Corticotropin-releasing hormone mimics stress-induced colonic epithelial pathophysiology in the rat.
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We examined the effect of stress on colonic epithelial physiology, the role of corticotropin-releasing hormone (CRH), and the pathways involved. Rats were restrained or injected intraperitoneally with CRH or saline. Colonic segments were mounted in Ussing chambers, in which ion secretion and permeability (conductance and probe fluxes) were measured. To test the pathways involved in CRH-induced changes, rats were pretreated with hexamethonium, atropine, bretylium, doxantrazole, alpha-helical CRH-(9-41) (all intraperitoneally), or aminoglutethimide (subcutaneously). Restraint stress increased colonic ion secretion and permeability to ions, the bacterial peptide FMLP, and horseradish peroxidase (HRP). These changes were prevented by alpha-helical CRH-(9-41) and mimicked by CRH (50 microgram/kg). CRH-induced changes in ion secretion were abolished by alpha-helical CRH-(9-41), hexamethonium, atropine, or doxantrazole. CRH-stimulated conductance was significantly inhibited by alpha-helical CRH-(9-41), hexamethonium, bretylium, or doxantrazole. CRH-induced enhancement of HRP flux was significantly reduced by all drugs but aminoglutethimide. Peripheral CRH reproduced stress-induced colonic epithelial pathophysiology via cholinergic and adrenergic nerves and mast cells. Modulation of stress responses may be relevant to the management of colonic disorders. (+info)
Preventing ventricular fibrillation by flattening cardiac restitution.
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Ventricular fibrillation is the leading cause of sudden cardiac death. In fibrillation, fragmented electrical waves meander erratically through the heart muscle, creating disordered and ineffective contraction. Theoretical and computer studies, as well as recent experimental evidence, have suggested that fibrillation is created and sustained by the property of restitution of the cardiac action potential duration (that is, its dependence on the previous diastolic interval). The restitution hypothesis states that steeply sloped restitution curves create unstable wave propagation that results in wave break, the event that is necessary for fibrillation. Here we present experimental evidence supporting this idea. In particular, we identify the action of the drug bretylium as a prototype for the future development of effective restitution-based antifibrillatory agents. We show that bretylium acts in accord with the restitution hypothesis: by flattening restitution curves, it prevents wave break and thus prevents fibrillation. It even converts existing fibrillation, either to a periodic state (ventricular tachycardia, which is much more easily controlled) or to quiescent healthy tissue. (+info)
Effects of forearm bier block with bretylium on the hemodynamic and metabolic responses to handgrip.
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We tested the hypothesis that a reduction in sympathetic tone to exercising forearm muscle would increase blood flow, reduce muscle acidosis, and attenuate reflex responses. Subjects performed a progressive, four-stage rhythmic handgrip protocol before and after forearm bier block with bretylium as forearm blood flow (Doppler) and metabolic (venous effluent metabolite concentration and (31)P-NMR indexes) and autonomic reflex responses (heart rate, blood pressure, and sympathetic nerve traffic) were measured. Bretylium inhibits the release of norepinephrine at the neurovascular junction. Bier block increased blood flow as well as oxygen consumption in the exercising forearm (P < 0.03 and P < 0.02, respectively). However, despite this increase in flow, venous K(+) release and H(+) release were both increased during exercise (P < 0.002 for both indexes). Additionally, minimal muscle pH measured during the first minute of recovery with NMR was lower after bier block (6.41 +/- 0.08 vs. 6.20 +/- 0.06; P < 0.036, simple effects). Meanwhile, reflex effects were unaffected by the bretylium bier block. The results support the conclusion that sympathetic stimulation to muscle during exercise not only limits muscle blood flow but also appears to limit anaerobiosis and H(+) release, presumably through a preferential recruitment of oxidative fibers. (+info)
Ciliary ganglion stimulation. II. Neurogenic, intraocular pathway for excitatory effects on aqueous humor production and outflow.
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Data obtained suggest that preganglionic stimulation of the ciliary ganglion produces an increase of aqueous humor formation and of facility of outflow "C" through the following neurogenic pathway: (1) the preganglionic fibers synapse in the ciliary ganglion as evidenced by depression of the response with nicotine applied topically to the ganglion. (2) The impulse proceeds to the equivalent of an intraocular interneuron which can be blocked by low concentrations of atropine and has been previously identified as being an E-2 receptor site. (3) From the interneuron, activity is ultimately exerted without further synapse on alpha-adrenergic receptors through the release of norepinephrine from the neuronal terminals. The adrenergic mechanism of action is supported by the inhibition of the responses by phenoxybenzamine, bretylium, and guanethidine. Constriction of efferent ciliary process blood vessels by neuron-released norepinephrine seems to be the end effect responsible for the increased production of aqueous humor. The site of the end response to increase "C" is unclear. (+info)
Effect of destruction of the posterior pituitary on the diuresis from left atrial receptors.
