Maternal Hyperglycemia Induces Autonomic Dysfunction and Heart Failure in Older Adult Offspring.

AIMS: Offspring exposed to an adverse fetal environment, such as gestational diabetes, may manifest increased susceptibility to several chronic diseases later in life. In the present study, the cardiovascular function of three different ages of offspring from diabetic rats was evaluated. METHODS AND RESULTS: Diabetes mellitus was induced in pregnant rats by a single dose of streptozotocin (50 mg/kg). The offspring from diabetic (OD) and control rats (OC) were evaluated at three different ages: 6, 12 or 18 months. In the corresponding OC groups, fasting glycemia, baseline mean arterial pressure, and sympathetic tonus increased in the OD rats at 12 (OD12) and 18 (OD18) months of age, while cardiac hypertrophy was observed in all OD groups. Cardiac function evaluation in vivo showed low left ventricular systolic pressure and+dP/dt in the OD18 rats, suggesting a systolic dysfunction. OD12 and OD18 groups showed high left ventricle end-diastolic pressure, suggesting a diastolic dysfunction. OD groups showed an age-related impairment of both baroreflex-mediated tachycardia and baroreflex-mediated bradycardia in OD12 and OD18 rats. In isolated hearts from OD18 rats, both inotropic and tachycardiac responses to increasing isoproterenol were significantly reduced compared to the corresponding OC group. CONCLUSION: These results suggest that gestational diabetes triggers the onset of hyperglycemia hypertension with impaired baroreflex sensitivity and heart failure in older age of offspring, representing important risk factors for death. Therefore, ensuring optimal glycemic control in diabetic pregnancy is important and serves as a key to preventing cardiovascular disease in the offspring in their older age.

The soluble guanylate cyclase stimulator, 1-nitro-2-phenylethane, reverses monocrotaline-induced pulmonary arterial hypertension in rats.

AIMS: We examined the effects of treatment with 1-nitro-2-phenylethane (NP), a novel soluble guanylate cyclase stimulator, on monocrotaline (MCT)-induced PAH in rats. MAIN METHODS: At day 0, male adult rats were injected with a single subcutaneous (s.c.) dose of monocrotaline (60 mg/kg). Control (CNT) rats received an equal volume of monocrotaline's vehicle only (s.c.). Four weeks later, MCT-treated rats were treated orally for 14 days with NP (50 mg/kg/day) (MCT-NP group) or its vehicle (Tween 2%) (MCT-V group). At the end of the treatment period and before invasive hemodynamic study, rats of all experimental groups were examined by echocardiography. KEY FINDINGS: With respect to CNT rats, MCT-V rats showed significant; (1) increases in pulmonary artery (PA) diameter, RV free wall thickness and end-diastolic RV area, and increase of Fulton index; (2) decreases in maximum pulmonary flow velocity, PA acceleration time (PAAT), PAAT/time of ejection ratio, and velocity-time integral; (3) increases in estimated mean pulmonary arterial pressure; (4) reduction of maximal relaxation to acetylcholine in aortic rings, and (5) increases in wall thickness of pulmonary arterioles. All these measured parameters were significantly reduced or even abolished by oral treatment with NP. SIGNIFICANCE: NP reversed endothelial dysfunction and pulmonary vascular remodeling, which in turn reduced ventricular hypertrophy. NP reduced pulmonary artery stiffness, normalized the pulmonary artery diameter and alleviated RV enlargement. Thus, NP may represent a new therapeutic or a complementary approach to treatment of PAH.

Soluble guanylate cyclase stimulator, trans-4-methoxy-ß-nitrostyrene, has a beneficial effect in monocrotaline-induced pulmonary arterial hypertension in rats.

