in vitro interactions of motilin with the enteric excitatory neurotransmission in the gastric antrum of the rabbit. Circular muscle strips from the pre-pyloric antrum were subjected to electrical field stimulation (1 ms, 1-32 Hz, 10 s train) and muscle twitch responses were recorded isometrically. Induced twitch responses were frequency dependent (1-32 Hz) and entirely neurogenic (tetrodotoxin sensitive). [Nle13]motilin dose-dependently (10[-9]-10[-8] M) enhanced the amplitude of, atropine sensitive, evoked contractions. At 4 Hz the response, expressed as a % of the response to 32 Hz, increased from 15.5 +/- 4.1% (control) to 28.1 +/- 5.8% (motilin 10[-9] M), and to 45.8 +/- 3.6% (motilin 10[-8.5] M) (P < 0.05). This effect was not inhibited by hexamethonium (10[-3.3] M) but was abolished by the motilin receptor antagonist GM-109 (10[-5] M). In unstimulated strips, motilin induced phasic-tonic contractions with a threshold concentration of 10[-8] M and an pEC50 of 7.48, which were also inhibited by GM-109 (10[-5] M) but not by tetrodotoxin (10[-5.5] M). The maximal tension, frequency and dose-dependency of carbachol-induced contractions were not influenced by motilin (pEC50, carbachol: 6.48 +/- 0.06 (control), 6.49 +/- 0.07 (motilin)). In conclusion, motilin enhances contractions induced by electrical field stimulation in the rabbit antrum by a post-ganglionic interaction with the cholinergic neurotransmission in vitro at low doses and interacts directly with antral smooth muscle at high doses. This model is an accurate reflection of the in vivo effects of motilin and provides a tool to study neurogenic and myogenic actions of motilin and motilides in vitro.     

Heterogeneity of motilin receptors in the gastrointestinal tract of the rabbit

Motilin, a 22-amino acid peptide synthesized in endocrine cells of intestinal mucosa, stimulates GI smooth muscle contractility. To elucidate the mode of action of motilin, we attempted to determine whether motilin receptors are localized on nerve cells or on smooth muscle cells of the GI tract. Mucosa-free tissues from rabbit antrum and duodenum were homogenized separately with a Polytron prior to differential centrifugation to obtain synaptosome or plasma membrane-enriched fractions, as determined by the distribution of [3H]saxitoxin (SAX) binding (neural membranes) and 5' nucleotidase (5'N) activity (smooth muscle plasma membranes). Motilin binding was evaluated by the displacement of [125I]motilin by motilin (1-22) on the various membrane fractions. In the antrum, motilin binding was highly correlated with SAX binding (r = 0.81, p < 0.0005), and also significantly with 5'N activity (r = 0.54, p < 0.05). In the duodenum, motilin binding correlated significantly with 5'N activity (r = 0.67, p < 0.005), but not with SAX binding (r = -0.11, NS). Receptor affinity, for the motilin antagonist MOT(1-12)[CH2NH]10-11, for motilin(1-22), and for the motilin agonist erythromycin lactobionate was significantly (p < 0.001, p < 0.001, and p < 0.05, respectively) higher in SAX-enriched fractions from the antrum than in 5'N-enriched fractions from the duodenum. Therefore, in the rabbit: 1) motilin receptors appear to be predominantly located on nerve tissues in the antrum and restricted to smooth muscle cells in the duodenum, and 2) antral receptors and duodenal receptors displayed different pharmacological characteristics, probably corresponding to two specific and heterogeneous motilin receptor subtypes.     

