Cyclooxygenase inhibition with acetylsalicylic acid unmasks a role for prostacyclin in erythropoietin-induced hypertension in uremic rats

We previously reported that thromboxane (TX)A2 synthesis and receptor blockade prevented recombinant human erythropoietin (rhEPO)-induced hypertension in chronic renal failure rats. The present study was designed to investigate the effect of a cyclooxygenase inhibitor, acetylsalicylic acid (ASA), on blood pressure, renal function, and the concentration of eicosano?ds and endothelin-1 (ET-1) in vascular and renal tissues of rhEPO-treated or rhEPO-untreated uremic rats. Renal failure was induced by a 2-stage 5/6 renal mass ablation. Rats were divided into 4 groups: vehicle, rhEPO (100 U/kg, s.c., 3 times per week), ASA (100 mg x kg(-1) x day(-1), and rhEPO + ASA; all animals were administered drugs for 3 weeks. The TXA2- and prostacyclin (PGI2)-stable metabolites (TXB2 and 6-keto-PGF1alpha, respectively), as well as ET-1, were measured in renal cortex and either the thoracic aorta or mesenteric arterial bed. The uremic rats developed anemia, uremia, and hypertension. They also exhibited a significant increase in vascular and renal TXB2 (p < 0.01) and 6-keto-PGF1alpha (p < 0.01) concentrations. rhEPO therapy corrected the anemia but aggravated hypertension (p < 0.05). TXB2 and ET-1 tissue levels further increased (p < 0.05) whereas 6-keto-PGF1alpha was unchanged in rhEPO-treated rats compared with uremic rats receiving the vehicle. ASA therapy did not prevent the increase in systolic blood pressure nor the progression of renal disease in rhEPO-treated or rhEPO-untreated uremic rats, but suppressed both TXB2 and 6-keto-PGF1alpha tissue concentrations (p < 0.05). ASA had no effect on vascular and renal ET-1 levels. Cyclooxygenase inhibition had no effect on rhEPO-induced hypertension owing, in part, to simultaneous inhibition of both TXA2 and its vasodilatory counterpart PGI2 synthesis, whereas the vascular ET-1 overproduction was maintained. These results stress the importance of preserving PGI2 production when treating rhEPO-induced hypertension under uremic conditions.     

Role of thromboxane in producing portal hypertension following trauma-hemorrhage

Thromboxane A2 (TXA2) and endothelin-1 (ET-1) have been proposed as the important vasoconstrictors that increase portal venous resistance in paracrine or autocrine fashion. We hypothesized that the hepatic damage following trauma-hemorrhage (T-H) is induced by the impaired hepatic circulation due to the increased production of vasoconstrictors such as ET-1 and TXA2 by the liver. To test this, male Sprague-Dawley rats (n = 6/group) were subjected to trauma (i.e., midline laparotomy) and hemorrhage (35-40 mmHg for 90 min followed by fluid resuscitation) or sham operation. At 2 or 5 h after the end of resuscitation, the liver was isolated and perfused and portal inflow pressure, bile flow, and release of ET-1 and thromboxane B2 (TXB2; a stable metabolite of TXA2) into the perfusate were measured. The level of portal pressure was higher at 5 h following T-H compared with 2 h after T-H and sham. The portal pressure was inversely correlated to the amount of bile production. Furthermore, the bile flow was significantly correlated to the hepatic damage as evidenced by release of lactate dehydrogenase into the perfusate. The level of ET-1 at 5 h following T-H in the perfusate after 30 min of recirculation did not show any difference from sham. However, the levels of TXB2 in the T-H group were significantly higher than those in sham at that interval. These results indicate that the increased release of TXA2 but not ET-1 following T-H might be responsible for producing the increased portal resistance, decreased bile production, and hepatic damage.     