The soluble guanylate cyclase (sGC)/GMPc pathway plays an important role in controlling pulmonary arterial hypertension (PAH). We investigated whether the novel sGC stimulator trans-4-methoxy-ß-nitrostyrene (T4MN), ameliorates monocrotaline (MCT)-induced PAH. At Day 0, rats were injected with MCT (60 mg/kg, s. c.). Control (CNT) rats received an equal volume of monocrotaline vehicle only (s.c.). Four weeks later, MCT-treated rats were orally treated for 14 days with T4MN (75 mg/kg/day) (MCT-T4MN group) or its vehicle (MCT-V group), and with sildenafil (SIL; 50 mg/kg) (MCT-SIL group). Compared to the CNT group, MCT treatment induced a significant increase in both the Fulton index and RV systolic pressure but significantly reduced the maximum relaxation induced by acetylcholine. Indeed, MCT treatment increased the wall thickness of small and larger pulmonary arterioles. Oral treatment with T4MN and SIL reduced the Fulton index and RV systolic pressure compared to the MCT-V group. Maximum relaxation induced by acetylcholine was significantly enhanced in MCT-SIL group. Both T4MN and SIL significantly reduced the enhanced wall thickness of small and larger pulmonary arterioles. Treatment with T4MN has a beneficial effect on PAH by reducing RV systolic pressure and consequently right ventricular hypertrophy, and by reducing pulmonary artery remodeling. T4MN may represent a new therapeutic or complementary approach for the treatment of PAH.

Vasodilatory action of trans-4-methoxy-ß-nitrostyrene in rat isolated pulmonary artery.

Trans-4-methoxy-ß-nitrostyrene (T4MN) induced more potent vasorelaxant effects in resistance arteries from hypertensive rats than its parent drug, ß-nitrostyrene 1-nitro-2-phenylethene (NPe). To better understand the influence of insertion of the electron-releasing methoxy group in the aromatic ring of NPe, we investigated vasorelaxant effects of T4MN in isolated pulmonary artery and compared them with those of NPe in view of the potential interest of T4MN in pulmonary arterial hypertension. T4MN and NPe both caused concentration-dependent vasorelaxation in pulmonary artery rings pre-contracted with either phenylephrine (1 µmol/L) or KCl (60 mmol/L), an effect unaffected by endothelium removal. In endothelium-intact preparations pre-contracted with phenylephrine, the vasorelaxant effect of T4MN was more potent than that of NPe. However, unlike NPe, this effect was significantly reduced following pretreatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10 µmol/L, a guanylate cyclase inhibitor) or tetraethylammonium (5 mmol/L, a potassium channel blocker). T4MN abolished the CaCl2 -induced contractions in pulmonary artery preparations stimulated with phenylephrine (PHE) under Ca2+ -free conditions in the presence of verapamil, to preferentially activate receptor-operated calcium channels. From these findings, we propose that T4MN evokes endothelium-independent vasorelaxant effects in isolated rat pulmonary artery, partially by inhibiting Ca2+ influx through L-type Ca2+ channels, as well as by activating soluble guanylate cyclase and potassium channels. The present results suggest the therapeutic potential of T4MN in treating pulmonary arterial hypertension.

Vasorelaxant effect of trans-4-chloro-ß-nitrostyrene, a synthetic nitroderivative, in rat thoracic aorta.

Previously, we showed that 1-nitro-2-phenylethene, a nitrostyrene derivative of 1-nitro-2-phenylethane, induced vasorelaxant effects in rat aorta preparations. Here, we studied mechanisms underlying the vasorelaxant effects of its structural analog, trans-4-chloro-ß-nitrostyrene (T4CN), in rat aortic rings. Increasing concentrations of T4CN (0.54-544.69 µm) fully and similarly relaxed contractions induced by phenylephrine (PHE, 1 µm) or KCl (60 mm) in endothelium-intact aortic rings with IC50 values of 66.74 [59.66-89.04] and 79.41 [39.92-158.01] µm, respectively. In both electromechanical and pharmacomechanical couplings, the vasorelaxant effects of T4CN remained unaltered by endothelium removal, as evidenced by the IC50 values (108.35 [56.49-207.78] and 65.92 [39.72-109.40] µm, respectively). Pretreatment of endothelium-intact preparations with L-NAME, ODQ, glibenclamide, or TEA did not change the vasorelaxant effect of T4CN. Under Ca2+ -free conditions, T4CN significantly reduced the phasic contractions induced by caffeine or PHE, as well as the contractions due to exogenous CaCl2 in aortic preparations stimulated with PHE (in the presence of verapamil). These results suggest that in rat aortic rings, T4CN induced vasorelaxation independently from the activation of soluble guanylate cyclase/cGMP pathway, an effect that may be related to the electrophilicity of the substituted chloro-nitrostyrene. This vasorelaxation seems to involve inhibition of both calcium influx from the extracellular milieu and calcium mobilization from intracellular stores mediated by IP3 receptors and by ryanodine-sensitive Ca2+ channels.