Serotonin stimulates protein tyrosyl phosphorylation and vascular contraction via tyrosine kinase

Serotonin (5-HT, 5-hydroxytryptamine) is a mitogen in vascular smooth muscle and vascular reactivity to 5-HT is significantly enhanced in hypertension and atherosclerosis. We have tested the hypothesis that tyrosine kinases, enzymes important for mitogenesis, may play a role in 5-HT-induced vascular smooth muscle contractility. Helical strips of rat carotid artery and aorta denuded of endothelium were mounted in tissue baths for measurement of contractile force. The tyrosine kinase inhibitor genistein (5 x 10(-6) M) decreased the potency of 5-HT approximately 4-fold and reduced maximal contraction to 5-HT in carotid arterial strips denuded of endothelium (58% control). Genistein's inactive congener daidzein (5 x 10(-6) M) did not reduce maximal contraction to 5-HT in carotid arteries but did shift the 5-HT concentration response curve 3-fold to the right. Tyrphostin 23 (5 x 10(-5) M), another tyrosine kinase inhibitor, decreased the potency of 5-HT 4-fold and reduced the maximal contraction to 5-HT in the carotid artery (10% control). Contractions induced by phorbol-12,13-dibutyrate (10(-9) to 10(-5) M) were not reduced or shifted by either tyrosine kinase inhibitor, indicating that phorbolester-sensitive protein kinase C isoforms were not affected. KCl-induced contraction was shifted 2-fold and the maximum significantly inhibited by tyrphostin 23 (38.6% control) but not genistein or daidzein, indicating that tyrphostin 23 but not genistein may inhibit voltage-gated calcium channels to reduce contractility. Western blot analysis using antiphosphotyrosine antibody confirmed that 5-HT produced a time- and concentration-dependent increase in the phosphotyrosine immunoreactivity of a 42-kD protein in cultured aortic smooth muscle cells. Lysate immunoprecipitation with an antimitogen-activated-protein (MAP)-kinase antibody indicated that the 42-kD protein was most likely a MAP kinase. 5-HT (10(-5) M) stimulated contraction and increased antiphosphotyrosine immunoreactivity in whole aorta mounted in tissue baths. Importantly, aortic contraction to 5-HT was shifted (5-fold rightward) and reduced (69% control) by genistein but not daidzein. These findings demonstrate that (1) tyrosine kinase activation may partially mediate contractility to 5-HT in arterial smooth muscle, (2) tyrphostin 23 is somewhat nonselective and (3) 5-HT stimulates tyrosine kinase as documented by increased tyrosyl phosphorylation of proteins in cultured aortic smooth muscle cells and aortic tissue in active contraction of 5-HT. These findings have significant implications not only in understanding a novel pathway of 5-HT signal transduction but also in vascular diseases in which growth and/or contractility to 5-HT is increased (e.g. hypertension, atherosclerosis).     

Routine chest radiographs following central venous recatheterization over a wire are not justified

Under in vitro conditions N-alpha-tosyl L-arginine methyl ester (TAME) induced a concentration dependent contractile response on ileal strips with EC50 of 4.3 x 10(-5) M as compared to acetylcholine which induced sustainable contractions with EC50 of 3.2 x 10(-6) M. The present study is the first to demonstrate that TAME is a potent constrictor of non-airway smooth muscle.     

Effect of nitroprusside on smooth muscle and adrenergic nerve terminals in isolated blood vessels

Experiments were designed to assess the mode of action of nitroprusside on isolated blood vessels and its relative potency on venous and arterial smooth muscle. Strips from dog blood vessels were mounted in an organ bath for isometric tension recording. Sodium nitroprusside (10(-5) M) depressed the contraction of saphenous vein strips caused by electric stimulation, tyramine, K+, Ba++, norepinephrine and acetylcholine. The depression of the norepinephrine-induced contractions also occurred in a Ca++- free medium and when Ca++ influx was inhibited by verapamil. Nitroprusside reduced the frequency of the spontaneous contractions of strips of portal-mesenteric veins. It depressed the contraction caused by norepinephrine in tibial artery strips more than in saphenous vein strips. Saphenous vein strips were incubated with (3H)norepinephrine and mounted for superfusion and isometric tension recording. Sodium nitroprusside (10(-5) M) had no effect on the basal efflux of 3H compounds. During electric stimulation, it did not change the output of (3H)norepinephrine but increased the outflow of deaminated and O-methylated metabolites. Thus sodium nitroprusside 1) has a direct effect on the smooth muscle cells which is independent of Ca++ influx, 2) depresses contractions of different types of vascular smooth muscle and 3) does not inhibit the release of norepinephrine from the nerve endings.     