Thromboxane A2 from Kupffer cells contributes to the hyperresponsiveness of hepatic portal circulation to endothelin-1 in endotoxemic rats

We examined the role of thromboxane A2 (TXA2) in LPS-induced hyperresponsiveness of hepatic portal circulation to endothelins (ETs) and whether Kupffer cells are the primary source of TXA2 release in response to ET-1 in endotoxemia. After 6 h of LPS (1 mg/kg body wt ip) or saline (control), liver was isolated and perfused with recirculating Krebs-Henseleit bicarbonate buffer at a constant flow rate (100 ml.min(-1).kg body wt(-1)). ET-1 (10 pmol/min) was infused for 10 min. Portal pressure (PP) was continuously monitored during perfusion. Perfusate was sampled for enzyme immunoassay of thromboxane B2 (TXB2; the stable metabolite of TXA2) and lactate dehydrogenase (LDH) assay. ET-1 infusion resulted in a significantly greater increase of PP in the LPS group than in controls. Both TXA2 synthase inhibitor furegrelate (Fureg) and TXA2 receptor antagonist SQ-29548 (SQ) substantially blocked enhanced increase of PP in the LPS group (4.9 +/- 0.4 vs. 3.6 +/- 0.5 vs. 2.6 +/- 0.6 mmHg for LPS alone, LPS + Fureg, and LPS + SQ, respectively; P < 0.05) while having no significant effect on controls. GdCl3 for inhibition of Kupffer cells had similar effects (4.9 +/- 0.4 mmHg vs. 2.9 +/- 0.4 mmHg for LPS alone and GdCl3 + LPS, respectively; P < 0.05). In addition, the attenuated PP after ET-1 was found concomitantly with significantly decreased releases of TXB2 and LDH in LPS rats treated with Fureg, SQ, and GdCl3 (886.6 +/- 73.4 vs. 110.8 +/- 0.8 vs. 114.8 +/- 54.7 vs. 135.2 +/- 45.2 pg/ml, respectively; P < 0.05). After 6 h of LPS, Kupffer cells in isolated cell preparations released a significant amount of TXA2 in response to ET-1. These results clearly indicate that hyperresponsiveness of hepatic portal circulation to ET-1 in endotoxemia is mediated at least in part by TXA2-induced receptor activation, and Kupffer cells are likely the primary source of increased TXA2 release.     

Production of endothelin-1 from the mesenteric arteries of streptozotocin-induced diabetic rats

Release of endothelin-1 (ET-1) from the mesenteric arteries of Wistar rats with streptozotocin-induced diabetes (STZ-DM) rats and nondiabetic rats was measured by a specific enzyme immunoassay following purification using an immunoaffinity column. The mesenteric arteries from STZ-DM rats released a significantly higher amount of ET-1 as compared to control rats (35.8 +/- 2.8 vs 14.9 +/- 2.0 pg/1hr, p less than 0.05). The plasma level of ET-1 in STZ-DM rats was also elevated to a significant extent as compared to controls (5.1 +/- 0.4 vs 3.0 +/- 0.4 pg/ml, p less than 0.05). The systolic blood pressure of STZ-DM rats was significantly higher than of the controls (p less than 0.05). The increased level of plasma ET-1 as well as its release from the mesenteric artery of STZ-DM rats may suggest its release following damage to the endothelium caused by diabetes and/or by associated changes in blood pressure.     

Endothelin-1 induces stimulation of prostaglandin synthesis in cells obtained from canine airways by bronchoalveolar lavage.

Endothelin-1 (ET-1), a potent mediator released by airway epithelial cells, often exerts its effects in the lung through stimulation of arachidonic acid (AA) metabolism. To investigate its range of influence, we studied the action of ET-1 on the synthesis and release of thromboxane (TX)B2, prostaglandin (PG)D2, and histamine from canine airway cells obtained by bronchoalveolar lavage (BAL). ET-1 (10(-10), 10(-9) and 10(-8)M) stimulated production of TXB2 and PGD2 by BAL cell preparations in a dose-related manner in the absence of measurable histamine release. Release of TXB2 was 10-fold higher than that of PGD2. The effect of ET-1 on AA metabolism in alveolar macrophages was evaluated in preparations of purified (greater than 99%) cells labelled for 20-22 hrs with 3H-AA prior to stimulation. ET-1 (10(-8), 10(-7), 10(-6)M) induced significant, dose-related release of 3H-AA and its metabolites from alveolar macrophages, to levels 350% above control. These studies indicate that low levels of ET-1 can stimulate AA metabolism in resident luminal airway cells, including alveolar macrophages, and suggest that the function of these luminal cells may be modulated by the epithelium, in vivo, through the release of this peptide into the airways.     