GQ-130, a novel analogue of thiazolidinedione, improves obesity-induced metabolic alterations in rats: Evidence for the involvement of PPARß/δ pathway.

The present investigation aimed to characterize the effect of a short-time treatment with a new thiazolidinedione (TZD) derivative, GQ-130, on metabolic alterations in rats fed a high-fat diet (HFD). We investigated whether metabolic alterations induced by GQ-130 were mediated though a mechanism that involves PPARß/δ transactivation. Potential binding and transactivation of PPARα, PPARß/δ or PPARγ by GQ-130 were examined through cell transactivation, 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence quenching assays and thermal shift assay. For in vivo experiments, male 8-week-old Wistar rats were divided into three groups fed for 6 weeks with: (a) a standard rat chow (14% fat) (control group), (b) a HFD (57.8% fat) alone (HFD group), or (c) a HFD associated with an oral treatment with GQ-130 (10 mg/kg/d) during the last week (HFD-GQ group). In 293T cells, unlike rosiglitazone, GQ-130 did not cause significant transactivation of PPARγ but was able to activate PPARß/δ by 153.9 folds in comparison with control values (DMSO). Surprisingly, ANS fluorescence quenching assay reveals that GQ-130 does not bind directly to PPARß/δ binding site, a finding that was further corroborated by thermal shift assay which evaluates the thermal stability of PPARß/δ in the presence of GQ-130. Compared to the control group, rats of the HFD group showed obesity, increased systolic blood pressure (SBP), insulin resistance, impaired glucose intolerance, hyperglycaemia, and dyslipidaemia. GQ-130 treatment abolished the increased SBP and improved all metabolic dysfunctions observed in the HFD group. Oral treatment with GQ-130 was effective in improving HFD-induced metabolic alterations probably through a mechanism that involves PPARß/δ activation.

Cardiovascular Effects of Trans-4-Methoxy-ß-Nitrostyrene in Spontaneously Hypertensive Rats: Comparison With Its Parent Drug ß-Nitrostyrene.

We previously reported that trans-4-methoxy-ß-nitrostyrene (T4MN) evoked higher vasorelaxant effects in small resistance arteries from spontaneously hypertensive rats (SHRs) in comparison with its parent drug, the ß-nitrostyrene 1-nitro-2-phenylethene (NPe). To further our knowledge of the influence of insertion of an electron-releasing group such as methoxy in the aromatic ring of NPe, we investigated the cardiovascular responses to intravenous (i.v.) injection of T4MN in SHRs and compared with those of NPe. In anesthetized SHRs, i.v. treatment with T4MN (0.03-0.5 mg/kg) and NPe (0.03-3 mg/kg) induced dose-dependent bradycardia and hypotension, which were biphasic (named phases 1 and 2). Magnitude of these responses was significantly higher for T4MN compared with NPe. Phase 1 cardiovascular responses to both T4MN (0.3 mg/kg) and NPe (3 mg/kg) were prevented by cervical bivagotomy or perineural treatment of both cervical vagus nerves with capsaicin, but was unchanged by i.v. pretreatment with capsazepine or ondansetron. After injection into the left ventricle, NPe and T4MN no longer evoked phase 1 responses. In conscious SHRs, NPe (3 mg/kg, i.v.), and T4MN (0.3 mg/kg, i.v.) evoked monophasic hypotensive and bradycardiac effects which were suppressed by i.v. pretreatment with methylatropine. It is concluded that i.v. administration of NPe and T4MN in SHRs induced a vago-vagal hypotensive and bradycardic reflex that did not involve the activation of vanilloid TRPV1 or 5-HT3 receptors located on vagal pulmonary sensory nerves. With respect to its parent drug, T4MN was more potent in inducing this reflex. Phase 2 hypotensive response to i.v. NPe and T4MN seems partially resulting from a direct vasodilatory action. It seems that insertion of a methoxy group into the aromatic ring stabilized NPe, which in turn increases its cardiovascular effects.

