Mechanisms underlying the neurokinin A-induced contraction of the pregnant rat myometrium

1. Using fura-PE3 fluorimetry and alpha-toxin permeabilization, the characteristics of the contractile responses to neurokinin A (NKA) were determined in the pregnant rat myometrium. 2. NKA induced contractions in rat myometrium in a concentration-dependent manner. There were no significant differences in the maximum contractions and EC(50) values between the pregnant and non-pregnant myometrium, however, the contraction of only the former was greatly enhanced in the presence of phosphoramidon (PPAD), an endopeptidase inhibitor. 3. In the pregnant myometrium, NKA induced sustained increases in [Ca(2+)](i) and tension in normal physiological saline solution, while only small transient increases in [Ca(2+)](i) and tension were observed in Ca(2+)-free solution. 4. Both diltiazem (10 microM) and SK-F 96365 (10 microM) significantly inhibited the NKA-induced elevations of [Ca(2+)](i) and tension. The effects were additive when these drugs were used together. 5. NKA induced a significant leftward shift of the [Ca(2+)](i)-tension curve obtained by changing the external Ca(2+) (0 - 2.5 mM) during depolarization with high K(+) solution. This Ca(2+)-sensitizing effect by NKA was also observed in the alpha-toxin permeabilized myometrium. 5. These results indicated that in the pregnant rat myometrium: (1) the responsiveness to NKA increased, although it was masked by the increase in the endopeptidase activity; (2) NKA induced contractions of the myometrium by increasing both [Ca(2+)](i) and the myofilament Ca(2+) sensitivity and (3) The NKA-induced [Ca(2+)](i) elevation was partly due to the intracellular Ca(2+) release and mainly due to the Ca(2+) influx, which was thought to be through both voltage dependent calcium channels and non-specification channels.     

Mechanisms underlying the vecuronium-induced tetanic fade in the isolated rat muscle

The cellular mechanisms underlying the effects of vecuronium on the tetanic contraction were studied in vitro with a combination of myographic and electrophysiologic techniques. We used the isolated sciatic nerve extensor digitorum longus muscle preparation of the rat. Indirect twitches were evoked at 0.1 Hz pulses and tetani at 50 Hz pulses. Trains of end-plate potentials were generated at 50 Hz. The electrophysiological variables used in the analysis of the end-plate potentials were: amplitude, tetanic run-down, quantal size and quantal content. The myographic study demonstrated that vecuronium at 0.4 microM caused tetanic fade, but left the twitch unaffected. Regarding electrophysiology, vecuronium (0.4 microM) decreased the amplitude of end-plate potentials and increased their tetanic run-down. These changes were due to significant reductions in both the quantal content of the end-plate potentials and the quantal size. It is concluded that vecuronium has both pre- and postsynaptic effects at the neuromuscular junction, and that it induces fade of the tetanic contraction via a summation of these effects.     

Effect of endopeptidase-24.11 inhibitors and C-ANP receptor ligand on responses evoked in arterioles of rat cremaster muscle by atrial natriuretic peptide.

1. The present study examined the effect of exogenous atrial natriuretric peptide (ANP), alone or in presence of inhibitors of the two major mechanisms for clearing ANP, metabolism by neutral endopeptidase-24.11 (NEP) and internalization by C-ANP receptors, on arteriolar responses using intravital microscopy on the rat cremaster muscle after intravenous or topical administration of the peptide. 2. Topical application of ANP (3 x 10(-10) to 3 x 10(-8) M) produced a gradual increase in arteriolar diameter. NEP inhibitors, thiorphan (30 mg kg-1, i.v.), kelatorphan (10 mg kg-1, i.v.) and retrothiorphan (25 mg kg-1, i.v.) alone, did not significantly affect vascular tone but caused significant potentiation of the arteriolar responses to topically applied ANP. 3. When given as an i.v. bolus, ANP dilates skeletal arterioles at a high dose (20 micrograms kg-1). At a lower dose (10 micrograms kg-2), ANP alone or with retrothiorphan or the C-ANP receptor ligand C-ANP (4-23) did not produce any arteriolar responses, while after the combined administration of the two inhibitors, an increase in arteriolar diameter was induced. 4. These results indicate that low doses of topically applied ANP dilate rat cremaster arterioles and that the vasodilator responses can be potentiated by NEP inhibition. When given as an i.v. bolus, a high dose of ANP can also dilate skeletal arterioles. However at a lower dose the rapid metabolism of the peptide prevents it from producing its action.     

