Stimulation of pulmonary vagal C-fibers by trans-4-methyl-ß-nitrostyrene induces bradycardiac and depressor reflex in rats: Role of vanilloid TRPV1 receptors.

Previously, we showed that the synthetic nitroderivative trans-4-methyl-ß-nitrostyrene (T4MeN) induced vasorelaxant effects in rat isolated aortic rings. Here, we investigated the mechanisms underlying the cardiovascular effects of T4MeN in normotensive rats. In pentobarbital-anesthetized rats, intravenous (i.v.) injection of T4MeN (0.03-0.5 mg/kg) induced a rapid (onset time of 1-2 s) and dose-dependent bradycardia and hypotension. These cardiovascular responses to T4MeN were abolished by bilateral cervical vagotomy or selective blockade of neural conduction of vagal C-fiber afferents by perineural treatment of both cervical vagus nerves with capsaicin. Hypotension and bradycardia were also recorded when T4MeN was directly injected in the right, but not into the left ventricle. Furthermore, they were significantly reduced by i.v. pretreatment with capsazepine but remained unaltered by ondansetron or suramin. In conscious rats, the dose-dependent hypotension and bradycardia evoked by T4MeN were abolished by i.v. methylatropine pretreatment. In conclusion, bradycardiac and depressor responses induced by T4MeN has a vago-vagal reflex origin resulting from the vagal pulmonary afferents stimulation. The transduction mechanism seems to involve the activation of vanilloid TRPV1, but not purinergic (P2X) or 5-HT3 receptors located on vagal pulmonary sensory nerves.

Trans-4-methoxy-ß-nitrostyrene relaxes rat thoracic aorta through a sGC-dependent pathway.

1-Nitro-2-phenylethene (NPe) induces a more potent vasorelaxant effect in rat aorta than its structural analog 1-nitro-2-phenylethane, but mediated through a different mechanism, independent of soluble guanylate cyclase (sGC) stimulation. We hypothesized that introducing an electron donor into the aromatic moiety might stabilize NPe, enhancing its potency and/or interaction with sGC. Therefore, trans-4-methoxy-ß-nitrostyrene (T4MN) was synthesized, and mechanisms underlying its vasorelaxant effects were studied in rat aortic ring preparations. In endothelium-intact preparations, T4MN fully relaxed contractions induced by phenylephrine (PHE) with a potency similar to that of its parent drug, NPe. This vasorelaxant effect that was unchanged by endothelium removal, pretreatment with L-NAME, indomethacin, or MDL-12,330A, but was significantly reduced by tetraethylammonium, 4-aminopyridine, methyl blue, or ODQ. Under Ca2+-free conditions, T4MN did not alter contractions evoked by caffeine, but significantly reduced, in an ODQ-preventable manner, those induced by either PHE or extracellular Ca2+ restoration following depletion of intracellular Ca2+ stores in thapsigargin-treated aortic preparations. Under the same conditions, T4MN also reduced contractions induced by protein kinase C activator phorbol-12,13-dibutyrate with a potency similar to that evoked by this nitroderivative against PHE-induced contractions. In conclusion, T4MN induces potent vasorelaxation in rat aorta by stimulating the sGC-cGMP pathway through a NO-independent mechanism. Introduction of a methoxy group into the aromatic moiety apparently stabilizes NPe, thereby enhancing its interaction with sGC.

Mechanism of the vasorelaxant effect induced by trans-4-methyl-ß-nitrostyrene, a synthetic nitroderivative, in rat thoracic aorta.

Mechanisms underlying the vasorelaxant effects of trans-4-methyl-ß-nitrostyrene (T4MeN) were studied in rat aortic rings. In endothelium-intact preparations, T4MeN fully and similarly relaxed contractions induced by phenylephrine (PHE) (IC50  = 61.41 [35.40-87.42] µmol/L) and KCl (IC50  = 83.50 [56.63-110.50] µmol/L). The vasorelaxant effect of T4MeN was unchanged by endothelium removal, pretreatment with L-NAME, indomethacin, tetraethylammonium, ODQ or MDL-12,330A. Under Ca2+ -free conditions, T4MeN significantly reduced with a similar potency: (i) phasic contractions induced by PHE, but not by caffeine; (ii) contractions due to CaCl2 in aortic preparations stimulated with PHE (in the presence of verapamil) or high KCl; (iii) contractions evoked by the restoration of external Ca2+ levels after depletion of intracellular Ca2+ stores in the presence of thapsigargin. In contrast, T4MeN was more potent at inhibiting contractions evoked by the tyrosine phosphatase inhibitor, sodium orthovanadate, than those induced by the activator of PKC, phorbol-12,13-dibutyrate. These results suggest that T4MeN induces an endothelium- independent vasorelaxation that appears to occur intracellularly through the inhibition of contractions that are independent of Ca2+ influx from the extracellular milieu but involve phosphorylation of tyrosine residues.

trans-Caryophyllene, a natural sesquiterpene, causes tracheal smooth muscle relaxation through blockade of voltage-dependent Ca²âº channels.

trans-Caryophyllene is a major component in the essential oils of various species of medicinal plants used in popular medicine in Brazil. It belongs to the chemical class of the sesquiterpenes and has been the subject of a number of studies. Here, we evaluated the effects of this compound in airway smooth muscle. The biological activities of trans-caryophyllene were examined in isolated bath organs to investigate the effect in basal tonus. Electromechanical and pharmacomechanical couplings were evaluated through the responses to K⁺ depolarization and exposure to acetylcholine (ACh), respectively. Isolated cells of rat tracheal smooth muscle were used to investigate trans-caryophyllene effects on voltage-dependent Ca²âº channels by using the whole-cell voltage-clamp configuration of the patch-clamp technique. trans-Caryophyllene showed more efficiency in the blockade of electromechanical excitation-contraction coupling while it has only minor inhibitory effect on pharmacomechanical coupling. Epithelium removal does not modify tracheal smooth muscle response elicited by trans-caryophyllene in the pharmacomechanical coupling. Under Ca²âº-free conditions, pre-exposure to trans-caryophyllene did not reduce the contraction induced by ACh in isolated rat tracheal smooth muscle, regardless of the presence of intact epithelium. In the whole-cell configuration, trans-caryophyllene (3 mM), inhibited the inward Ba²âº current (I(Ba)) to approximately 50% of control levels. Altogether, our results demonstrate that trans-caryophyllene has anti-spasmodic activity on rat tracheal smooth muscle which could be explained, at least in part, by the voltage-dependent Ca²âº channels blockade.