Effects of endothelin-1 chronic stimulation on electrical restitution, beat-to-beat variability of repolarization, and ventricular arrhythmogenesis.

Chronically elevated levels of endothelin-1 (ET-1) have been detected in several cardiovascular diseases. In this study, we investigated the chronic effects of ET-1 on the electrophysiological characteristics expected to influence the genesis and maintenance of ventricular arrhythmia (VA). Rabbits were randomized to ET-1 (ET-1 group) or 0.9% saline (control group) for 2 weeks. The S1-S2 protocol and S1-S1 dynamic pacing were performed to assess the action potential duration restitution (APDR) and to induce APD alternans or VA in 4 sites of Langendorff-perfused rabbit hearts. The beat-to-beat variability of repolarization was quantified as short-term variability and long-term variability. Compared with the control group, chronic ET-1 administration significantly prolonged QT intervals, APD at 90% repolarization (APD90), and effective refractory period (ERP), steepened the maximum slopes of the APDR curve, decreased the ERP/APD90 ratio, and increased the spatial dispersions of APD90, ERP, and maximum slopes (P < 0.05 for all). Moreover, chronic ET-1 administration markedly increased the short-term variability and long-term variability (P < 0.01 for all). APD alternans occurred in both groups, but the threshold of APD alternans was decreased at all sites in the ET-1 group (P < 0.01 for all). We also observed that chronic ET-1 stimulation significantly increased the incidence and duration of the VA episodes. These results suggest that chronic stimulation with ET-1 facilitated VA by steepening the APDR curve and increasing the spatial dispersion of APDR and beat-to-beat variability of repolarization.

Influence of nuclear factor-κB inhibition on endothelin-1 induced lung edema and oxidative stress in rats.

The aim of the present study is to determine the effects of the BAY 11-7082, a nuclear factor-kappaB (NF-κB) inhibitor, on endothelin-1 (ET-1) induced lung edema, the level of reactive oxygen species (ROS) and tumor necrosis factor alpha (TNF-α) in the lungs. Experiments were carried out on adult male Wistar-Kyoto rats. The animals were divided into 4 groups: Group I: saline-treated control; Group II: saline followed by ET-1 (12.5 µg/kg b.w., i.v.); Group III: BAY 11-7082 (10 mg/kg b.w., i.v.) administered one hour before saline; Group IV: BAY 11-7082 (10 mg/kg b.w., i.v.) administered 1 hour before ET-1 (12.5 µg/kg b.w., i.v.). Injection of ET-1 alone showed a significant (P<0.001) increase in thiobarbituric acid reactive substances (TBARS) and hydrogen peroxide (H(2)O(2)) level as well as a decrease (P<0.01) in GSH level and GSH/GSSG ratio (P<0.02). BAY 11-7082 significantly decreased TBARS (P<0.01) and H(2)O(2) (P<0.05) level as well as improved the redox status (P<0.02) in the lungs. BAY 11-7082 also prevented ET-1 induced lung edema (P<0.05). The concentration of TNF-α (P<0.02) and p65 subunit of NF-κB signaling compound (P<0.001) was increased in the presence of ET-1, while BAY 11-7082 decreased both TNF-α level (P<0.05) and p65 subunit concentration (P<0.01). Our results indicate that BAY 11-7082 plays a protective role in ET-1 induced oxidative lung injury. It successfully prevents lung edema as well as ROS and TNF-α overproduction. Our results also highlight the important role of the NF-κB pathway in ET-1 induced lung injury and ROS overproduction.

Acute neuroprotection by the synaptic blocker botulinum neurotoxin E in a rat model of focal cerebral ischaemia.