Effects of dihydroergotamine methanesulfonate on the microcirculation of the rat cremaster muscle

Effects of dihydroergotamine on the microcirculation of the rat cremaster muscle were investigated microscopically using colour photographic technique. 1. Dihydroergotamine 10(-4) g/ml constricted arterioles of the rat cremaster. 2. Dihydroergotamine 10(-4) g/ml produced a significant contraction of venules. 3. Dihydroergotamine 10(-4) g/ml markedly inhibited the contractile response of noradrenaline 10(-6) g/ml on arterioles of the rat cremaster. The results suggest that dihydroergotamine has an appreciable vasoconstrictive action, especially upon venules, and that dihydroergotamine also has an adrenergic alpha-receptor blocking action. By means of highly sensitive negative colour film we obtained a satisfactory photograph of the rat cremaster's circulation.     

Mechanisms of hydroxyl radical-induced contraction of rat aorta

The present study was designed to investigate the effects of hydroxyl radicals (*OH), generated via the Fe2+-mediated Fenton reaction, on isolated rat aortic rings with and without endothelium. In the absence of any vasoactive agent, generation of *OH alone elicited an endothelium-independent contraction in rat aortic rings in a concentration-dependent manner. Hydroxyl radical-induced contractions of denuded rat aortic rings appeared, however, to be slightly stronger than those on intact rat aortic rings. The contractile responses to *OH were neither reversible nor reproducible in the same ring; even small concentrations of *OH radicals resulted in tachyphylaxis. Removal of extracellular calcium ions (Ca2+) or buffering intracellular Ca2+ with 10 microM acetyl methyl ester of bis(o-aminophenoxy) ethane-N,N,N',N',-tetraacetic acid (BAPTA-AM) significantly attenuated the contractile actions of *OH radicals. The presence of 1 microM staurosporine, 1 microM bisindolylmaleimide I, 1 microM G?6976 [inhibitor of protein kinase C (PKC)], 2 microM PD-980592 (inhibitor of ERK), 10 microM genistein, and 1 microM wortmannin significantly inhibited the contractions induced by *OH. Proadifen (10 microM), on the other hand, significantly potentiated the hydroxyl radical-induced contractions. Exposure of primary cultured aortic smooth muscle cells to *OH produced significant, rapid rises of intracellular free Ca2+ ([Ca2+]i). Several, specific antagonists of possible endogenously formed vasoconstrictors did not inhibit or attenuate either hydroxyl radical-induced contractions or the elevation of [Ca2+]i. Our new results suggest that hydroxyl radical-triggered contractions on rat aortic rings are Ca2+-dependent. Several intracellular signal transduction systems seem to play some role in hydroxyl radical-induced vasoconstriction of rat aortic rings.     

Cross talk between receptors mediating contraction and relaxation in the arterioles but not the dilator muscle of the rat iris.

