Sphingosine 1-phosphate induces sinus tachycardia and coronary vasoconstriction in the canine heart.
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OBJECTIVE: Sphingosine 1-phosphate is a naturally occurring biologically active lysophospholipid. Recent studies suggested that sphingosine 1-phosphate is released into the blood flow from activated platelets upon stimulation to exert multiple biological phenomenon. The purpose of this study was to assess the effects of sphingosine 1-phosphate on sinus automaticity, ventricular contraction and coronary blood flow. METHODS: The canine isolated, blood-perfused sinoatrial node and papillary muscle preparations were used. RESULTS: Sphingosine 1-phosphate increased the sinoatrial rate, while it decreased the coronary blood flow, which was followed by a weak negative inotropic effect. These positive chronotropic and coronary vasoconstrictor effects were not attenuated by the beta- and alpha-adrenoceptor antagonists atenolol and prazosin, respectively. Furthermore, sphingosine 1-phosphate did not affect the adenylate cyclase activity of the membrane preparations made from the canine right atrium and right ventricle, indicating the involvement of a novel signaling pathway in sphingosine 1-phosphate-induced cardiac effects. CONCLUSIONS: These results may provide a clue to better understanding the physiological as well as the pathophysiological regulation of sphingosine 1-phosphate in the heart. (+info)
Effect of beta-adrenoceptor blockers on sarcoplasmic reticular function and gene expression in the ischemic-reperfused heart.
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Although beta-adrenoceptor (beta-AR) blockers are used for the treatment of ischemic heart disease, the mechanisms of their beneficial actions have not been fully elucidated. In view of the role of sarcoplasmic reticular (SR) abnormalities in cardiac dysfunction due to ischemia-reperfusion (I/R), we examined the effects of beta-AR blockers on the I/R-induced changes in SR Ca(2+) uptake and release, as well as the protein contents and gene expression of ryanodine receptor, SR Ca(2+)-pump, phospholamban, and calsequestrin. I/R in isolated rat hearts was induced by stopping the perfusion for 30 min and then reperfusing the ischemic hearts for 60 min. Hearts were treated with or without 10 microM atenolol, a beta(1)-specific blocker, or 10 microM propranolol, a nonspecific beta-blocker, 10 min before inducing ischemia as well as during the reperfusion period. I/R depressed cardiac performance, SR Ca(2+) uptake, and Ca(2+) release activities, protein contents, as well as Ca(2+)/calmodulin-dependent protein kinase and cAMP-dependent protein kinase-mediated phosphorylations, significantly. The mRNA levels for SR Ca(2+) pump, ryanodine receptors, phospholamban, and calsequestrin were also reduced by I/R. All these changes due to I/R were partially prevented by beta-AR blocker treatment. The results indicate that the beneficial effects of beta-AR blockers on cardiac performance in the I/R hearts may be related to the prevention of changes in SR Ca(2+) uptake and release activities, protein contents, as well as Ca(2+)/calmodulin-dependent protein kinase and cAMP-dependent protein kinase phosphorylations of SR proteins. On the other hand, the protection of I/R-induced alterations in mRNA levels for SR proteins by beta-AR blockers suggests cardiac SR gene expression as a molecular site of their cardioprotective action. (+info)
Correction of arterial structure and endothelial dysfunction in human essential hypertension by the angiotensin receptor antagonist losartan.
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BACKGROUND: Structural and functional alterations of the vasculature may contribute to complications of hypertension. Because angiotensin II may be pivotal in some of these vascular abnormalities, we tested the hypothesis that the angiotensin type 1 (AT(1)) receptor antagonist losartan, in contrast to the beta-blocker atenolol, would correct resistance artery abnormalities in patients with essential hypertension. METHODS AND RESULTS: Nineteen untreated patients with mild essential hypertension (47+/-2 years, range 30 to 65 years; 57% male) were randomly assigned in double-blind fashion to losartan or atenolol treatment for 1 year. Nine age/sex-matched normotensive subjects were also studied. Both treatments reduced blood pressure to a comparable degree (losartan, from 149+/-4.1/101+/-1.6 to 128+/-3.6/86+/-2.2 mm Hg, P<0.01; atenolol, from 150+/-4.0/99+/-1.2 to 130+/-3.2/84+/-1.4 mm Hg, P<0.01). Resistance arteries (luminal diameter 150 to 350 microm) dissected from gluteal subcutaneous biopsies were studied on a pressurized myograph. After 1 year of treatment, the ratio of the media width to lumen diameter of arteries from losartan-treated patients was significantly reduced (from 8.4+/-0.4% to 6.7+/-0.3%, P<0.01). Arteries from atenolol-treated patients exhibited no significant change (from 8. 3+/-0.3% to 8.8+/-0.5% after treatment). Endothelium-dependent relaxation (acetylcholine-induced) was normalized by losartan (from 82.1+/-4.9% to 94.7+/-1.1%, P<0.01) but not by atenolol (from 80. 4+/-2.7% to 81.7+/-4.6%). Endothelium-independent relaxation (by sodium nitroprusside) was unchanged after treatment. CONCLUSIONS: The AT(1) antagonist losartan corrected the altered structure and endothelial dysfunction of resistance arteries from patients with essential hypertension, whereas the beta-blocker atenolol had no effect. (+info)
beta-blockade prevents sustained metalloproteinase activation and diastolic stiffening induced by angiotensin II combined with evolving cardiac dysfunction.