Evidence indicates that accumulation of excitotoxic mediators, such as glutamate, contributes to neuronal damage after an ischaemic insult. It is not clear, however, whether this accumulation is due to excess synaptic release or to impaired uptake. To test a role for synaptic release, here we investigated the neuroprotective potential of the synaptic blocker botulinum neurotoxin E (BoNT/E), that prevents vesicle fusion via the cleavage of the SNARE (soluble NSF-attachment receptor) protein SNAP-25 (synaptosomal-associated protein of 25 kDa). Focal ischaemia was induced in vivo by infusing the potent vasoconstricting peptide endothelin-1 (ET-1) into the CA1 area of the hippocampus in adult rats; BoNT/E or vehicle were administered into the same site 20 min later. Injection of ET-1 was found to produce a transient and massive increase in glutamate release that was potently antagonized by BoNT/E. To assess whether blocking transmitter release translates into neuroprotection, the extent of the ischaemic damage was determined 24 h and 6 weeks after the insult. We found that BoNT/E administration consistently reduced the loss of CA1 pyramidal neurons at 24 h. The neuroprotective effect of BoNT/E, however, was no longer significant at 6 weeks. These data provide evidence that blockade of synaptic transmitter release delays neuronal cell death following focal brain ischaemia, and underline the importance of assessing long-term neuroprotection in experimental stroke studies.

Effects of dl-praeruptorin A on cultured neonatal rat ventricular cardiomyocytes with hypertrophy induced by endothelin-1.

The present study investigated whether dl-praeruptorin (Pd-Ia) prevents endothelin-1 (ET-1)-induced cardiomyocyte hypertrophy and the potential pathways that underlie such an effect. We assessed cardiomyocyte surface area, protein synthesis, the expression of Bax/Bcl2 and Jun genes, the expression of atrial natriuretic factor (ANF) and Ca2+/calmodulin-dependent kinase II (CaMK-II) activity in cultured neonatal rat ventricular cardiomyocytes with ET-1-induced hypertrophy. It was found that Pd-Ia decreased the surface area and protein synthesis rate in cardiomyocytes exposed to ET-1. Additionally, the expression of Bcl2 and Bax was increased in both the ET-1-exposed and Pd-Ia+ET- 1-treated groups compared with the control group, although this was not significant. In cardiomyocytes incubated with ET-1, the expression of ANF (Nppa) significantly increased relative to the control and Pd-Ia groups. The expression of Jun significantly increased in cardiomyocytes incubated with ET-1, but not in the Pd-Ia group, where Jun levels were similar to those found for the control group. Moreover, it was found that Pd-Ia inhibited the ET-1-induced increase in intracellular Ca(2+) concentration. The results showed that Pd-Ia could conceivably be an effective therapeutic drug for treating the contractile defects associated with cardiac hypertrophy and failure. This activity may be associated with its Ca2+-antagonist effect and modulation of the expression of immediate-early genes that play important roles in the mitogen-activated protein (MAP) kinase pathway.

[Effect and mechanism of salvianolic acid B in attenuating elevated portal pressure in a rat model of portal hypertension induced by endothelin-1].

OBJECTIVE: To investigate the effects of salvianolic acid B (SA-B) on portal hypertension induced by endothelin-1 in rats. METHODS: Twenty-eight Sprague-Dawley rats were randomly divided into four groups: ET-1 group, ET-1+SA-B group, ET-1+ET(A)R blocker (BQ-123) group and ET-1+ET(B)R blocker (BQ-788) group. The rats of ET-1+SA-B group underwent intragastrical administration of salvianolic acid B for five days before ET-1 injection, while in three other groups' drinking water was given. In BQ-123 group or BQ-788 group, an intravenous injection of BQ-123 or BQ-788 via femoral vein was administered 30 minutes prior to ET-1 injection. Then changes of portal pressure, cervical artery pressure and heart rate were monitored continuously. RESULTS: After ET-1 injection, the portal pressure of all rats in the ET-1 group increased significantly, while slightly in groups that pretreated with SA-B, BQ-123 or BQ-788. CONCLUSION: SA-B can attenuate the elevated portal pressure induced by ET-1 with effect similar to ETR blocker.