1. Sympathetic nerve stimulation causes contraction of the dilator muscle and the large arterioles of the iris via the activation of alpha 1B-adrenoceptors. We have investigated whether increases in adenosine 3': 5'-cyclic monophosphate (cyclic AMP) and the activation of receptors in these tissues can modulate these nerve-mediated contractions. 2. Increasing intracellular cyclic AMP with dibutyryl cyclic AMP (1 mM), forskolin (50 microM) or isobutylmethylxanthine (100 microM) produced relaxation of both the dilator and the arterioles, abolished the nerve-mediated constriction of the arterioles, but potentiated the nerve-mediated contraction of the iris dilator. 3. Pretreatment of the preparations with cholera toxin, to activate Gs permanently, caused a dilatation of the arterioles and abolished the nerve-mediated constriction but had no effect on the dilator muscle. 4. The beta-adrenoceptor agonist, isoprenaline (1 microM), the adenosine-A1,-A2 agonist, N-ethylcarboxamidoadenosine NECA (100 nM), in the presence of the A1-selective antagonist, 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX, 10 nM), and calcitonin gene-related peptide (CGRP, 10 nM) all separately caused a dilatation of the arterioles and abolished the nerve-mediated constriction, while only isoprenaline (1 microM) produced an effect on the dilator, i.e. a relaxation but a potentiation of the nerve-mediated contraction. These results suggest the presence of at least 3 types of receptor linked to Gs and an increase in cyclic AMP in the arterioles, i.e. beta-adrenoceptor, adenosine-A2 and CGRP, but only 1 Gs-linked receptor, i.e. beta-adrenoceptors, on the dilator muscle cells.2+ '     

Mechanisms underlying diabetes enhancement of endothelin-1-induced contraction in rabbit basilar artery

The influence of alloxan-induced diabetes on the reactivity of rabbit basilar artery to endothelin-1 was examined. Endothelin-1 induced concentration-dependent contraction of basilar arteries that was higher in diabetic than in control rabbits. Endothelium removal produced a higher enhancement of the endothelin-1-induced contraction in control than in diabetic rabbits. N(G)-nitro-L-arginine (L-NOArg) enhanced the maximal contraction induced by endothelin-1 in control rabbits and potentiated this response in diabetic rabbits. Endothelin ETA receptor antagonist, cyclo(D-Asp-Pro-D-Val-Leu-D-Trp) (BQ-123), inhibited endothelin-1-induced contraction in both rabbit groups. Endothelin ETB receptor antagonist, 2,6-Dimethylpiperidinecarbonyl-gamma-Methyl-Leu-Nin-(Methoxycarbonyl)-D-Trp-D-Nle (BQ-788), enhanced endothelin-1-induced contraction in control rabbits and decreased the potency of endothelin-1 in diabetic rabbits. Sodium nitroprusside-induced relaxation of basilar arteries was lower in diabetic than in control rabbits. These results suggest that mechanisms underlying rabbit basilar artery hyperreactivity to endothelin-1 include decreased endothelial modulation of endothelin-1-induced contraction, with impaired endothelial endothelin ETB receptor activity; decreased sensitivity to nitric oxide (NO) in vascular smooth muscle; and enhanced participation of muscular endothelin ETA and ETB receptors.     

Effects of intra-arterial administration of prostaglandin E1 on rat cremaster muscle microcirculation

In plastic and reconstructive surgery, postoperative drug therapy with prostaglandin E1 (PGE1) has been widely used to prevent flap necrosis and to extend flap surviving area. In the present study, we assessed the effects of intra-arterial administration of PGE1 on microcirculation. The left cremaster muscle of male Wistar rats were used to measure microcirculatory hemodynamic parameters. The values of internal vessel diameter and erythrocyte velocity were measured by using the confocal laser-scanning microscope (CLSM) system and fluorescent dyes. The blood flow rate was calculated from measured internal vessel diameter and erythrocyte velocity. Internal vessel diameter and flowing erythrocytes were satisfactorily visualized by using the CLSM system. The blood flow rate of arteriole, venule and capillary were dose dependently increased by the intra-arterial administration of PGE1 from the minimum dose of 0.01 ng/kg/min. It is suggested that the intra-arterial administration of PGE1 is a more effective way of postoperative drug therapy than intravenous injection for flap surgery.     

