Attenuation of Isoflurane Preconditioning-Induced Acute Cardioprotection in Hypertensive Hypertrophied Hearts.

OBJECTIVES: To evaluate the efficiency of isoflurane-induced anesthetic preconditioning and the role of mitochondrial manganese superoxide dismutase (MnSOD) in hypertensive hypertrophied hearts. DESIGN: A prospective animal investigation. SETTING: Medical center hospital research laboratory. PARTICIPANTS: Male spontaneously hypertensive rats (SHRs) and normotensive control Wistar-Kyoto (WKY) rats. INTERVENTIONS: All pentobarbital-anesthetized open-chest rats were subjected to a 45-minute left coronary artery occlusion followed by a 120-minute reperfusion. Before ischemia, both SHR and WKY rats were assigned randomly to receive a 30-minute exposure to 0.9% saline or 1.0 minimum alveolar concentration isoflurane. MEASUREMENTS AND MAIN RESULTS: The myocardial infarct size, assessed as a percentage of the area at risk, was significantly greater in the hypertrophied SHRs than in the WKY rats (65.3%±8.7% v 51.8%±7.2%, p<0.05). Isoflurane preconditioning appreciably reduced the infarct size in the WKY hearts (30.9%±10.5%, p<0.05) but not in the SHR hearts. MnSOD protein expression and enzymatic activity were increased drastically in response to isoflurane exposure in the hearts of the WKY rats (p<0.05) but not in the SHRs. CONCLUSIONS: Isoflurane-induced anesthetic preconditioning is attenuated in hypertensive hypertrophied hearts. This impairment may be associated with the loss of MnSOD augmentation during ischemia and reperfusion.

Nontranscriptional activation of PI3K/Akt signaling mediates hypotensive effect following activation of estrogen receptor ß in the rostral ventrolateral medulla of rats.

BACKGROUND: Estrogen acts on the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons are located, to elicit vasodepressor effects via an estrogen receptor (ER)ß-dependent mechanism. We investigated in the present study nontranscriptional mechanism on cardiovascular effects following activation of ERß in the RVLM, and delineated the involvement of phosphatidylinositol 3-kinase (PI3K)/serine/threonine kinase (Akt) signaling pathway in the effects. METHODS: In male Sprague-Dawley rats maintained under propofol anesthesia, changes in arterial pressure, heart rate and sympathetic neurogenic vasomotor tone were examined after microinjection bilaterally into RVLM of 17ß-estradiol (E2ß) or a selective ERα or ERß agonist. Involvement of ER subtypes and PI3K/Akt signaling pathway in the induced cardiovascular effects were studied using pharmacological tools of antagonists or inhibitors, gene manipulation with antisense oligonucleotide (ASON) or adenovirus-mediated gene transfection. RESULTS: Similar to E2ß (1 pmol), microinjection of ERß agonist, diarylpropionitrile (DPN, 1, 2 or 5 pmol), into bilateral RVLM evoked dose-dependent hypotension and reduction in sympathetic neurogenic vasomotor tone. These vasodepressive effects of DPN (2 pmol) were inhibited by ERß antagonist, R,R-tetrahydrochrysene (50 pmol), ASON against ERß mRNA (250 pmol), PI3K inhibitor LY294002 (5 pmol), or Akt inhibitor (250 pmol), but not by ERα inhibitor, methyl-piperidino-pyrazole (1 nmol), or transcription inhibitor, actinomycin D (5 or 10 nmol). Gene transfer by microinjection into bilateral RVLM of adenovirus encoding phosphatase and tensin homologues deleted on chromosome 10 (5 × 10(8) pfu) reversed the vasodepressive effects of DPN. CONCLUSIONS: Our results indicate that vasodepressive effects following activation of ERß in RVLM are mediated by nongenomic activation of PI3K/Akt signaling pathway. This study provides new insight in the intracellular signaling cascades involved in central vasodepressive functions of estrogen.

Activation of estrogen receptor beta-dependent nitric oxide signaling mediates the hypotensive effects of estrogen in the rostral ventrolateral medulla of anesthetized rats.