Differences in familial segregation of FEV1 between asthmatic and nonasthmatic families. Role of a maternal component

To study the roles of phosphodiesterase (PDE) 4 in the human airways, we examined the effect of the novel PDE4 inhibitor T-440 in the isolated human bronchus. T-440 inhibited PDE4 extracted from human bronchial smooth muscle. IC50 values for the effect of T-440, rolipram (a PDE4 inhibitor) and theophylline on PDE4 activity of the bronchial tissues were 0.08 microM, 2 microM and > 100 microM, respectively. T-440 (10(-6) M to 10(-5) M) and aminophylline (3.3 x 10(-5) M) significantly reversed the 10(-5) M histamine-induced contraction, the efficacy of 10(-6) M T-440 being almost the same as that of 3.3 x 10(-5) M aminophylline. T-440 (10(-6) M to 10(-5) M) and aminophylline (3.3 x 10(-5) M) significantly reversed the 10(-4) M ACh-induced contraction. But their reversal effects on the ACh-induced contraction were weaker than those on the histamine-induced contraction. T-440 (10(-5) M) significantly reversed the contraction induced by allergen in passively sensitized bronchi. The efficacy of the reversal effect of T-440 (10(-5) M) was significantly higher than that of aminophylline (10(-5) M). T-440 and aminophylline significantly relaxed the basal tension, but pretreatment with T-440 or aminophylline did not significantly prevent histamine- or ACh-induced contraction. In contrast, both T-440 (10(-5) M) and aminophylline (3.3 x 10(-5) M) prevented the contraction induced by allergen, which suggests that PDE4 inhibitor inhibits the release of chemical mediators probably from bronchial mast cells in the allergic response. T-440 (10(-6) M to 10(-5) M) caused the accumulation of cAMP at the concentration that relaxed histamine-induced contraction. Thus selective PDE4 inhibitor is a candidate for the treatment of asthma.     

Mosaicism in trisomy 8: phenotype differences according to tissular repartition of normal and trisomic clones

The functional role of non-adrenergic non-cholinergic (NANC) nerves in the autonomic control of the male mini-pig bladder neck was investigated in the present study. Electrical stimulation of muscle strips from male mini-pig bladder neck showed biphasic response with initial phasic contraction followed by post-contractile relaxation. Electrical stimulation in the presence of four autonomic blockers (atropine 10(-6) M, propanolol 10(-6) M, phentolamine 10(-6) M) showed suppression of 68 +/- 15% of the contractile response (P < 0.05, n = 8) but no significant change in the relaxation response. Alpha-chymotrypsin 2 U/ml, L-NG-monomethyl-L-arginine acetate (a nitric oxide synthetase inhibitor) 10(-4) M, 8-phenylthlophylline (a P1-purinoceptor antagonist) 10(-6) M, and pyridoxal-phosphate-6-azophenyl-2', 4'-disulphoric acid tetrasodium salt (a P2Y-purinoceptor antagonist) 3 x 10(-5) M did not alter the NANC response significantly. On the other hand, reactive blue-2 (a P2Y-purinoceptor antagonist) 3 x 10(-5) significantly reduced the relaxation by 79 +/- 9%. The result suggested that the P2Y-purinoceptor is involved in the electrically induced NANC post-contractile relaxation of the mini-pig bladder neck smooth muscle.     