Endothelium-dependent and endothelium-independent effects of 1-nitro-2-propylbenzene on rat aorta.

A group of nitro compounds contains a benzene ring in a short aliphatic chain with the NO2 group, property that supposedly favors its vasodilator profile. In this study, we evaluated in isolated rat aorta the effects of 1-nitro-2-propylbenzene (NPB), a nitro compound containing the NO2 in the aromatic ring. In aorta precontracted with KCl, NPB (1-3000 µm) induced full endothelium-independent relaxation. In endothelium-intact preparations, phenylephrine-induced contractions were fully relaxed by NPB, effect unaltered by N(ω)-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). In the concentration range of 30-300 µm, NPB slightly but significantly potentiated the phenylephrine-induced contraction. Such potentiation was unaltered by the thromboxane-prostanoid receptor antagonist seratrodast, but was abolished by endothelium removal or by preincubation of endothelium-intact preparations with L-NAME, ODQ or by ruthenium red and HC-030031, blockers of subtype 1 of ankyrin transient receptor potential (TRPA1 ) channels. Verapamil exacerbated the potentiating effect of NPB. The potentiating effect was undetectable in preparations precontracted by 9,11-dideoxy-11α,9α-epoxymethanoprostaglandin F2α (U-46619). Relaxation was reduced by ruthenium red while it was enhanced by HC-030031. In conclusion, NPB has vasodilator properties but with a mechanism of action distinct from its analogues. Contrary to other nitro compounds, its relaxing effects did not involve recruitment of the guanylyl cyclase pathway. NPB has also endothelium-dependent potentiating properties on phenylephrine-induced contractions, a phenomenon that putatively required a role of endothelial TRPA1 channels. The present findings reinforce the notion that the functional group NO2 in the aliphatic chain of these nitro compounds determines favorably their vasodilator properties.

Chronic administration of sildenafil improves endothelial function in spontaneously hypertensive rats by decreasing COX-2 expression and oxidative stress.

AIMS: Spontaneously hypertensive rats (SHR) exhibit impaired endothelial vasodilation and enhanced vasoconstriction. The phosphodiesterase 5 (PDE5) inhibitor sildenafil (Sild) potentiates the nitric oxide (NO)-mediated effects exerting antioxidative and anti-inflammatory actions. In the present study, we hypothesized that Sild could improve endothelial function in SHR. MATERIALS AND METHODS: Male rats were treated daily for 60 days by oral gavage with Sild (45 mg/kg) before the onset of the hypertensive state (pre-hypertensive protocol). The aortic relaxation to acetylcholine (ACh), sodium nitroprusside (SNP) and the phenylephrine (Phe)-induced contraction was evaluated in SHR. Protein expression of eNOS, p-eNOS, caveolin, COX-1, COX-2, ERK and p-ERK was measured by Western blot. KEY FINDINGS: Resting blood pressure was not modified by Sild administration. Treatment with Sild did not alter the relaxation response to SNP but improved the ACh-induced relaxation and reduced Phe-induced contraction in aortic rings from SHR. This protective effect of Sild could be attributed to reduced superoxide anions (O2-) generation, cyclooxygenase type 2 (COX-2) protein downregulation and increased NO bioavailability. SIGNIFICANCE: Sild improves endothelial function in SHR aorta without affecting resting blood pressure values. These results indicate that PDE5 inhibition has a potential role in the improvement of vascular function and could be an adjuvant in the treatment of essential hypertension.

Mechanisms underlying the vasorelaxant effect of trans-4-methoxy-ß-nitrostyrene in the rat mesenteric resistance arteries.