BACKGROUND: Apart from their well-known peripheral cardiovascular effects, emerging evidence indicates that estrogen acts as a modulator in the brain to regulate cardiovascular functions. The underlying mechanisms of estrogen in central cardiovascular regulation, however, are poorly understood. The present study investigated the cardiovascular effects of 17beta-estradiol (E2beta) in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons are located, and delineated the engagement of nitric oxide (NO) in E2beta-induced cardiovascular responses. METHODS: In male Sprague-Dawley rats maintained under propofol anesthesia, the changes of blood pressure, heart rate and sympathetic vasomotor tone after microinjection bilaterally into the RVLM of a synthetic estrogen, E2beta were examined for at least 120 min. The involvement of ERalpha and/or ERbeta subtypes was determined by microinjection of selective ERalpha or ERbeta agonist into bilateral RVLM. Different NO synthase (NOS) inhibitors were used to evaluate the involvement of differential of NOS isoforms in the cardiovascular effects of E2beta. RESULTS: Bilateral microinjection of E2beta (0.5, 1, or 5 pmol) into the RVLM dose-dependently decreased systemic arterial pressure (SAP) and the power density of the vasomotor components of SAP signals, our experimental index for sympathetic neurogenic vasomotor tone. These cardiovascular depressive effects of E2beta (1 pmol) were abolished by co-injection of ER antagonist ICI 182780 (0.25 or 0.5 pmol), but not a transcription inhibitor actinomycin D (10 nmol). Like E2beta, microinjection bilaterally into the RVLM of a selective ERbeta agonist 2,3-bis(4-hydroxyphenyl) propionitrile (DPN, 1, 2, or 5 pmol) induced significant decreases in these hemodynamic parameters in a dose-dependent manner. In contrast, the selective ERalpha agonist 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole (5 pmol) did not influence the same cardiovascular parameters. Co-administration bilaterally into the RVLM of NOS inhibitor NG-nitro-L-arginine methyl ester (5 nmol) or selective inducible NOS (iNOS) inhibitor S-methylisothiourea (25 pmol), but not selective neuronal NOS inhibitor 7-nitroindazole (0.5 pmol) or endothelial NOS inhibitor N5-(1-Iminoethyl)-L-ornithine (2.5 pmol), significantly attenuated the cardiovascular depressive effects elicited by DPN (2 pmol). CONCLUSION: Our results indicate that E2beta in the RVLM elicited short-term cardiovascular depressive effects via an ERbeta-dependent nontranscriptional mechanism. These vasodepressor effects of E2beta are likely to be mediated by the iNOS-derived NO in the RVLM.

Autonomic nervous system mediates the cardiovascular effects of Rhodiola sacra radix in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: Rhodiola sacra (Crassulaceae) exhibits cardiovascular bioactivities and is used in Tibetan medicine for promoting circulation and preventing hypertension. However, the underlying mechanisms of its cardiovascular effects are poorly understood. AIM OF THE STUDY: The aim of this study was therefore to evaluate the cardiovascular activity of water-soluble fraction (WtF) and n-butanol-soluble fraction (BtF) of Rhodiola sacra radix and to explore its mechanism of action in propofol anesthetized Sprague-Dawley rats. MATERIALS AND METHODS: The changes of blood pressure, heart rate and cardiac contractility after systemic administration of the extracts (10-75 mg/kg) were examined for at least 40 min. Different antagonists were used to evaluate the mechanisms of cardiovascular effects of the extracts. RESULTS: Intravenous injection of the WtF (10, 25, 35, 50 or 75 mg/kg) exhibited dose-dependent hypotension and increases in heart rate and cardiac contractility. In contrast, mild alterations in the same cardiovascular parameters were detected only at high dose (75 mg/kg) BtF. The WtF-induced hypotensive, positive inotropic and chronotropic effects were significantly abolished by pretreatment with hexamethonium (30 mg/kg, i.v.) or reserpine (5 mg/kg, i.v.), whereas the hypotensive, but not the positive inotropic or chronotropic effect was potentiated by captopril (2.5 mg/kg, i.v.). Pretreatment with methylatropine (1 mg/kg, i.v.), on the other hand, reversed the positive inotropic and chronotropic but not the hypotensive effects of WtF. The WtF-induced cardiovascular responses were not affected in rats pretreated with N(G)-nitro-l-arginine methyl ester (20 mg/kg, i.v.). CONCLUSIONS: We conclude that systemic administration of the WtF of Rhodiola sacra radix elicited a potent hypotensive effect that was mediated by the withdrawal of sympathetic vasomotor tone and interaction with the circulatory angiotensin system. The positive inotropic and chronotropic effects of WtF may result from a direct vagal inhibition on the heart.

Effects of high fructose intake on the development of hypertension in the spontaneously hypertensive rats: the role of AT1R/gp91PHOX signaling in the rostral ventrolateral medulla.

