Effects of calcium antagonists on endothelin-1-induced myocardial ischaemia and oedema in the rat

Influence of Endothelin 1 Receptor Blockers and a Nitric Oxide Synthase Inhibitor on Reactive Oxygen Species Formation in Rat Lungs

This study was designated to estimate protective role of ETA and ETB receptor antagonist against endothelin 1 (ET-1)-induced oxidative stress in lungs and determine whether these effects are mediated by nitric oxide (NO) synthase. Experiments were performed on Wistar rats divided into the following groups: I – saline (0.9 % NaCl); II – ET-1 (3 μg/kg b.w.), III – BQ123 (1 mg/kg b.w.) + ET-1 (3 μg/kg b.w.), IV – BQ788 (3 mg/kg b.w.) + ET-1 (3 μg/kg b.w.), V – N-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg b.w.) + ET-1 (3 μg/kg b.w.). ETA and ETB receptor antagonists or L-NAME were administered 30 min before ET-1 injection. The levels of the following substances were measured in the lungs homogenates: thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H2O2), reduced glutathione (GSH) and tumor necrosis factor-alpha (TNF-α). The results showed that ET-1 significantly increased TBARS, H2O2 (respectively: p<0.001, p<0.02) and TNF-α levels (p<0.02) and decreased the GSH level (p<0.01) vs. control group. On the other hand, prior administration of ETA receptor blocker (BQ123) significantly attenuated TBARS (p<0.01), H2O2 (p<0.02), TNF-α (p<0.02) and increased GSH (p<0.02) levels vs. ET-1. However, prior administration of ETB receptor blocker BQ788 did not cause significant changes in the: TBARS, H2O2 and TNF-α (p>0.05) levels, but significantly increased the GSH level and GSH/GSSG ratio (p<0.05). Administration of L-NAME significantly attenuated TBARS (p<0.001), H2O2 (p<0.05), TNF-α (p<0.01) and increased GSH (p<0.05) levels vs. ET-1. In conclusion, we demonstrated that ET-1 induced oxidative stress in the lungs is mediated by ETA receptors. ETA receptor blockage inhibited generation of free radicals and TNF-α and ameliorated antioxidant properties. Moreover, generation of reactive oxygen species is mediated by NOS in the lungs.

Hypotensive effect of aqueous extract of Averrhoa carambola L. (Oxalidaceae) in rats: an in vivo and in vitro approach

AIM OF THE STUDY

Averrhoa carambola L. (Oxalidaceae) leaves are used in Brazilian traditional medicine to treat hypertension. This study was conducted to evaluate the hypotensive effect of the aqueous extract of Averrhoa carambola (AEAc) and its underlying mechanisms in the isolated rat aorta.

MATERIALS AND METHODS

The effect of AEAc on the mean arterial pressure (MAP) was determined in vivo in anesthetized rats. In vitro, thoracic aortic rings were isolated and suspended in organ baths, and the effects of AEAc were studied by means of isometric tension recording experiments. In HPLC analysis, the fingerprint chromatogram of AEAc was established.

RESULTS

In normotensive rats, AEAc (12.5-50.0 mg/kg, i.v.) induced dose-dependent hypotension. In vitro, AEAc caused a depression in the E(max) response to phenylephrine without a change in sensibility. Also, in a depolarized Ca(2+)-free medium, AEAc inhibited CaCl(2)-induced contractions and caused a concentration-dependent rightward shift of the response curves, indicating that AEAc inhibited the contractile mechanisms involving extracellular Ca(2+) influx.

CONCLUSIONS

These results demonstrate the hypotensive effects of AEAc, and these effects may, in part, be due to the inhibition of Ca(2+), which supports previous claims of its traditional use.

Effects of Rho-kinase inhibitor on vasopressin-induced chronic myocardial damage in rats

The aim of this study was to develop a new model of vasopressin-induced chronic myocardial damage based on sustained ST-segment depression in electrocardiogram (ECG) with progression of myocardial fibrosis in rats. Furthermore, using this model, we examined the prophylactic potential of fasudil, a Rho-kinase inhibitor, against myocardial damage induced by vasopressin. In 10-week old male Donryu rats, intravenous administration of arginine vasopressin (0.5 iu/kg) induced significant ST-segment depression. Two days and one week after the administration of vasopressin, ST-segment depression was -0.19 +/- 0.02 and -0.14 +/- 0.02 mV, respectively. Fasudil (10 and 30 mg/kg, p.o.) significantly attenuated the ST-segment depression induced by vasopressin. One week after the administration of vasopressin, the percent area of myocardial fibrosis in control animals (0.42 +/- 0.11%, p < 0.01) was significantly greater than that in normal animals (0.05 +/- 0.01%). Fasudil (10 and 30 mg/kg) significantly prevented the development of the fibrosis. We present a new model of chronic myocardial damage based on sustained ST-segment depression with progression of myocardial fibrosis in rats, and suggest that this model may be useful to investigate the treatment of chronic angina. Inhibition of Rho-kinase is efficacious in preventing the ECG change and development of fibrosis induced by vasopressin in this model.