Mechanisms underlying the vasorelaxant effects of the synthetic nitro compound, trans-4-methoxy-ß-nitrostyrene (T4MN) were studied in isolated small resistance arteries from spontaneously hypertensive rats (SHRs). T4MN caused vasorelaxation in endothelium-intact third-order branches of the mesenteric artery pre-contracted with noradrenaline (NA). This effect was unchanged by indomethacin and atropine but was significantly reduced by endothelium removal, L-NAME, LY294002, glybenclamide, TEA, apamin, TRAM 34, or by the association of apamin and TRAM 34. Pretreatment with the sGC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) reduced the T4MN-induced relaxation in endothelium-intact, but not in denuded preparations. Incubation of small resistance arteries with T4MN increased nitric oxide (NO) production, an effect that was blocked by L-NAME. In Ca2+-free medium, T4MN inhibits the contractions induced by (i) NA, (ii) exogenous calcium through receptor- or voltage-operated Ca2+ channels and (iii) those evoked by Ca2+ influx through stores-operated Ca2+ channels activated by thapsigargin-induced Ca2+ store depletion. In contrast, T4MN was inert against the transient contraction induced by caffeine in Ca2+-free medium. In conclusion, T4MN induced effective vasorelaxant effects in isolated small resistance arteries from SHRs. This vasorelaxation seems to be mediated partly by an endothelium-dependent mechanism involving activation of Akt/eNOS/NO pathway and partly by an endothelium-independent mechanism through activation of sGC/cGMP/PKG pathway in vascular smooth muscle, leading to inhibition of Ca2+ influx from the extracellular milieu and IP3-sensitive intracellular Ca2+ release as well as activation of potassium channels.

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.

Vasodilator effects and putative guanylyl cyclase stimulation by 2-nitro-1-phenylethanone and 2-nitro-2-phenyl-propane-1,3-diol on rat aorta.

Compounds containing a nitro group may reveal vasodilator properties. Several nitro compounds have a NO2 group in a short aliphatic chain connected to an aromatic group. In this study, we evaluated in rat aorta the effects of two nitro compounds, with emphasis on a putative recruitment of the soluble guanylate cyclase (sGC) pathway to induce vasodilation. Isolated aortic rings were obtained from male Wistar rats to compare the effects induced by 2-nitro-1-phenylethanone (NPeth) or 2-nitro-2-phenyl-propane-1,3-diol (NPprop). In aortic preparations contracted with phenylephrine or KCl, NPeth and NPprop induced vasorelaxant effects that did not depend on the integrity of vascular endothelium. NPeth had a lesser vasorelaxant efficacy than NPprop and only the NPprop effects were inhibited by pretreatment with the sGC inhibitors, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or methylene blue. In an ODQ-preventable manner, NPprop inhibited the contractile component of the phenylephrine-induced response mediated by intracellular Ca2+ release or by extracellular Ca2+ recruitment through receptor- or voltage-operated Ca2+ channels. In contrast, NPprop was inert against the transient contraction induced by caffeine in Ca2+-free medium. In an ODQ-dependent manner, NPprop inhibited the contraction induced by the protein kinase C activator phorbol 12,13-dibutyrate or by the tyrosine phosphatase inhibitor sodium orthovanadate. In silico docking analysis of a sGC homologous protein revealed preferential site for NPprop. In conclusion, the nitro compounds NPeth and NPprop induced vasorelaxation in rat aortic rings. Aliphatic chain substituents selectively interfered in the ability of these compounds to induce vasorelaxant effects, and only NPprop relaxed aortic rings via a sGC pathway.

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.

Endothelium-independent vasodilator effect of 2-nitro-1-phenyl-1-propanol on mesenteric resistance vessels in rats.