Both genetic and dietary factors determine the development of hypertension. Whether dietary factor impacts the development of hereditary hypertension is unknown. Here, we evaluated the effect of daily high-fructose diet (HFD) on the development of hypertension in adolescent spontaneously hypertensive rats (SHR). Six-week-old SHR were randomly divided into two groups to receive HFD or normal diet (ND) for 3 weeks. The temporal profile of systolic blood pressure, alongside the sympathetic vasomotor activity, in the SHR-HFD showed significantly greater increases at 9-12 weeks of age compared with the age-matched SHR-ND group. Immunofluorescence was used to identify the distribution of reactive oxygen species (ROS), oxidants and antioxidants in rostral ventrolateral medulla (RVLM) where sympathetic premotor neurons reside. In RVLM of SHR-HFD, the levels of ROS accumulation and lipid peroxidation were elevated. The changes in protein expression were measured by Western blot. NADPH oxidase subunit gp91phox and angiotensin II type I receptor were up-regulated in RVLM neuron. On the other hand, the expression of extracellular superoxide dismutase was suppressed. Both molecular and hemodynamic changes in the SHR-HFD were rescued by oral pioglitazone treatment from weeks 7 to 9. Furthermore, central infusion with tempol, a ROS scavenger, effectively ameliorated ROS accumulation in RVLM and diminished the heightened pressor response and enhanced sympathetic activity in the SHR-HFD. Together, these results suggest that HFD intake at adolescent SHR may impact the development of hypertension via increasing oxidative stress in RVLM which could be effectively attenuated by pioglitazone treatment.

Autonomic nervous system and nitric oxide in antihypertensive and cardiac inhibitory effects induced by red mold rice in spontaneously hypertensive rats.

The aim of this study was to investigate the antihypertensive activity of the ethanol extract (EE) of red mold rice (RMR) and to explore its mechanism of action. In comparison to EE of nonfermented rice, the EE of RMR contained higher levels of total phenolic, total flavonoids, gamma-aminobutyric acid, and monacolin K. Intravenous bolus administration of the EE (10-50 mg/kg) resulted in biphasic, dose-dependent antihypertensive effects and decreases in heart rate, cardiac contractility, and sympathetic vasomotor tone in spontaneously hypertensive rats. The initial and delayed antihypertensive responses, and the negative inotropic and chronotropic effects of EE treatment (30 mg/kg, i.v.) were significantly reduced by pretreatment with hexamethonium (30 mg/kg, i.v.) and N(G)-nitro-l-arginine methyl ester (20 mg/kg, i.v.). Pretreatment with methylatropine (1 mg/kg, i.v.), however, reversed the initial but not the delayed bradycardiac and negative inotropic effects of EE. We conclude that systemic administration of the EE of RMR elicited both transient and delayed antihypertensive actions that were mediated by the withdrawal of sympathetic tone and the production of nitric oxide (NO). The negative inotropic and chronotropic effects of EE may result from a direct sympathetic inhibition of the heart as well as an activation of the NO-dependent pathway.

Activation of nitric oxide/cGMP/PKG signaling cascade mediates antihypertensive effects of Muntingia calabura in anesthetized spontaneously hypertensive rats.

We previously reported that the leaf extract of Muntingia calabura L. (Tiliaceae) exerts a potent hypotensive effect in the normotensive rats. The antihypertensive activity of this plant extract, however, is currently unknown. In the present study, we investigated the antihypertensive effects of the n-butanol soluble fraction (BSF) from methanol leaf extract of M. calabura in spontaneously hypertensive rats (SHR), and delineated is underlying mechanisms. The intravenous bolus administration of the BSF (10-100 mg/kg) of M. calabura produced biphasic dose-related antihypertensive and bradycardiac effects in SHR. The BSF-induced initial cardiovascular depressive effects lasted for 10 min, and the delayed effects commenced 40 min and lasted for at least 120 min postinjection. These cardiovascular depressive effects of BSF treatments were greater in SHR than in normotensive Wistar-Kyoto (WKY) rats. Both the initial and delayed antihypertensive and bradycardiac effects of BSF (25 mg/kg, i.v.) in SHR, were significantly blocked by pretreatment with a nonselective nitric oxide (NO) synthase (NOS) inhibitor, a soluble guanylyl cyclase (sGC) inhibitor, or a protein kinase G (PKG) inhibitor. Moreover, the initial effects of BSF in SHR were inhibited by pretreatment with a selective endothelial NOS (eNOS) inhibitor; whereas the delayed effects were attenuated by a selective inducible NOS (iNOS) inhibitor. These results indicate that the BSF from the leaf of M. calabura elicited both transient and delayed antihypertensive and bradycardiac actions in SHR, which might be mediated through NO generated respectively by eNOS and iNOS. Furthermore, activation of sGC/cGMP/PKG signaling pathway may participate in the M. calabura-induced biphasic cardiovascular effects.

New dihydrochalcones and anti-platelet aggregation constituents from the leaves of Muntingia calabura.