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Angiotensin II (Ang II)-mediated sympathostimulation may worsen the progression of cardiac failure, although the nature and mechanisms of such interactions are largely unknown. We previously demonstrated that Ang II combined with evolving cardiodepression (48-hour tachycardia pacing, 48hP) induces marked chamber stiffening and increases metalloproteinases (MMPs). Here, we test the hypothesis that both abnormalities stem from sympathostimulatory effects of Ang II. Forty-eight dogs were instrumented to serially assess conscious ventricular mechanics, MMP abundance and activity, and myocardial histopathology. 48hP combined with 5 days of Ang II (15+/-5 ng. kg(-1). min(-1) IV) more than doubled chamber stiffness (end-diastolic pressure >25 mm Hg, P<0.001), whereas stiffness was unchanged by Ang II or 48hP alone. In vitro and in situ zymography revealed increased MMP abundance and activity (principally 92-kDa gelatinase) from Ang II+48hP. Both stiffening and MMP changes were prevented by cotreatment with high-dose atenolol (which nearly fully inhibited isoproterenol-induced inotropy) but not partial beta-blockade. Myocellular damage with fibroblast/neutrophil infiltration from Ang II+48hP was also inhibited by high- but not low-dose atenolol, whereas collagen content was not elevated with either dose. These data support a role of sympathostimulation by Ang II in modulating myocardial MMP abundance and activity and diastolic stiffening in evolving heart failure and suggest a novel mechanism by which beta-blockade may limit chamber remodeling and diastolic dysfunction. (+info)
In vitro and in vivo evaluation of the antihypertensive drug atenolol in cultured human lymphocytes: effects of long-term therapy.
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The genotoxicity of atenolol, a beta-blocker antihypertensive drug, both in vitro and in vivo, was cytogenetically tested for its ability to induce sister chromatid exchange (SCE) and micronuclei (MN) in cultured peripheral lymphocytes. Also, fluorescence in situ hybridization (FISH) with a centromeric probe was performed to determine the origin of the induced MN. The in vivo study was carried out, on the one hand, on four patients under antihypertensive treatment with atenolol and, on the other hand, on four matched control individuals taking an oral dose of atenolol. The in vitro study was performed on the control individuals by adding the drug to the culture medium at a final concentration similar to the levels found in plasma. When a comparison was made, the frequency of SCE did not show significant differences in any case. A statistically significant increase in the frequency of MN was detected in patients but not in control individuals either in vitro or in vivo. FISH analysis revealed statistically significant differences between patients and control individuals without the drug with respect to the frequency of centromeric signals in MN. Taking all these observations together, our data suggest that chronic exposure to atenolol resulted mainly in the induction of chromosome loss, so an aneugenic activity could be predicted. Different sensitivity to the compound was observed among control individuals. Nevertheless, all of them responded to the presence of atenolol in the same way in both assays. Interindividual variability was also reported. The intervariability seen in patients suggested an adaptive response to the chemical after long-term therapy. (+info)
Influence of diabetes and type of hypertension on response to antihypertensive treatment.
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The aim of our investigation was to determine whether the presence of additional risk factors or type of hypertension (diastolic or isolated systolic) influences blood pressure (BP) response to treatment. The International Nifedipine GITS Study: Intervention as a Goal in Hypertension Treatment (INSIGHT) study is a double-blinded outcome comparison of calcium channel blockade with diuretics in high-risk patients aged 55 to 80 years. Dynamic randomization between nifedipine once daily and hydrochlorothiazide/amiloride was performed to ensure that approximately equal numbers of patients in the 2 groups had each of the major cardiovascular risk factors. Patients with isolated systolic hypertension were also separately randomized. Atenolol or enalapril was the mandatory second-line drug. In 5669 patients who completed the 18-week titration, BP fell from 172+/-15/99+/-9 mm Hg (mean+/-SD) while receiving placebo to 139+/-12/82+/-7 mm Hg. Twenty-six percent of patients required 2 drugs, and 4% required 3 drugs. Patients with diabetes were the most resistant to treatment, requiring second and third drugs 40% and 100% more frequently than patients without diabetes and achieving marginally the highest final BP, for any risk group, of 141+/-13/82+/-8 mm Hg. Age, smoking, gender, hypercholesterolemia, left ventricular hypertrophy, and existing atherosclerosis had little (<1 mm Hg) or no influence on BP at the end of titration, but all except smoking slightly reduced the initial response of either systolic or diastolic BP. Patients with isolated systolic hypertension were slightly more responsive than average to treatment. Our findings suggest that in patients at high absolute risk of cardiovascular complications from hypertension, the risk factors themselves do not prevent the recommended BP targets from being achieved. (+info)
Betaxolol, a beta(1)-adrenoceptor antagonist, reduces Na(+) influx into cortical synaptosomes by direct interaction with Na(+) channels: comparison with other beta-adrenoceptor antagonists.