The use of controlled-release oxycodone for the treatment of chronic cancer pain: a randomized, double-blind study

1. We have studied the effects of muscarinic cholinoceptor agonists and subtype-preferring antagonists on the isometric contraction of smooth muscle strips from dog prostate. 2. Acetylcholine and carbachol induced contraction of prostate strips from the peripheral zone, ('the capsule'). Bethanechol contracted the tissue but not at lower doses. McN-A-343 and oxotremorine-M showed the same effects. 3. Blocking alpha- and beta-adrenoceptors with phentolamine and propranolol, respectively, did not modify carbachol-induced contractions. 4. The nicotinic receptor blocker, hexamethonium (10(-6)-10(-4) M) did not affect the contractile response evoked by a single dose of carbachol (10(-5) M), whilst the muscarinic receptor antagonist, atropine (10(-11)-10(-9) M), inhibited it in a competitive manner. 5. The muscarinic M1 (pirenzepine), M2 [AF-DX 116, himbacine (M2/M4) and methoctramine], M3 (HHSID and f-F-HHSID), and putative M4 (tropicamide) antagonists reduced significantly the carbachol-induced contractions. The pIC50 values were: atropine (10.01) > himbacine (8.3) > methoctramine (7.85) > AF-DX 116 (7.60) > HHSID (7.21) > p-F-HHSID (7.10) > pirenzepine (7.30) > tropicamide (7.00). 6. The antagonist profile indicates that an predominant M2 receptor subtype could mediate the muscarinic contraction in the canine prostate.     

Motilin in human milk: identification and stability during digestion

The presence of motilin in human milk and the influence of human milk on the degradation of [125I][Nle13] porcine motilin by gastric and duodenal fluids were investigated. Milk and plasma samples were collected from 14 mothers, and motilin was measured by radioimmunoassay. Plasma levels were 416 +/- 37 pg/mL. In 8 defatted samples the motilin level was 105 +/- 14 pg/mL, in the six others levels were above 1000 pg/mL but dilution curves were non-linear. After solid-phase extraction milk levels were 108 +/- 21 pg/mL in 13 samples, in 1 sample the dilution curve was still non-linear. The stability of motilin after ingestion was studied in vitro by incubating [121I][Nle13] porcine motilin with gastric and intestinal juices obtained from newborns (10 times diluted). Incubations were performed at 37 degrees C at pH 1.8, 3.2 and 5.8 for the gastric fluid and at pH 7.4 for the duodenal fluid. After different times of intervals (5, 10, 20 and 30 minutes) intact motilin was precipitated with trichloroacetic acid and the radioactivity of the supernatant was determined. Motilin was rapidly degraded by gastric juice. The breakdown was greatest at pH 3.2 (74% after 30 minutes) and lowest at pH 5.8 (29%), the pH after milk feeding in neonates. Degradation by intestinal juice at pH 7.4 was also very rapid (77% after 30 minutes). Human milk and BSA inhibited partially the gastric digestion at pH 3.2 (17 and 29%, respectively). Digestion by intestinal juice was not affected by human milk and BSA. These results suggest that digestion of motilin in the stomach may be sufficiently retarded by human milk in the newborn to exert a biological role.     

Mechanism of rat uterine smooth muscle contraction induced by endothelin-1

1. Endothelin (ET)-1 has been demonstrated to cause contraction of uterine smooth muscle. We investigated the role of ET receptor subtypes (ETA and ETB receptors) in ET-1-induced contraction of rat uterine smooth muscle by using the ETA receptor antagonist BQ-123 and the ETB receptor agonist BQ-3020. 2. ET-1 caused a contraction with superimposed oscillations of the rat isolated uterus suspended in Krebs-Ringer solution; both the amplitude of contraction as well as the oscillation frequency increased in a dose-dependent manner (10(-11)-10(-7)M). 3. BQ-123 (10(-6)M) markedly shifted the dose-response curve of ET-1 for both contractile effects and oscillation frequency to the right. 4. BQ-3020 (10(-11)-3 x 10(-7) M) did not cause uterine contraction; neither did it affect the dose-response curve of ET-1 for either the contractile effect or the increase in oscillation frequency. Thus, stimulation of ETB receptors is not involved in these responses. 5. The present findings suggest that ET-1-induced contractile responses and the increase in oscillation frequency in rat uterine smooth muscle is mediated through ETA receptors, and that ETB receptors play no role in these responses.     

