Search results for "Phentolamine"
showing 10 items of 23 documents
Characterization of 5-hydroxytryptamine release from isolated rabbit and rat trachea: the role of neuroendocrine epithelial cells and mast cells
1995
Rabbit or rat isolated tracheae were incubated in vitro, and the release of 5-hydroxytryptamine (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) was determined by HPLC with electrochemical detection. Release of 5-HT from rabbit tracheae could be evoked by the calcium ionophore A 23187 and, in a calcium-dependent manner, by depolarizing concentrations of potassium (45 mmol/l), but not by the mast cell degranulating drug compound 48/80. High potassium- and A 23187-evoked release of 5-HT was markedly higher from tracheae of newborn compared to adult rabbits. In rabbit tracheae, mechanical removal of the mucosa resulted in 80-90% reduction in tissue 5-HT and in a similar reduction …
Tetrodotoxin-dependent effects of menthol on mouse gastric motor function.
2013
Menthol, the main active constituent of peppermint oil, exerts gut spasmolytic effects, although its mechanism of action remains unclear. We investigated the effects of menthol on gastric emptying and spontaneous- or evoked- mechanical activity of whole murine stomach. Gastric emptying was calculated after i.p. administration of menthol (50mg/Kg). Responses induced by menthol on gastric intraluminal pressure and evoked-cholinergic contractions were analyzed in vitro. Menthol decreased the gastric emptying rate. In vitro, menthol (0.3-30 mM) produced a concentration-dependent relaxation of whole stomach, that was significantly reduced by tetrodotoxin or ω-conotoxin GVIA. The gastric relaxant…
Contribution of both ?- and ?-adrenoceptors to the inotropic effects of catecholamines in the rabbit heart
1992
The functional role of alpha-adrenoceptors was investigated in different parts of the rabbit heart. Phenylephrine (PE) caused a marked increase in force of contraction (Fc) and a prolongation of the action potential (AP) in preparations from the left atrium and the right ventricle. The response was less pronounced in the right atrium and in the left ventricle, whereas APs of spontaneously beating sinoatrial preparations remained completely unchanged. Phentolamine as well as the diesters phorbol 12,13 dibutyrate (PDBu) or 12-O-tetradecanoyl-phorbol-13-acetate (TPA) eliminated the effects of PE. The contribution of alpha-adrenoceptors to the effects of adrenaline (Adr) and noradrenaline (NA) …
Increase by ?-adrenolytic drugs of acetylcholine release evoked by field stimulation of the guinea-pig ileum
1979
The release of acetylcholine evoked by field stimulation of the guinea-pig ileum (3 Hz) is increased by yohimbine and tolazoline but not affected by phentolamine. It is proposed that yohimbine and tolazoline by blocking alpha-adrenoceptors of the cholinergic nerves abolish the inhibition caused by endogenous noradrenaline, and thus facilitate the output of acetylcholine.
Evidence for the neuronal origin of immunoreactive interleukin-1 beta released by rat hypothalamic explants.
1996
In this study, we have investigated the release of immunoreactive interleukin-1 beta (irIL-1 beta) from the rat hypothalamus in vitro. It was found that (1) tissue explants release sizable amounts of irIL-1 beta (ranging from 0.43 to 0.52 pg/mg of wet tissue) in 20 min incubations; (2) basal release in significantly increased by depolarization induced with 56 mM KCl; (3) K(+)-induced irIL-1 beta release is inhibited by the specific blocker of N-type calcium channels, omega-conotoxin, and by verapamil, but not by nifedipine; (4) K(+)-induced release is also inhibited by the Na+ channel blockers tetrodotoxin and lidocaine; (5) irIL-1 beta release is significantly increased by noradrenalin; su…
Autoinhibition of noradrenaline release from the rat heart as a function of the biophase concentration. Effects of exogenous alpha-adrenoceptor agoni…
1984
1. Rat isolated perfused hearts with the right sympathetic nerves intact were loaded with 3H-(-)-noradrenaline. The nerves were stimulated with trains of 180 pulses at 3 Hz and at 10 min intervals. The overflow of 3H-noradrenaline and 3H-metabolites was determined by liquid scintillation spectrometry. 2. Clonidine (IC50 17 nM), oxymetazoline (IC50 63 nM), and α-methylnoradrenaline (apparent IC50 35 nM, determined in the presence of cocaine and propranolol) decreased the stimulation-evoked overflow of 3H-noradrenaline by 26, 49, and 78%, respectively, but not methoxamine up to 100 μM (propranolol present). Oxymetazoline and α-methyl-noradrenaline did not cause desensitization of the presynap…
Depolarization-induced influx of sodium in response to phenylephrine in rat atrial heart muscle.
1991
1. The effects of alpha 1-adrenoceptor stimulation on transmembrane potential, currents and ion fluxes were investigated in multicellular preparations and/or single cells obtained from the left atrium of rat hearts. 2. In multicellular preparations, phenylephrine caused a concentration-dependent positive inotropic effect, an increase in action potential duration, and a decrease in resting potential; the effects were antagonized by phentolamine. 3. In the presence of phenylephrine (100 mumol/1), two levels of resting potential were observed when the preparations were, alternately, electrically stimulated or kept at rest (-74 +/- 1 mV during activity and -62 +/- 4 mV at rest; mean +/- S.E.M.;…
Pharmacological analysis of the responsiveness of guinea-pig lung parenchymal strip to dopamine
1984
Abstract Responses to dopamine were examined in the guinea-pig isolated lung parenchymal strip. Complete cumulative concentration-response curves to dopamine exhibited a biphasic pattern with a small initial contraction at concentrations below 10(-5) M followed by a dose-dependent relaxation at higher concentrations. Phentolamine (10(-5) M) completely abolished the contractile component and enhanced sensitivity and maximal relaxation to dopamine. In the presence of phentolamine, propranolol antagonized the dopamine-induced relaxation (pA2 = 8.54 +/- 0.07). In the presence of propranolol (10(-6) M), dopamine produced a dose-related contraction displaced to the right by phentolamine. Incubati…
Evidence that depletion of internal calcium stores sensitive to noradrenaline elicits a contractile response dependent on extracellular calcium in ra…
1993
1. Noradrenaline 1 microM induced a contractile response in rat isolated aorta in the presence or in the absence of extracellular Ca2+ with depletion of intracellular Ca2+ stores. Thereafter, during incubation in the presence of Ca2+, an increase in the resting tone was observed. Such a contractile response did not occur after exposure to caffeine or 5-hydroxytryptamine. 2. This increase in tension was inhibited in a concentration-dependent manner by alpha-adrenoceptor antagonists (prazosin, phentolamine and yohimbine), the non-specific relaxing compound, papaverine and by the Ca(2+)-entry blocker, nifedipine. Therefore, this contractile process is related to depletion of Ca2+ stores sensit…
Alpha 2-receptor-mediated inhibition of intraluminal release of gastric somatostatin in anaesthetized rats.
1992
Alino, S. F., Garcia, D. & Uvnas-Moberg, K. 1992. Alpha2-receptor-mediated inhibition of intraluminal release of gastric somatostatin in anaesthetized rats. Acta Physiol Scand144, 233–238. Received 22 February 1991, accepted 11 October 1991. ISSN 00014772. Department of Pharmacology and Pharmaceutics, University of Valencia, Valencia, Spain, Department of Cell Biology and Morphology Science, University of Pais Vasco, Leioa, Spain and Department of Pharmacology, Karolinska Institute, Stockholm, Sweden. The aim of the present study was to investigate how the sympathetic nervous system affects the vagally induced intragastric release of somatostatin and gastrin. Experiments were performed on a…