2-Nitro-1-phenyl-1-propanol (NPP) is a nitro alcohol with vasodilator activity in the rat aorta. The present study investigated the vasodilator properties of NPP in small vessels of the mesenteric bed, which, contrary to the aorta, contains resistance vessels. Using myography, isometric contractions were recorded in rings of second- and third-order branches from the rat mesenteric artery. NPP relaxed mesenteric ring preparations that were contracted with phenylephrine, U-46619, and KCl (40mM), resulting in significantly different EC50 values (0.41µM [0.31-0.55µM], 0.16µM [0.10-0.24µM], and 4.50µM [1.86-10.81µM], respectively). NPP-induced vasodilation decreased as the extracellular K+ concentration increased. The pharmacological blockade of K+ channels with tetraethylammonium, BaCl2, CsCl, and apamin also blunted NPP-induced vasorelaxation. In contrast, NPP-induced vasodilation was resistant to indomethacin, L-NG-nitroarginine methyl ester (L-NAME), and endothelium removal, indicating that neither prostaglandins nor the endothelial release of nitric oxide is involved in the relaxant effects of NPP. Conversely, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), cis-N-(2-phenylcyclopentyl)-azacyclotridec-1-en-2-amine hydrochloride (MDL-12,330A), and H-89 reduced NPP-induced vasodilation. Under Ca2+-free conditions, NPP did not alter transient contractions that were evoked by caffeine, but it reduced transient contractions that were evoked by phenylephrine. In mesenteric rings that were loaded with the fluorescent Ca2+ indicator Fluo-4 AM and stimulated with phenylephrine, NPP blunted both contractions and fluorescence signals that were related to cytosolic Ca2+ levels. In conclusion, the vasodilatory actions NPP on mesenteric vessel resistance involved the participation of cyclic nucleotides and the opening of K+ channels.

Cardiovascular Effects of the Essential Oil of Croton argyrophylloides in Normotensive Rats: Role of the Autonomic Nervous System.

Cardiovascular effects of the essential oil of Croton argyrophylloides Muell. Arg. (EOCA) were investigated in normotensive rats. In saline-pretreated anesthetized or conscious rats, intravenous (i.v.) injection of the EOCA induced dose-dependent hypotension. Dose-dependent tachycardia was observed only in conscious rats. In anesthetized rats, cervical bivagotomy failed to enhance EOCA-induced hypotension but unmasked significant bradycardia. In conscious rats, i.v. pretreatment with methylatropine, but not with atenolol or L-NAME, reduced both hypotensive and tachycardiac responses to EOCA. However, hexamethonium pretreatment reverted the EOCA-induced tachycardia into significant bradycardia without affecting the hypotension. In aortic ring preparations precontracted with phenylephrine, EOCA induced a concentration-dependent relaxation that was significantly reduced by vascular endothelium removal and pretreatment with atropine, indomethacin, or glibenclamide but remained unaffected by pretreatment with L-NAME or TEA. It is concluded that i.v. treatment with EOAC decreased blood pressure probably through an active vascular relaxation rather than withdrawal of sympathetic tone. Muscarinic receptor stimulation, liberation of the endothelium-derived prostacyclin, and opening KATP channels are partially involved in the aortic relaxation induced by EOCA and in turn in the mediation of EOCA-induced hypotension. EOCA-induced tachycardia in conscious rats appears to be mediated reflexly through inhibition of vagal drive to the heart.

Vasorelaxant effects of 2-nitro-1-phenyl-1-propanol in rat aorta.

2-Nitro-1-phenyl-1-propanol (NPP) is a nitro alcohol that is known as an intermediate in the synthesis of sympathomimetic agents, such as norephedrine. The present study investigated the vasoactive effects of NPP on rat aorta. In endothelium-intact aortic rings, NPP fully relaxed contractions that were induced by phenylephrine, KCl, and U-46619. The relaxant effects of NPP on phenylephrine-elicited contractions remained unaffected by NG-nitro-l-arginine methyl ester (l-NAME), indomethacin, propranolol, tetraethylammonium, 4-aminopyridine, and glibenclamide. Conversely, pretreatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), cis-N-(2-phenylcyclopentyl)-azacyclotridec-1-en-2-amine hydrochloride (MDL-12,330A), and N-[2-(P-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-89) reduced the ability of NPP to relax contractions that were elicited by phenylephrine. NPP inhibited the vasoconstrictor response that was induced by Ca2+ in aortic rings that were stimulated by pharmacomechanical or electromechanical coupling with phenylephrine and 60 mmol/L KCl, respectively, and after the depletion of intracellular Ca2+ stores. Such effects of NPP were significantly reversed by pretreatment with the guanylyl cyclase inhibitor ODQ and weakly influenced by the adenylyl cyclase inhibitor MDL-12,330A. In Ca2+ -free medium, NPP inhibited transient contractions that were induced by phenylephrine but not caffeine. In homogenates of aortic rings, NPP increased cyclic guanosine 3',5'-monophosphate (cGMP) and cyclic adenosine 3'-5'-monophosphate levels, but this effect was statistically significant only for cGMP. In conclusion, in contrast to the vasoconstrictor amine norephedrine, NPP is a vasodilator in rat aorta, and its relaxant effects are likely attributable to cGMP production.