Effect of nifedipine in cyclosporine-induced nephrotoxicity in rats: roles of the thromboxane and endothelin systems

Cyclosporine (CsA) (45 mg/kg/day for 7 days) administration in female Wistar rats induced significant decrease in creatinine clearance (Ccr) and body weight loss (BWL). Urine volume (V) was not altered and proteinuria (PU) not provoked. These changes were associated with increased urinary endothelin 1 (ET-1) and thromboxane B(2)(TXB(2)) concentrations, and decreased urinary ratios of prostaglandin (6ketoPGF(1 alpha)and PGE(2)) to TXB(2)excretions.Nifedipine (NFD) (0.1 mg/kg/day for 7 days), a calcium channel blocker, administrated in addition to CsA, to another group of animals, significantly augmented Ccr and urine V but did not prevent BWL in comparison to CsA-only treated rats. The urinary ET-1 and TXB(2)concentrations displayed significant and non-significant decrease respectively, while the urinary excretion ratios of 6ketoPGF(1 alpha)/TXB(2)and PGE(2)/TXB(2)were significantly enhanced.These observations indicate that the partial protection of NFD in CsA-induced nephrotoxicity could be attributed to augmented urinary prostanoid ratios of renal vasodilators (6ketoPGF(1 alpha)and PGE(2)) to vasoconstrictor (TXB(2)) excretions, and also to reduced release of rather renal origin ET-1, the most potent mamalian vasoconstrictor peptide known to date. In a previous study, we found that NFD only slightly prevented structural renal damage, induced by CsA. So, the NFD protection refers only to functional toxicity and not to structural damage, mediated at least in part by the preservation of relatively high renal TXB(2)levels. However, other nephrotoxic factors and additional mechanisms could also be implicated in this CsA-induced syndrome.     

Thromboxane blockade reduces blood pressure and progression of renal failure independent of endothelin-1 in uremic rats

This study was designed to investigate the role of eicosanoids, thromboxane A2 (TXA2) and prostacyclin (PGI2) as well as their relationship with endothelin-1 (ET-1) in the pathogenesis of renal parenchymal hypertension. Uremic rats were prepared by renal mass ablation and compared with sham-operated controls. The stable metabolites of TXA2 (TXB2) and PGI2 (6-keto-PGF1alpha) and immunoreactive ET-1 concentrations were measured by specific RIAs in biological fluids and in vascular and renal tissues. To investigate the functional role of TXA2 in the progression of hypertension and renal failure, a group of uremic rats were treated with ridogrel (25 mg/kg/day), a TXA2 synthase inhibitor and receptor antagonist. Renal preproET-1 expression was assessed by Northern blot analysis. Systolic blood pressure (SBP), serum creatinine and proteinuria were found to be higher in uremic rats as compared to sham-operated controls (P < 0.01). TXB2 and ET-1 concentrations were increased in blood vessels, the renal cortex and in urine (P < 0.05). 6-keto-PGF1alpha concentrations were also increased in blood vessels and the renal cortex but decreased in urine (P < 0.05). Ridogrel significantly lowered SBP and proteinuria (P < 0.05) and blunted the increase of serum creatinine. Treatment with ridogrel resulted in a marked fall in vascular, renal and urine TXA2 concentrations, while ET-1 and 6-keto-PGF1alpha concentrations remained unchanged. The preproET-1 expression was higher in uremic rats than in the controls and was unaffected by ridogrel. These results suggest that TXA2 is involved in the pathogenesis of hypertension and renal failure progression in rats with subtotal 5/6 nephrectomy and that this effect is independent of the ET-1 system.     