Two new dihydrochalcones, 2,3-dihydroxy-4,3',4',5'-tetramethoxydihydrochalcone (1) and 4,2',4'-trihydroxy-3'-methoxydihydrochalcone (2), and a new flavanone, (2R,3R)-(-)-3,5-dihydroxy-6,7-dimethoxyflavanone (3), together with nineteen known compounds have been isolated from the leaves of Muntingia calabura. The structures of three new compounds were determined through spectral analyses including extensive 2D-NMR data. Among the isolates, 2,3-dihydroxy-4,3',4',5'-tetramethoxydihydrochalcone, 5,7-dihydroxy-3-methoxyflavone, 5,7-dihydroxy-6-methoxyflavone, 5,4'-dihydroxy-3,7-dimethoxyflavone, (2S)-7,8,3',4',5'-pentamethoxyflavan, (2S)-5'-hydroxy-7,8,3',4'-tetramethoxyflavan, and methyl gallate exhibited significant anti-platelet aggregation activity in vitro.

Activation of nitric oxide signaling pathway mediates hypotensive effect of Muntingia calabura L. (Tiliaceae) leaf extract.

The cardiovascular effect of the crude methanol extract from the leaf of Muntingia calabura L. (Tiliaceae) was investigated in the anesthetized rats. The crude methanol extract was sequentially fractionated to obtain the water-soluble extract (WSE). Intravenous administration of the WSE (10, 25, 50, 75 or 100 mg/kg) produced an initial followed by a delayed decrease in systemic arterial pressure (SAP) in a dose-dependent manner. The M. calabura-induced initial hypotension lasted for 10 min and the delayed depressor effect commenced after 90 min and lasted for at least 180 min post-injection. The same treatment, on the other hand, had no appreciable effect on heart rate (HR) or the blood gas/electrolytes concentrations. Both the initial and delayed hypotensive effects of WSE (50 mg/kg, i.v.) were significantly blocked by pre-treatment with a nonselective nitric oxide (NO) synthase (NOS) inhibitor, N(G)-nitro-L-arginine methyl ester ((L)-NAME, 0.325 mg/kg/min for 5 min) or a soluble guanylate cyclase (sGC) inhibitor, 1H-[1,2,4]oxadiazole[4,3-alpha]quinoxalin-1-one (ODQ, 0.2 mg/kg/min for 5 min). Moreover, whereas the initial depressor effect of WSE was inhibited by pre-treatment with a selective endothelial NOS (eNOS) inhibitor, N5-(1-Iminoethyl)-L-ornithine ((L)-NIO, 1 mg/kg/min for 5 min), the delayed hypotension was attenuated by a selective inducible NOS (iNOS) inhibitor, S-methylisothiourea (SMT, 0.5 mg/kg/min for 5 min). Administration of WSE also produced an elevation in plasma nitrate/nitrite concentration, as well as an increase in the expression of iNOS protein in the heart and thoracic aorta. These results indicate that WSE from the leaf of M. calabura elicited both a transient and delayed hypotensive effect via the production of NO. Furthermore, activation of NO/sGC/cGMP signaling pathway may mediate the M. calabura-induced hypotension.

Differential role of leptin receptors at the hypothalamic paraventricular nucleus in tonic regulation of food intake and cardiovascular functions.

Leptin plays an important role in the central regulation of body weight and arterial pressure via activation of leptin receptors (Ob-Rs) in the hypothalamic area, including the hypothalamic paraventricular nucleus (PVN). The present study was undertaken to investigate whether endogenous leptin in the PVN plays a dual role in the tonic regulation of body weight and arterial pressure. Adult, male normal-weight Sprague-Dawley rats, which were anesthetized and maintained with propofol, were used. A direct bilateral microinjection into the PVN of an antisense oligonucleotide against Ob-R mRNA (ASON1, 50 pmol) significantly increased the daily food intake and body weight gain, effects which lasted for at least 14 days. The same treatment, on the other hand, had no appreciable effect on the basal mean systemic arterial pressure (SAP), heart rate (HR), or power density of the vasomotor components of SAP signals, the experimental index of neurogenic sympathetic vasomotor tone. ASON1 treatment also exerted an insignificant effect on the baroreceptor reflex control of HR. Western blot analysis revealed that a bilateral microinjection into the PVN of ASON1 (50 pmol) significantly decreased the expression of the Ob-R protein in the hypothalamus. The same treatment also attenuated hypertension, tachycardia, and the increase in the power density of the vasomotor components of the SAP signals induced by exogenous bilateral application of leptin (5 or 50 ng) into the PVN. Control application of sense (SON, 50 pmol) or a scrambled antisense Ob-R oligonucleotide (ASON2, 50 pmol) into the bilateral PVN promoted no discernible effect on Ob-R protein expression in the hypothalamus, on daily food intake, or on cardiovascular performance. Our results indicate that whereas the Ob-Rs in the PVN are involved in the tonic regulation of food intake, they might not be actively involved in the tonic regulation of cardiovascular functions.