Mechanisms underlying contraction and relaxation induced by nerve stimulation in monkey uterine arteries

We investigated the mechanisms of contractile and relaxant responses to nerve stimulation by electrical pulses and nicotine in isolated monkey uterine artery strips denuded of the endothelium. In the strips contracted with prostaglandin F(2alpha), transmural electrical stimulation (5 Hz, 40 s) produced a contraction which was partially attenuated by prazosin and abolished or reversed to a relaxation by additional treatment with alpha,beta-methylene ATP. The relaxation was abolished by N(G)-nitro-L-arginine (L-NA) and restored by L-arginine but not by D-arginine. Atropine, D-NA, aminophylline and suramin, an inhibitor of P(2Y) purinoceptors, were without effect. The neurogenic relaxation was abolished by 1H-(1,2, 4)oxadiazolo(4,3)quinoxalin-1-one (ODQ), an inhibitor of soluble guanylate cyclase. Nicotine (10(-4) mol/l) elicited contraction or relaxation of uterine arteries; the contraction was reversed by combined treatment with prazosin and alpha,beta-methylene ATP. Nicotine-induced relaxations were abolished by L-NA and restored by L-arginine. The relaxation induced by exogenously applied NO (acidified NaNO(2) solution) was not influenced by L-NA but abolished by ODQ. It is concluded that contractions induced by nerve stimulation are mediated by norepinephrine and ATP liberated from sympathetic nerves that stimulate alpha(1)-adrenoceptors and P(2x) purinoceptors, respectively. The neurogenic relaxation seems to be mediated exclusively by nitric oxide synthesized from L-arginine in perivascular nerves that activates guanylate cyclase and produces cyclic GMP in smooth muscle.     

The effect of oxytocin on blood vessels of cremaster muscle of the rat.

Oxytocin administered intravenously to the anaesthetized rat produced dilatation of the blood vessels of the cremaster muscle at concentrations ranging from 2.5 times 10-minus 11 to 2.5 times 10-minus 9 M. When applied topically to the exposed vessels it produced constriction at concentrations ranging from 2.5 times 10-minus 12 to 5.0 times 10-minus 8 M. Oxytocin was thus similar to adrenaline in eliciting opposite effects when applied to the serosa or to the intima of skeletal muscle blood vessels.     

Mechanisms involved in UTP-induced contraction in isolated rat aorta

The mechanisms of UTP-induced contractions in the rat aorta strips were studied. These were only partially inhibited in a Ca(2+)-free medium or by incubation with verapamil or nifedipine. Successive challenges did not decrease the magnitude of the contraction in the absence of external Ca(2+). Quin 2(acetoxymethyl) ester (Quin 2AM), 8-(N,N-diethylamino)octyl 3,4,5-trimetoxybenzoate (TMB-8), thapsigargin and ryanodine inhibited these contractions. The participation of protein kinase C is also very likely, since downregulation by the phorbol 12,13 dibutyrate (PDB) decreased UTP-induced contraction, and staurosporine and 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) antagonized UTP-induced contractions and relaxed UTP-induced tonic contractions. Therefore, different pools of intracellular Ca(2+) and protein kinase C seem to participate in UTP-induced contraction and in the mechanisms of maintenance in a Ca(2+)-free medium.     

Receptor signaling mechanisms underlying muscarinic agonist-evoked contraction in guinea-pig ileal longitudinal smooth muscle