Neuroprotective effect of memantine in a rabbit model of optic nerve ischemia.

The purpose of this study was to evaluate the neuroprotective effect of memantine, a N-methyl-D-aspartate antagonist, in an experimental optic nerve ischemia. Endothelin-1 (ET-1) in a dosage of 0.1 microg/day was delivered to the perineural region of the anterior optic nerve by osmotically driven minipumps for 8 weeks in 10 rabbits. In 5 rabbits, 1 mg/kg memantine was administered concurrently by intramuscular injection once a daily. Morphologic optic nerve head changes were monitored with a confocal scanning laser ophthalmoscope. Multivariate statistical analysis showed a significant change in topometric parameters (cup area, cup depth and rim volume), indicating an increase in optic nerve head cupping and a decrease of neural rim volume in the ET-1 administered eyes (P < 0.0001). In rabbits where memantine was given concurrently with ET-1, no significant change in topometric parameters was observed after ET-1 administration (P = 0.78). The current results suggest that memantine has a neuroprotective effect in optic nerve ischemia. Memantine may potentially be useful in the management of various ischemic disorders of the optic nerve, including glaucoma.

Neuroprotective effect of memantine in a rabbit model of optic nerve ischemia

The purpose of this study was to evaluate the neuroprotective effect of memantine, a N-methyl-D-aspartate antagonist, in an experimental optic nerve ischemia. Endothelin-1 (ET-1) in a dosage of 0.1 microg/day was delivered to the perineural region of the anterior optic nerve by osmotically driven minipumps for 8 weeks in 10 rabbits. In 5 rabbits, 1 mg/kg memantine was administered concurrently by intramuscular injection once a daily. Morphologic optic nerve head changes were monitored with a confocal scanning laser ophthalmoscope. Multivariate statistical analysis showed a significant change in topometric parameters (cup area, cup depth and rim volume), indicating an increase in optic nerve head cupping and a decrease of neural rim volume in the ET-1 administered eyes (P < 0.0001). In rabbits where memantine was given concurrently with ET-1, no significant change in topometric parameters was observed after ET-1 administration (P = 0.78). The current results suggest that memantine has a neuroprotective effect in optic nerve ischemia. Memantine may potentially be useful in the management of various ischemic disorders of the optic nerve, including glaucoma.

Rodent models of focal cerebral ischemia.

This unit presents models that are both used to study ischemic mechanisms and to test for neuroprotective agents or agents that enhance recovery from stroke. The Tamura model is one of the best characterized focal ischemia models in which the middle cerebral artery is occluded by electrocoagulation. Also described is the intraluminal monofilament model, the spontaneously hypertensive rat (SHR), and the newer endothelin-1 model. The rationale behind the use of animal models, the various types of models and advantage and disadvantages of each model are presented.

A study of an endothelin antagonist from a Chinese anti-snake venom medicinal herb.

Because it is well known that endothelin (ET) plays an important role in the pathogenesis of cardiovascular diseases, antagonists of ET for clinical use are very important. Because ET and some snake toxins have a homologous structure and similar biologic actions the effect of Chinese anti-snake venom herbal medicines on ET bioactivity was investigated both in vivo and in vitro. Hong Bei Si Chou [Cissus assamica (Laws.) Craib] is a herbal medicine used to treat snake bite in Guangxi province. It was found that all the different fractions of EtOH extraction, the EtOAc part of the EtOH extraction, and resverotrol (3,4'5-trihydroxytransstilbene) isolated from the EtOAc part could antagonize ET both in vivo and in vitro. These three fractions transiently relaxed ET-contracted isolated rat aortic ring in a dose-dependent manner. They also antagonized the lethal effects of ET-1 in mice and inhibited blood pressure elevation induced by ET-1. The results have shown that it is possible to find ET antagonists in Chinese anti-snake venom medicinal herbs. In the future, our work should shed new light on the treatment of cardiovascular diseases in which ET is involved.