Bronchopulmonary and pressor effects of big-endothelin-1 in the guinea-pig

Injection of 1 nmol/kg Big-endothelin-1 (ET-1) into anaesthetized and ventilated guinea-pigs did not evoke significant changes in pulmonary inflation pressure and mean arterial blood pressure. In contrast, injection of 1 nmol/kg ET-1 induced marked and rapid bronchoconstrictor and pressor responses. When administered at a dose of 10 nmol/kg, Big-ET-1 induced marked long-lasting changes in pulmonary inflation pressure and mean arterial blood pressure developing slowly as compared to those evoked by ET-1. Furthermore, these increases reached maximal values by 20 min for pulmonary inflation pressure and 45 min for mean arterial blood pressure after injection of the peptide. When Big-ET-1 was incubated with -chymotrypsin [45 min at 37°C, enzyme : substrate ratio (wt/wt) : 0.5%] and injected into guinea-pigs at a dose of 1 nmol/kg, marked bronchoconstrictor and pressor responses were observed, developing with the same kinetics as those evoked by ET-1. The extent of the pressor response was similar and the bronchoconstriction was slightly lower than those evoked upon injection of 1 nmol/kg ET-1 treated or not with -chymotrypsin. The present results indicate that Big-ET exhibits moderate, if any, direct bronchoconstrictor and pressor activities in the guinea-pig. The slow metabolism of Big-ET-1 in an active form probably explains its long-lasting effects at a dose of 10 nmol/kg. This is indirectly confirmed by the in vitro treatment of Big-ET-1 with -chymotrypsin which converts the peptide into an active form.     

Endothelin-1 and endothelin-3 stimulate prostaglandin E2 secretion from the rat median eminence.

The in vitro effects of endothelin-1 (ET-1) and endothelin-3 (ET-3) on the release of prostaglandin (PG)E2 from the rat median eminence were investigated. The addition of ET-1 from 10(-9) M to 10(-6) M stimulated PGE2 release in a dose-dependent manner (from 10.5 +/- 2.1 to 54.4 +/- 5.6 pg/ME fragment/30 min; mean +/- SEM, p less than 0.001). ET-3 also stimulated the release of PGE2 from 10(-7) M to 10(-5) M dose dependently (from 18.1 +/- 0.7 to 60.9 +/- 17.4 pg/ME fragment/30 min p less than 0.05). The time course effect of ET-3 (10(-6) M) showed that PGE2 release was stimulated within five minutes (control, 1.5 +/- 0.5; ET-3, 15.8 +/- 3.0 pg/ME fragment/5 min, p less than 0.01). These results suggest that ET-1 and ET-3 have some physiological effects on the rat median eminence.     

Papaverine effects on PGI2 and TXA2 release from the canine vascular wall.

Operative manipulation of blood vessels might lead to spasm, thereby destroying the endothelial cell function: the spasm can be prevented by the vasodilator papaverine. To study if this was mediated via the prostanoid pathway the following investigation was undertaken: canine jugular veins and carotid arteries were dissected with or without papaverine. Vessel segments were then perfused with Hank's balanced salt solution for five times 15 min. Prostacyclin was measured as the stable degradation product 6-keto-PGF1 alpha and thromboxane as TXB2, by radioimmunoassay. Control arterial segments' 6-keto-PGF1 alpha release was initially 129.5 + 20.1 pg/mm2/15 min, and 29.7 + 10.4 after 60 min (p less than 0.05 vs initial value) and responded to arachidonic acid (AA) with an increase to 139.2 +/- 23.1 pg/mm2/15 min (p less than 0.05). Segments treated with papaverine had the same release as the controls. In venous segments there was a lower initial release (p less than 0.05) from segments given papaverine than from controls, but this was more likely an effect of papaverine on the assay. There was no difference in release of prostacyclin from segments given papaverine in the perfusate compared to controls when using 125I tracer. When using 3H tracer including absorption of free antigen to dextran coated charcoal, papaverine displaced the free tracer giving artificially low values. There was no effect of papaverine given intraoperatively on the TXB2 release, neither from arteries nor from veins. In another experiment the vessel wall tension was examined and the cyclooxygenase inhibitor diclofenac did not inhibit the vasodilating effect of papaverine.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulatory effect of endothelin-1 and -3 on neuronal norepinephrine release in the rat posterior hypothalamus