Biphasic cardiovascular and respiratory effects induced by ß-citronellol.

ß-Citronellol is a monoterpene found in the essential oil of various plants with antihypertensive properties. In fact, ß-citronellol possesses hypotensive actions due to its vasodilator abilities. Here we aimed to show that ß-citronellol recruits airway sensory neural circuitry to evoke cardiorespiratory effects. In anesthetized rats, intravenous injection of ß-citronellol caused biphasic hypotension, bradycardia and apnea. Bilateral vagotomy, perivagal capsaicin treatment or injection into the left ventricle abolished first rapid phase (named P1) but not delayed phase P2 of the ß-citronellol effects. P1 persisted after pretreatment with capsazepine, ondansetron, HC-030031 or suramin. Suramin abolished P2 of apnea. In awake rats, ß-citronellol induced biphasic hypotension and bradycardia being P1 abolished by methylatropine. In vitro, ß-citronellol inhibited spontaneous or electrically-evoked contractions of rat isolated right or left atrium, respectively, and fully relaxed sustained contractions of phenylephrine in mesenteric artery rings. In conclusion, chemosensitive pulmonary vagal afferent fibers appear to mediate the cardiovascular and respiratory effects of ß-citronellol. The transduction mechanism in P1 seems not to involve the activation of transient receptor potential vanilloid subtype 1 (TRPV1), transient receptor potential ankyrin subtype 1 (TRPA1), purinergic (P2X) or 5-HT3 receptors located on airways sensory nerves. P2 of hypotension and bradycardia seems resulting from a cardioinhibitory and vasodilatory effect of ß-citronellol and the apnea from a purinergic signaling.

Cardiovascular effects of a labdenic diterpene isolated from Moldenhawera nutans in conscious, spontaneously hypertensive rats.

CONTEXT: The labdenic diterpene labd-8(17)-en-15-oic acid (labd-8) isolated from a methanolic extract of Moldenhawera nutans Queiroz & Alkin (Leguminosae) has hypotensive and tachycardiac properties in normotensive rats. A part of the hypotensive effect was due to a reduction in the sympathetic nerve drive to vessels, an event admittedly enhanced in spontaneously hypertensive rats (SHRs). OBJECTIVES: We assessed whether the cardiovascular effects induced by labd-8 could be enhanced in SHRs. MATERIALS AND METHODS: For in vivo experiments, arterial and venous catheters were implanted under anesthesia for blood pressure recording and drug administration, respectively. For in vitro experiments, thoracic aorta rings were suspended in organ baths containing warm (37 °C) perfusion medium that was continuously bubbled with carbogen. RESULTS: Intravenous injection of labd-8 (1, 3, 5, and 10 mg/kg) induced similar dose-dependent hypotension and tachycardia in both SHRs and Wistar-Kyoto rats (WKY). In SHRs, only the tachycardia response to labd-8 was significantly reduced by pretreatment with methylatropine or propranolol. However, both cardiovascular effects of labd-8 were reduced by hexamethonium while remained unchanged by l-NAME. In isolated aortic preparations from SHRs, labd-8 (1-1000 µg/mL) relaxed potassium-induced contractions with an IC50 (geometric mean [95% confidence interval]) value (536.5 [441.0-631.9] µg/mL) significantly greater than that (157.6 [99.1-250.5] µg/mL) obtained in preparations from WKY rats. CONCLUSION: In SHRs, the hypotension induced by labd-8 is associated with a reflex tachycardia and seems mediated partly through withdrawal of sympathetic vasomotor tone and partly through an active vasorelaxation. Its magnitude was not enhanced when compared with WKY rats likely because of impaired vasorelaxant effects of labd-8 in preparations from SHRs.