Cisapride stimulates contraction of idiopathic megacolonic smooth muscle in cats

We have previously shown that cisapride, a substituted piperidinyl benzamide, stimulates contraction of healthy feline colonic smooth muscle. The purpose of the present investigation was to determine the effect of cisapride on feline idiopathic megacolonic smooth muscle function. Longitudinal smooth muscle strips from ascending and descending colon were obtained from cats with idiopathic megacolon, suspended in a 1.5 mM Ca(2+)-HEPES buffer solution (37 degrees C, 100% O2, pH 7.4), attached to isometric force transducers, and stretched to optimal muscle length (Lo). Control responses were obtained at each muscle site with acetylcholine (10(-8) to 10(-4) M), substance P (10(-11) to 10(-7) M), or potassium chloride (10 to 80 mM). Muscles were then stimulated with cumulative (10(-9) to 10(-6) M) doses of cisapride in the absence or presence of tetrodotoxin (10(-6) M) and atropine (10(-6) M), or in a 0 calcium HEPES buffer solution. In cats with idiopathic megacolon, cisapride stimulated contractions of longitudinal smooth muscle from both the ascending and the descending colon. Cisapride-induced contractions were similar in magnitude to those induced by substance P and acetylcholine in the ascending colon, but were less than those observed in the descending colon. Cisapride-induced contractions in megacolonic smooth muscle were only partially inhibited by tetrodotoxin and atropine, but were virtually abolished by removal of extracellular calcium. We concluded that cisapride-induced contractions of feline megacolonic smooth muscle are largely smooth muscle mediated and dependent on influx of extracellular calcium. Cisapride-induced contractions in megacolonic smooth muscle are only partially dependent on enteric cholinergic nerves. Thus, cisapride may be useful in the treatment of cats with idiopathic megacolon.     

Mechanism of nitric oxide-induced contraction in the rat isolated small intestine

1. The contractile response to nitric oxide (NO) in ral ileal myenteric plexus-longitudinal muscle strips was pharmacologically analysed. 2. NO (10(-7) M) induced only contraction while 10(-6) M NO induced contraction followed by relaxation. Methylene blue (up to 10(-4) M) did not affect the NO-induced contractions but significantly reduced the relaxation evoked by 10(-6) M NO. Administration of 8-bromo-cyclic GMP (10(-6)-10(-4) M) only induced relaxation. 3. Sodium nitroprusside (SNP; 10(-7)-10(-5) M) induced concentration-dependent contractions per se; the contractile response to NO, administered within 10 min after SNP, was concentration-dependently reduced. The guanosine 3':5'-cyclic monophosphate (cyclic GMP) content of the tissues was not increased during contractions with 10(-8) M NO and 10(-6) M SNP; it was increased by a factor of 2 during contraction with 10(-7) M NO, and by a factor of 12 during relaxation with 3 x 10(-6) M NO. 4. The NO-induced contractions were not affected by ryanodine (3 x 10(-5) M) but were concentration-dependently reduced by nifedipine (10(-8)-10(-7) M) and apamin (3 x 10(-9)-3 x 10(-8) M). 5. These results suggest that cyclic GMP is not involved in the NO-induced contraction in the rat small intestine. The NO-induced contraction is related to extracellular Ca2+ influx through L-type Ca2+ channels, that might be activated in response to the closure of Ca(2+)-dependent K+ channels.     

Action of substance P and interaction of calcitonin gene-related peptide and substance P on the cat antral circular muscle

The actions of substance P (SP) and calcitonin gene-related peptide (CGRP) and their interaction were examined in vitro in the feline antrum and colon. Circular muscle contraction was seen in the antrum to both peptides, but only to SP in the proximal colon. Antral contraction was enhanced when both peptides were given together. This interaction was inhibited by tetrodotoxin or atropine. SP acted at the antrum via a smooth muscle neurokinin receptor which is not a (NK)-1 receptor. SP binding was displaced by neurokinin A but not by the NK-1 receptor antagonist, CP-96345. The colonic response was inhibited by CP-96345. Immunohistochemistry revealed SP-like immunoreactivity (SP-LI) in fibers in the antral myenteric plexus and circular muscle, while CGRP-like immunoreactivity (CGRP-LI) was seen in the myenteric plexus only, without co-localization. These studies supported the hypothesis that SP acted via the NK-2 receptor at the feline circular muscle in the antrum to induce contraction and at the NK-1 receptor in the proximal colon. CGRP enhanced the effect of SP via a cholinergic pathway.     