1 In guinea-pig ileal longitudinal muscle, muscarinic partial agonists, 4-(N-[3-chlorophenyl]-carbomoyloxy)-2-butynyl-trimethylammonium (McN-A343) and pilocarpine, each produced parallel increases in tension and cytosolic Ca(2+) concentration ([Ca(2+)]c) with a higher EC(50) than that of the full agonist carbachol. The maximum response of [Ca(2+)]c or tension was not much different among the three agonists. The Ca(2+) channel blocker nicardipine markedly inhibited the effects of all three agonists 2 The contractile response to any agonist was antagonized in a competitive manner by M(2) receptor selective antagonists (N,N'-bis[6-[[(2-methoyphenyl)methyl]amino]hexyl]-1,8-octanediamine tetrahydrochloride and 11-[[2-[(diethlamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido[2,3-b][1,4] benzodiazepine-6-one), and the apparent order of M(2) antagonist sensitivity was McN-A343>pilocarpine>carbachol. M(3) receptor selective antagonists, 1,1-dimethyl-4-diphenylacetoxypiperidinium iodide and darifenacin, both severely depressed the maximum response for McN-A343, while darifenacin had a similar action in the case of pilocarpine. Both M(3) antagonists behaved in a competitive manner in the case of the carbachol response. 3 McN-A343 failed to release Ca(2+) from the intracellular stores, and the Ca(2+)-releasing action of pilocarpine was very weak compared with that of carbachol. All three agonists were capable of increasing Ca(2+) sensitivity of the contractile proteins. 4 McN-A343 rarely produced membrane depolarization, but always accelerated electrical spike discharge. Pilocarpine effect was more often accompanied by membrane depolarization, as was usually seen using carbachol. 5 The results suggest that muscarinic agonist-evoked contractions result primarily from the integration of Ca(2+) entry associated with the increased spike discharge and myofilaments Ca(2+) sensitization, and that Ca(2+) store release may contribute to the contraction indirectly via potentiation of the electrical membrane responses. They may also support the idea that an interaction of M(2) and M(3) receptors plays a crucial role in mediating the contraction response.     

Mechanisms involved in the blocking effects of pimozide on smooth muscle contraction

Pimozide, a dopamine-receptor antagonist, shifted to the right the concentration-response curves (CRC) induced by (-)-noradrenaline in the isolated posterior mesenteric artery of the cat. Since this antagonism could be related to a blockade of vascular alpha-adrenoceptors, we compared the effects of pimozide (0.20 microM) with those of phentolamine (0.31 microM). The onset of the blockade by pimozide on the (-)-noradrenaline-induced contractions was slower when compared with that of phentolamine. In addition, the effects of pimozide did not reverse by washing while those of phentolamine did. Pimozide but not phentolamine inhibited the contractions elicited by potassium and it decreased the maximum responses of the curves. This effect was partially reversed by CaCl2 10.2 mM. Pimozide displaced the CRC induced by CaCl2 to a greater extent than phentolamine. Even if a blocking effect on alpha-adrenoceptors cannot be discarded, our results suggest that pimozide may interfere with calcium in the arterial smooth muscle. Furthermore, vascular smooth muscle seems to be more sensitive than non-vascular tissue to the action of pimozide.     

Mechanisms underlying endothelium-dependent flow increase in perfused rat mesenteric vascular bed

The isolated rat mesenteric vasculature was perfused at constant pressures of 40, 80 or 120 mm Hg and the change in flow rate was measured. In the presence of phenylephrine, treatment with 3-[(3-cholamidopropyl) dimethylammonio]-1-propane sulfonate (CHAPS) or N(G)-nitro-L-arginine (L-NA) significantly inhibited the pressure-dependent flow rate increase, but treatment with indomethacin or charybdotoxin plus apamin did not. Acetylcholine, bradykinin and ADP increased the flow rate, which had been markedly suppressed by CHAPS. At 80 mm Hg, the flow rate increase induced by these agonists was not affected by indomethacin plus L-NA, but was suppressed by subsequent treatment with charybdotoxin plus apamin. Changes in the perfusion pressure did not significantly affect the flow rate increases induced by the agonists. In conclusion, the opening of charybdotoxin plus apamin-sensitive Ca(2+)-dependent K(+) channels may be mainly involved in the endothelium-dependent flow rate increase induced by the agonists, whereas nitric oxide (NO) may be responsible for the endothelium-dependent, pressure-induced flow rate increase.     

Mechanisms underlying cancer-induced symptoms

In addition to the physical and emotional suffering induced by the diagnosis of cancer, patients are subjected to additional discomfort and suffering from symptoms induced by both the disease and its treatment. While an increasing amount of clinical and basic science research has focused on these issues, our understanding of the mechanisms underlying cancer-related symptoms remains incomplete. This article summarizes what is known about the mechanisms underlying the common symptoms of pain, cachexia, nausea and vomiting, dyspnea, fatigue and mood disorders, as well as the implications of these findings for therapeutic intervention.