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Betaxolol, a beta(1)-adrenoceptor antagonist used for the treatment of glaucoma, is known to be neuroprotective in paradigms of ischaemia/excitotoxicity. In this study, we examined whether betaxolol and other beta-adrenoceptor antagonists interact directly with neurotoxin binding to sites 1 and 2 of the voltage-sensitive sodium channel (Na(+) channel) in rat cerebrocortical synaptosomes. Betaxolol inhibited specific [(3)H]-batrachotoxinin-A 20-alpha-benzoate ([(3)H]-BTX-B) binding to neurotoxin site 2 in a concentration-dependent manner with an IC(50) value of 9.8 microM. Comparison of all the beta-adrenoceptor antagonists tested revealed a potency order of propranolol>betaxolol approximately levobetaxolol>levobunolol approximately carteolol>/=timolol>atenolol. None of the drugs caused a significant inhibition of [(3)H]-saxitoxin binding to neurotoxin receptor site 1, even at concentrations as high as 250 microM. Saturation experiments showed that betaxolol increased the K(D) of [(3)H]-BTX-B binding but had no effect on the B(max). The association kinetics of [(3)H]-BTX-B were unaffected by betaxolol, but the drug significantly accelerated the dissociation rate of the radioligand. These findings argue for a competitive, indirect, allosteric mode of inhibition of [(3)H]-BTX-B binding by betaxolol. Betaxolol inhibited veratridine-stimulated Na(+) influx in rat cortical synaptosomes with an IC(50) value of 28. 3 microM. Carteolol, levobunolol, timolol and atenolol were significantly less effective than betaxolol at reducing veratridine-evoked Na(+) influx. The ability of betaxolol to interact with neurotoxin site 2 of the Na(+) channel and inhibit Na(+) influx may have a role in its neuroprotective action in paradigms of excitotoxicity/ischaemia and in its therapeutic effect in glaucoma. (+info)
Beta-adrenergic receptor subtypes differentially affect apoptosis in adult rat ventricular myocytes.
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BACKGROUND-Catecholamine-induced apoptosis is mediated by activation of the beta-adrenergic signaling pathway. We tested the hypothesis that beta(1)- and beta(2)-adrenergic receptor (AR) subtypes differentially affect apoptosis in adult rat ventricular myocytes in vitro. METHODS AND RESULTS-Myocytes were first exposed to norepinephrine (NE) alone (10 mcmol/L) or NE+atenolol (AT) (10 mcmol/L) for 12 hours. AT, a beta(1)-selective AR antagonist, abolished the NE-induced increase in nick end-labeling (TUNEL)-positive cells compared with control (NE, 33+/-3% versus control, 3+/-1%, P<0.0001; NE+AT, 4+/-2% versus control, 3+/-1%, P=0. 98). Annexin V staining, DNA laddering, and caspase activity determinations corroborated these results. Subsequent experiments under prazosin treatment established the apoptosis dose-response curves for the increasingly beta(2)-selective AR agonists isoproterenol (ISO) (beta(1) approximately beta(2)) and albuterol (ALB) (beta(2)>beta(1)). ISO and ALB induced significantly less apoptosis than NE (beta(1)>beta(2)) at equimolar concentrations as assessed by TUNEL staining [1 mcmol/L: NE (8+/-2%) approximately ISO (7+/-1%)>ALB (2+/-1%); 10 mcmol/L: NE (35+/-2%)>ISO (23+/-1%)>ALB (3+/-1%); 100 mcmol/L: NE (50+/-2%)>ISO (29+/-2%)>ALB (14+/-1%), P<0.0001 except for NE versus ISO at 1 mcmol/L with P=0.62]. ALB-induced apoptosis at 100 mcmol/L was abolished by AT (10 mcmol/L), indicating a beta(1)AR-mediated effect. Importantly, ICI 118551 (0.1 mcmol/L), a highly selective beta(2)AR antagonist, did not decrease the percentage of NE-, ISO-, and ALB-induced apoptosis. Reverse transcription-polymerase chain reaction studies revealed that AT completely reversed the beta-adrenergic signaling-induced changes in the Bcl-2-to-Bax ratio. CONCLUSIONS-These observations provide evidence that beta AR-mediated apoptotic death signaling is largely dissociated from beta(2)ARs and selectively mediated by beta(1)ARs in adult rat ventricular myocytes. (+info)