Endothelin A but not endothelin B receptor blockade reduces capillary permeability in severe experimental pancreatitis

INTRODUCTION

Microcirculatory disorders, in particular increased capillary permeability (CapPerm), contribute to the multiple organ dysfunction syndrome in severe acute pancreatitis (AP). Endothelin receptor antagonists (ET-RA) have been shown to stabilize capillary leakage and improve organ function in AP.

AIM

To find out which endothelin receptor subtype (ET-A or ET-B) mediates the changes in CapPerm.

METHODOLOGY

Severe AP was induced in rats by intraductal bile salt infusion and i.v. cerulein. Animals were randomized to receive (1) saline; (2) selective ET-A-RA (LU-135252; 30 mg/kg); (3) selective ET-B-RA (A-192621); (4) nonselective ET-RA (LU-135252; 120 mg/kg); or (5) combined ET-A/B-RA (30 mg/kg LU-135252 + A-192621). Capillary blood flow (CBF) and CapPerm in the pancreas and colon and leukocyte rolling in mesenteric venules were determined.

RESULTS

Selective ET-A-RA increased CBF and decreased CapPerm in the pancreas and colon by 90-147% and reduced leukocyte rolling in AP but had no effect in healthy controls. Selective ET-B-RA increased pancreatic CBF (2.3 +/- 0.03 versus 2.1 +/- 0.04 nL/min) and enhanced CapPerm in the pancreas and colon by 24-35% in healthy controls but had no effect in AP. Blockade of both receptors produced effects similar to but less pronounced than those of selective ET-A-RA.

CONCLUSIONS

Blockade of ET-A and ET-B receptors has different effects on CapPerm in healthy animals and those with AP. This may explain the inconclusive results reported with nonselective ET-RA. In severe AP, blockade of ET-A but not ET-B receptors reduces CapPerm.

Antiischemic properties of fasudil in experimental models of vasospastic angina

We studied the antiischemic properties of fasudil, a Rho-kinase inhibitor, in conscious rabbits with coronary vasospasm induced by vasopressin and endothelin. Pretreatment with fasudil (0.3 and 3 mg/kg) attenuated the maximum elevation of the T-wave elicited by endothelin. Pretreatment with fasudil inhibited the T-wave elevation elicited by vasopressin. Fasudil and hydroxy fasudil, an active metabolite of fasudil, relaxed the endothelin-, U-46619-, 5-hydroxytryptamine- or histamine-induced contraction in swine coronary arterial strips. Fasudil and hydroxy fasudil significantly prevented the reduction in coronary flow by vasopressin in the Langendorff perfused rat heart. Fasudil was effective in protecting the heart against vasopressin and endothelin-induced myocardial ischemic change in conscious rabbits, and this beneficial effect can be attributed to its action of ameliorating the severe contraction of arteries. The inhibition of Rho-kinase may have implications for the development of novel therapeutic strategies for vasospastic angina in patients.

Comparison of the effects of nifedipine and nisoldipine on coronary vasoconstriction in the Langendorff-perfused rat heart

By using Langendorff-perfused rat hearts, we compared the relaxant effects of two dihydropyridine calcium antagonists (nifedipine and nisoldipine) on the coronary vasculature. Hearts were perfused at a constant flow rate (13 ml/min), and the coronary perfusion pressure was monitored to assess vasoconstriction and relaxation. Administration of 5 nM endothelin significantly increased the perfusion pressure within 5 min, and it did not decrease during the subsequent 10-min washout period. Washout with 1 nM nisoldipine or 10 nM nifedipine almost completely normalized the perfusion pressure. Administration of a nitric oxide synthase inhibitor, N(G)-nitro-L-arginine (100 microM), elevated the perfusion pressure at 5 min. When 1 nM nifedipine was added to the perfusate, it failed to decrease the pressure, but 10 and 100 nM nifedipine partly decreased it (96.4+/-8.2 and 87.0+/-8.8 mm Hg for 10 and 100 nM, respectively). Nisoldipine alleviated the pressure elevation almost completely at 10 nM (60.0+/-5.2 mm Hg). The vasodilatory effect of nisoldipine was also approximately 10 times more potent than that of nifedipine when coronary vasoconstriction was induced by hypoxia-reoxygenation. These results suggest that nisoldipine has a stronger effect than nifedipine at the organ level, which does not depend on the cause of coronary vasoconstriction.

Effect of verapamil on responses to endothelin-1 in aortic rings from streptozotocin-induced diabetic rats

In this study, we investigated the constrictor responsiveness to endothelin-1 (ET-1, 10-30 n m) of aortic rings (under 1 g resting tension in Krebs-Bicarbonate solution) from 8-weeks streptozotocin (STZ, 65 mg kg-1, i.p)-induced diabetic rats and vehicle-treated control rats. The maximum ET-1-induced contraction of the aorta in diabetic rats was increased by 150%, but the EC50 of ET-1 remained unchanged. Although in both groups, verapamil reduced the constrictor responses to ET-1 (diabetic group P<0.001, control group P<0.05), there were not any significant differences between PD2 values. These results suggest that verapamil inhibits ET-1-induced Ca2+ entry through the L-type channel and this effect did not change in diabetes mellitus.