ABSTRACT
Effects of Substance P on spontaneous contractions of the circular muscle of the flexure region of guinea pig colon were studied by mechanical tension recording. Substance P (3 nM-10 nM) produced tonic contraction associated with phasic activities but the contraction was found stronger at higher concentration. Verapamil (3 microM), a voltage dependent L-type Ca(2+) channel blocker completely blocked the spontaneous activities and also Substance P induced contraction. These results suggest that Substance P produce contraction by Ca(2+) influx and the Ca(2+) influx occurs by activating verapamil sensitive Ca(2+) channel.
Subject(s)
Animals , Calcium Channel Blockers/pharmacology , Colon/drug effects , Female , Guinea Pigs , Isotonic Solutions , Male , Models, Animal , Muscle Contraction/drug effects , Muscle, Smooth/drug effects , Receptors, Tachykinin/drug effects , Substance P/pharmacology , Time Factors , Verapamil/pharmacologyABSTRACT
<p><b>AIM</b>To investigate the influence and the mechanism of SK on the contractility of cultured cardiomyocytes of rats.</p><p><b>METHODS</b>The primary cultured single myocardial cell was treated with SK and the contraction frequency and size of cardiomyocyte were determined by a computer image analysis system. At the same time the effects of propranolol (a beta receptor antagonist), phentolamine (a alpha receptor antagonist), DSP (a tachykinin receptor antagonist) on the action of SK were investigated.</p><p><b>RESULTS</b>SK increased contractive extend of the cardiomyocyte, in which a dose-response relationship of SK at 1.78 x 10(-8) - 1.78 x 10(-5) mol/L exists. But the frequency of contraction did not change, pretreatment with propranolol, phentolamine had no action on the effect of SK, but DSP markedly attenuated the effects of SK.</p><p><b>CONCLUSION</b>SK may directly enhance the contractility of single cardiomyocyte, which may be related with the tachykinin receptor.</p>
Subject(s)
Animals , Rats , Animals, Newborn , Benzylamines , Pharmacology , Cells, Cultured , Dose-Response Relationship, Drug , Myocardial Contraction , Myocytes, Cardiac , Physiology , Neurokinin A , Pharmacology , Phentolamine , Pharmacology , Propranolol , Pharmacology , Rats, Wistar , Receptors, TachykininABSTRACT
BACKGROUND: Asthma is an inflammatory disease because there are many inflammatory changes in the asthmatic airways. Axon reflex mechanisms may be involved in the pathogenesis of asthma. Sensory neuropeptides are involved in this inflammation, which is defined as neurogenic inflammation. Substance p, neurokinin A, and neurokinin B may be main neuropeptides of neurogenic inflammation in airways. These tachykinins act on neurokinin recptors. Three types of neurokinin receptors, such as NK1, NK2, and NK3, are currently recognized, at which substance p,neurokinin A, and neurokinin B may be the most relvant natural agonist of neurogenic inflammation in airways. The receptor subtypes present in several tissues have been characterized on the basis of differential sensitivity to substance p, neurokinin A, and neurokinin B. Plasma extravasation and vasodilation are induced by substance p more potently than by neurokinin A, indicating NK1 receptors on endothelial cells mediate the response. But airway contraction is induced by neurokinin A more potently than by substance P, indicating the NK2 receptors in airway smooth muscles. These receptors are used to evaulate the pathogenesis of brochial asthma. FK224 was identified from the fermentation products of Streptomyces violaceoniger. FK224 is a dual antagonist of both NK1 and NK2 recptors. PURPOSE: For a study of pathogenesis of bronchial asthma, the effect of FK224 on plasma extravasation induced by vagal NANC electrical stimulation was evaluated in rat airway. METHOD: Male Sprague-Dawley rats weighing 180~450gm were anesthetized by i.p. injection of urethane. Plasma extravasation was induced by electrical stimulation of cervical vagus NANC nerves with 5Hz, 1mA, and 5V for 2 minutes(NANC2 group) and for sham operation without nerve stimulation(control group). To evaluate the effect of FK224 on plasma extravasation in neurogenic inflammation, FK224(lmg/kg, Fujisawa Pharmaceutical Co., dissolved in dimethylsul- phoxide; DMSO, Sigma Co.) was injected 1 min before nerve stimulation(FK224 group). To assess plasma exudation, Evans blue dye(20mg/kg,dissolved in saline) was used as a plasma marker and was injected before nerve stimulation. After removal of intravascular dye, the evans blue dye in the tissue was extracted in formamide(37degreesC, 24h) and quantified spectrophotometrically by measuring dye absorbance at 629nm wavelength. Tissue dye content was expressed as ng of dye per mg of wet weight tissue. The amount of plasma extravasation was measured on the part of airways in each groups. RESULTS: 1) Vagus nerve(NANC) stimulation significantly increased plasma leakage in trachea, main bronchus, and peripheral bronchus compared with control group, 14.1 +/-1.6 to 49.7+/-2.5, 17.5 +2.0 to 38.7 +/-2.8, and 12.7+/-2.2 to 19.1 +/-1.6ng of dye per mg of tissue(mean +/- SE), respectively(p0.05) 2) FK224 had significant inhibitory effect upon vagal nerve stimulation-induced airway plasma leakage in any airway tissues of rat,such as trachea, main bronchus, and peripheral bronchus compared with vagus nerve stimulation group, 49%, 58%, and 70%, respectively(p<0.05). Inhibitory effect of FK224 on airway plasma leakage in neurogenic inflammation was revealed the more significant in peripheral bronchus, but no significant in lung parenchyma. CONCLUSION: These results suggest that FK224 is a selective NK receptor antagonist which effectively inhibits airway plasma leakage induced by the endogenous neurotransmitters relased by neurogenic inflammation in rat airway. Tachykinin receptor antagonists may be useful in the treatment of brochial asthma.