Ketamine relaxes airway smooth muscle contracted by endothelin

Endothelins (ETs) are synthesized not only in vascular endothelial cells but also in airway epithelial cells. Increased ET-1 has been demonstrated in bronchial epithelium of asthmatic patients, and, in severe asthma attacks, ET-1 increases in plasma and bronchoalveolar lavage fluid. In this study, we investigated whether ketamine (KET) relaxes ET-induced tracheal contractions. Female guinea pigs were killed with an overdose of pentobarbital. The trachea was removed and cut spirally into two strips that were mounted in an organ bath filled with Krebs-bicarbonate buffer. The response of each strip to 10(-7) M carbachol was taken as 100% contraction to which the response to ET was referred. The contribution of the epithelium to the relaxant effect of KET was studied in denuded tracheae or in the presence of 5 x 10(-5) M indomethacin. ET-1 (3 x 10(-8) M) induced contractions that were 76 +/- 3% of those induced by carbachol. KET reversed the response to ET-1 in a dose-dependent fashion. Similarly, ET-2 (3 x 10(-8) M) induced contractions that were 74 +/- 5% of those induced by carbachol, and KET also reversed this response in a dose-dependent manner. In epithelium-denuded strips, ET-1 induced contractions that were 104 +/- 3% of those induced by carbachol, and KET still reversed this response. The tonic phase of the response to ET-1 was equal (100 +/- 6%) to the response to carbachol, and KET did not affect it significantly. In the presence of ryanodine, KET reduced the ET-1-induced contraction from 67 +/- 2% to 36 +/- 3.%, P < 0.01. In the presence of nicardipine, KET also inhibited the ET-1-induced contraction. We conclude that KET relaxes the tracheal smooth muscle contracted by ETs via a mechanism that is independent of the tracheal epithelium. The relaxant effect of KET on the ET-induced contraction of the trachealis muscle is not dependent upon blockade of 1) sarcolemma influx of Ca2+ through the dihydropyridine Ca2+ channel or 2) the release of intracellular Ca2+ through the ryanodine-sensitive intracellular Ca2+ channel. It is likely that the action of KET relaxing ET-induced tracheal contractions is at some point of the inositol 1,4,5-trisphosphate signaling pathway.     

Dengue virus infection: epidemiology, pathogenesis, clinical presentation, diagnosis, and prevention

OBJECTIVES: To investigate whether the isolated urinary bladder spontaneously releases substance P (SP) or bradykinin (BK), which can act as potent mediators of pain and inflammation of the urinary bladder, and whether peptidase inhibitors enhance peptide release. MATERIALS AND METHODS: Urinary bladder segments (2 x 10 x 0.8-1 mm) were isolated from guinea pigs and studied in vitro; tissue contraction was assessed using force-displacement transducers and the release of peptides by specific enzyme immunoassays. RESULTS: In the absence of any exogenous agonists, the inhibition of neutral endopeptidase and angiotensin-converting enzyme by phosphoramidon and captopril, respectively, increased the frequency and magnitude of spontaneous motility of isolated bladder strips. Phosphoramidon increased the net release of SP-like immunoreactivity (SP-LI) and captopril increased the net release of SP-LI and BK-LI, concomitant with contraction. Peptide-LI was recovered primarily from bladder mucosa and to a lesser degree from detrusor smooth muscle. Similarly, peptidase inhibitors primarily affected the bladder mucosa; phosphoramidon induced a fourfold increase in SP-LI and captopril induced a significant increase of SP-LI and BK-LI from the mucosa. Tissues contracted in response to peptidase inhibitors in the presence of atropine and indomethacin, but contraction was reduced significantly by in vitro capsaicin desensitization or removal of bladder mucosa. BK stimulated SP-LI release from mucosa but not detrusor. SP stimulated increased BK-LI release from mucosa and detrusor. CONCLUSIONS: These findings indicate the basal release of peptide-like immunoreactivity by isolated bladder and further support the concept that peptidases located in the bladder mucosa are important in terminating the effects of endogenous peptides.     