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1. In anaesthetized dogs, stimulation of atrial receptors after destruction of the pituitary gland results in a diuresis. This response was not abolished by the administration of bretylium tosylate and was also observed in a surgically denervated kidney. 2. The diuresis is qualitatively similar to that observed in anaesthetized dogs with intact pituitary glands. 3. It is concluded that the diuresis which results from stimulation of the left atrial receptors is mediated by a blood-borne agent which is not the antidiuretic hormone. (+info)
Acute cold exposure induces vagally mediated Fos expression in gastric myenteric neurons in conscious rats.
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Acute cold exposure-induced activation of gastric myenteric neurons in conscious rats was examined on longitudinal muscle-myenteric plexus whole mount preparations. Few Fos-immunoreactive (IR) cells (<1/ganglion) were observed in 24-h fasted rats semirestrained at room temperature. Cold exposure (4 degrees C) for 1-3 h induced a time-related increase of Fos-IR cells in corpus and antral myenteric ganglia with a maximal plateau response (17 +/- 3 and 18 +/- 3 cells/ganglion, respectively) occurring at 2 h. Gastric vagotomy partly prevented, whereas bilateral cervical vagotomy completely abolished, Fos expression in the myenteric cells induced by cold exposure (2 h). Hexamethonium (20 mg/kg) also prevented 3-h cold exposure-induced myenteric Fos expression by 76-80%, whereas atropine or bretylium had no effect. Double labeling revealed that cold (3 h)-induced Fos-IR myenteric cells were mainly neurons, including a substantial number of choline acetyltransferase-containing neurons and most NADPH-diaphorase-positive neurons. These results indicate that acute cold exposure activates cholinergic as well as nitrergic neurons in the gastric myenteric ganglia through vagal nicotinic pathways in conscious rats. (+info)
Influence of cocaine and sodium on bretylium uptake by reserpine-treated guinea-pig left atrium.
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1 The effects of cocaine and sodium on bretylium uptake into sympathetic nerve terminals were investigated in the reserpine-treated guinea-pig left atrium. The ability of bretylium pretreatment to increase the retention of noradrenaline was used as an index of bretylium uptake. Such increased retention has been assessed both by direct measurement and by the ability of tyramine to produce an inotropic response. 2 The restoration of the response to tyramine after incubation with noradrenaline was abolished when the atrium was pretreated with bretylium in the presence of cocaine. When bretylium was added before cocaine, or when alpha-methyl-noradrenaline (not a substrate for monoamine oxidase) was used for incubation, the responses to tyramine were restored in the normal way. 3 Bretylium greatly enhanced the retention of [3-H]-noradrenaline; when bretylium was added in the presence of cocaine, [3-H]-noradrenaline retention was severely impaired. 4 Pretreatment with bretylium in a low-sodium (25 mM) or sodium-free medium significantly decreased the retention of [3-H]-noradrenaline, as compared with the control. 5 Potassium deprivation did not modify the enhanced retention of [3-H]-noradrenaline induced by bretylium pretreatment. 6 Bretylium was released from the nerve terminals by exposure of the preparation to a sodium-free medium or to a solution containing calcium 50 mM, leading to a considerable decrease in [3-H]-noradrenaline retention. 7 The results are consistent with the view that both cocaine and sodium deprivation block the uptake of bretylium by the adrenergic nerve terminals, and that bretylium is probably taken up by a mechanism similar to or identical with the uptake system for noradrenaline and other amines. (+info)
Studies of uptake of the bretylium analogue, iodobenzyltrimethylammonium iodide, by non-primate, monkey and human hearts.
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Uptake of (+/-)-[3H]-noradrenaline, [14C]-bretylium and [125I]-o-iodobenzyltrimethylammonium iodide (RIBA) by rat heart was studied by the Langendorff technique. All three compounds showed significant uptake. 2 Corticosterone and 17-beta-oestradiol inhibited the uptake of all three compounds by rat heart, a finding consistent with extraneuronal uptake (uptake2). 3 [131I]-RIBA was injected intravenously into pigs and monkeys (M. speciosus). Myocardial samples taken from pigs killed 1 and 2 h after injection showed significant uptake. No significant uptake was found in myocardial samples of monkeys killed 10 min, 2 h and 24 h, respectively, after injection. 4 Four normal human volunteers received [125I]-RIBA intravenously and the image of the precordial area was followed by means of scintillation camera for the first 4 h after injection. In two of the subjects, the scintigrams were repeated at 22 and 23 h after injection, respectively. No evidence of myocardial uptake was observed. 5 These results suggest the possibility that man and at least one other primate species may differ from lower species with regard to uptake. (+info)