The role of the N-methyl-D-aspartic acid receptor in the relaxant effect of ketamine on tracheal smooth muscle

Ketamine and magnesium (Mg2+), well known bronchodilators, have been used to treat patients with status asthmaticus. Both can block the N-methyl-D-aspartic acid (NMDA) receptor. NMDA receptors exist in the airway, and their activation seems to be linked to the release actions of sensory neuropeptides resulting in increased airway tone. We sought to determine whether ketamine relaxes the guinea pig trachea contracted by histamine by blocking the NMDA receptor. Female guinea pigs (250-400 g) were killed with an overdose of pentobarbital. The trachea was removed and cut spirally into strips 3 mm wide and 15 mm long. The strips were mounted in a 10-mL organ bath filled with Tyrode's solution bubbled through with 95% O2/5% CO2 at 37 degrees C. Strip contractions were measured isometrically with a force displacement transducer. We then studied the effect of NMDA receptor antagonists on histamine-induced tracheal contraction. In this protocol, we examined the effect of ketamine, Mg2+, zinc (Zn2+), or MK-801 (a noncompetitive NMDA receptor blocker) on strips contracted by 10(-5) M histamine. After full contraction was attained, ketamine (0.5-1.5 mM), MgSO4 (2-8 mM), ZnCl2(0.2-0.8 mM), or MK-801 (1.5-6 x 10(-5) M) was added, and the strip tension was measured again. We also studied the effect of NMDA on the relaxation by ketamine. After full contraction by 10(-5) M histamine, 0.5-1.5 mM KET was added alone or in combination with 0.1 mM NMDA, and the strip tension was measured again. Finally, we measured the effect of MK-801 on the relaxant effect of ketamine. After full contraction by 10(-5) M histamine, 0.5-2 mM ketamine was added alone or in combination with 0.75 or 1.5 x 10(-5) M MK-801, and the strip tension was measured again. All NMDA receptor antagonists tested reversed the tracheal contraction induced by histamine in a dose-dependent manner. However, neither the agonist NMDA nor the noncompetitive receptor blocker MK-801 affected tracheal relaxation induced by ketamine. We conclude that ketamine relaxes the tracheal smooth muscle contracted by histamine through a mechanism independent of NMDA receptors. The decreased bronchomotor tone induced by ketamine is probably due to interference with a Ca2+-requiring step necessary to maintain the contraction caused by histamine. IMPLICATIONS: Stimulation of the N-methyl-D-aspartic acid (NMDA) receptor in the airway results in airway constriction. The bronchodilator ketamine blocks the NMDA receptor. However, ketamine relaxes the guinea pig trachea contracted by histamine through a mechanism independent of the NMDA receptor.     

The effects of heparin on intrauterine arteries of the human non-pregnant uterus: II. The analysis of the route of action

OBJECTIVE: Our purpose was to elucidate the mechanism of heparin action on smooth muscle of small intramyometrial arteries. MATERIAL AND METHOD: Material was obtained, contractility and calcium concentration were measured as previously described. Calcium influx to the vascular cells was also measured. RESULTS: Heparin did not change basal tension of the arterial strips. The strips precontracted by K(+)-depolarisation were relaxed by heparin at concentration: 200-1000 UI/mL. The maximal relaxation never exceeded 66 +/- 5.1%. Heparin (200 UI/mL) decreased the free calcium concentration in Tyrode solution to 0.8 mM. Such a lowering of the free calcium concentration diminished vascular contractile reactions. Heparin did not disturb the basal calcium influx into vascular cells but significantly decreased that which was stimulated by K+ depolarisation. 120 min treatment with heparin resulted in reducing the arterial response to 3 x 10(-8) M vasopressin recorded in Ca-free conditions. CONCLUSIONS: 1. Our results suggest that heparin, in vitro, effects the vascular smooth muscle contractions by influence on both extracellular free calcium concentration and Ca2+ influx into cytoplasm. 2. Relaxant action of heparine, on the vascular smooth muscle, is activated by additives present in commercial preparation.     

Early discharge after open appendicectomy

This study was undertaken to characterize the interaction of porcine galanin (Gal) and some of its analogues with their receptors on rat gastric fundus muscle strips. Gal, galantide (M15) and Gal(1-14)-[Abu8]SCY-I evoked concentration-dependent contractions of gastric smooth muscle strips. Reproducible effects were observed in concentrations of 1-300, 3-1000 and 100-3000 nM, respectively. Specific EC50 for the contractile effect equalled 13.70 and 187 nM. Hill's coefficient for Gal is 1.03 indicating an interaction of one Gal molecule with one receptor, fulfilling the criteria of classical receptor theory. For M15 and Gal(1-14)-[Abu8]SCY-I Hill's coefficients are different from 1, namely 0.73 and 1.56, pointing out that the principle of interaction of one drug molecule with one receptor may not apply. The contraction induced by 300 nM of Gal was not significantly modified by tachyphylaxis to substance P (SP). On the contrary the introduction of tachyphylaxis to SP decreased the contractile effects of M15 and Gal(1-14)-[Abu8]SCY-I by about 57.7 +/- 3% and 39.6 +/- 5%, respectively. The findings suggest that contractile actions of M15 and Gal(1-14)-[Abu8]SCY-I are probably not only due to their agonist activities at Gal receptors but may result from a subsequent stimulation of receptors for SP or release of endogenous SP.     

Lysophosphatidylcholine potentiates vascular contractile responses by enhancing vasoconstrictor-induced increase in cytosolic free Ca2+ in rat aorta

We investigated the effects of palmitoyl-L-alpha-lysophosphatidylcholine on the contractile responses of the endothelium-denuded rat aorta to high K+, noradrenaline, UK14,304 (5-bromo-6-[2-imidazolin-2-ylamino]-quinoxaline) (a selective alpha2 adrenoceptor agonist) and phorbol 12-myristate 13-acetate (PMA). Lysophosphatidylcholine at concentrations from 10(-6) M to 10(-4) M did not contract aortic strips. However, lysophosphatidylcholine strongly potentiated the UK14,304-induced contraction. High K+ - and PMA-induced contractions were also potentiated. In contrast, the noradrenaline-induced contraction was only slightly potentiated by 10(-5) M lysophosphatidylcholine. In fura PE-3-loaded aortic strips, lysophosphatidylcholine (10(-5) M) markedly augmented the increase in both cytosolic free Ca2+ ([Ca2+]i) and contractile tension induced by UK14,304, high K+ and PMA. Nicardipine (10(-7) M) and 10(-6) M Ro-31-8220 (?1-[3-(amidinothio)propyl-1H-indoyl-3-yl]-3-(1-methyl-1H-++ +indoyl-3-yl)-maleimide-methane sulfate) strongly inhibited the increase in [Ca2+]i and contractile tension induced by UK14,304 and in the presence of these inhibitors, the enhancing effects of lysophosphatidylcholine were attenuated. However, the enhancing effect on high K+ -induced contraction was not affected by Ro-31-8220. These results suggest that lysophosphatidylcholine may cause an augmentation of the increase in [Ca2+]i induced by UK14,304 which response is depend on protein kinase C activation and in this way potentiate contractile responses in the rat aorta. Protein kinase C independent mechanisms may also be involved in the enhancing effect of lysophosphatidylcholine on smooth muscle contraction.