Based upon the existence of high density of ET-receptors on catecholaminergic neurons of the hypothalamus, we studied the effects of endothelin-1 (ET-1) and endothelin-3 (ET-3) on neuronal norepinephrine (NE) release in the rat posterior hypothalamus. The intracellular pathways and receptors involved were also investigated. Neuronal NE release was enhanced by ET-1 and ET-3 (10 etaM). The selective antagonists of subtype A and B ET receptors (ETA, ETB) (100 etaM BQ-610 and 100 etaM BQ-788, respectively) abolished the increase induced by ET-1 but not by ET-3. The PLC inhibitor, U73122 (10 microM), abolished ET-1 and ET-3 response. GF-109203X (100 etaM) (PKC inhibitor) blocked the increase in NE release produced by ET-3 and partially blocked ET-1 response. The inositol 1,4,5-trisphosphate-induced calcium release inhibitor, 42 microM 2-APB, inhibited the stimulatory effect induced by ET-3 but not by ET-1. The PKA inhibitor, 500 etaM H-89, blocked the increase in neuronal NE release evoked by ET-1 but not by ET-3. Our results showed that ET-1 as well as ET-3 displayed an excitatory neuromodulatory effect on neuronal NE release in the rat posterior hypothalamus. ET-1 through an atypical ETA or ETB receptor activated the PLC/PKC signalling pathway as well as the cAMP pathway, whereas ET-3 through a non-ETA/non-ETB receptor activated the phosphoinositide pathway. Both ETs would enhance the sympathoexcitatory response elicited by the posterior hypothalamus and thus participate in cardiovascular regulation.     

Effects of Hypoxia and Anoxia on the Ex Vivo Release of Prostaglandins from Mouse Cortical Slices

Arachidonic acid is transiently accumulated in the brain as a result of a variety of pathological conditions. The synthesis and release of some of its metabolites, namely, prostaglandin E2 (PGE2), thromboxane B2 (TXB2), and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) from cortical slices of mice were studied following exposure to 6 min of hypoxia (7% O2), 45 s of anoxia, and 5 min-4 h of reoxygenation following anoxia. Hypoxia induced a slight increase in the rate of TXB2 release and a slight decrease in the rate of PGE2 release, whereas 6-keto-PGF1 alpha was unaffected. Anoxia (45 s) followed by reoxygenation induced a transient increase in the release of PGE2 and of 6-keto-PGF1 alpha with a return to the normal rate at 30 min and 2 h of recovery, respectively. However, the rate of TXB2 synthesis and release reached its peak (twofold increase) after 1 h and remained significantly higher than the control rate even after 4 h of normal air breathing. Our results demonstrate that hypoxia and anoxia, even of short duration, selectively trigger the activity of thromboxane synthetase and that this elevated rate of synthesis and release persists long after normal oxygen supply is restored. We suggest that enhanced thromboxane synthesis, with normal prostacyclin levels, might have a role in the pathophysiology of ischemic cell damage.     

复方丹参滴丸对冠心病合并颈动脉粥样斑块患者C-反应蛋白 及血管内皮功能的影响

目的:探讨复方丹参滴丸对冠心病合并颈动脉粥样斑块患者血管内皮功能及C-反应蛋白(C-reactive protein,CRP)水平的影响。方法:选取我院2012年6月-2014年12月期间收治的84例冠心病合并颈动脉粥样斑块患者作为研究对象,并按照随机数字表法将其分为两组,各42例。对照组患者给予阿司匹林肠溶片、他汀类药物等常规药物治疗,而试验组患者在对照组治疗的基础上加服复方丹参滴丸进行治疗,12周为1个疗程。观察并比较两组患者治疗前后的血清CRP水平、肱动脉街道内皮依赖性舒张功能(FMD)、内皮素(ET-1)、一氧化氮(NO)、血栓素B2(TXB2)以及6-酮-前列腺素Fla(6-Keto-PGF-la)的变化情况。结果:治疗12周后,两组患者血清中CRP的水平相对治疗前均显著降低(P0.05),试验组患者降低的程度更为显著(P0.05);对照组患者的FMD、NO和6-Keto-PGF-la指标的水平与治疗前相比较虽有升高的趋势,但均不显著(P0.05),而试验组患者在上述各指标方面的升高程度相对治疗前以及对照组均差异显著(P0.05或P0.01);对照组患者的ET-1和TXB2指标的水平与治疗前相比也有一定的降低趋势,但均不显著(P0.05),而试验组患者在ET-1和TXB2指标方面相对治疗前以及对照组均显著降低(P0.05或P0.01)。结论:复方丹参滴丸可以显著降低冠心病合并颈动脉粥样斑块患者的血清CRP水平,同时对患者的血管内皮功能也具有明显的改善作用。     

Differential response to dexamethasone on the TXB2 release in guinea-pig alveolar macrophages induced by zymosan and cytokines

Glucocorticosteroids reduce the production of inflammatory mediators but this effect may depend on the stimulus. We have compared the time course of the effect of dexamethasone on the thromboxane B2 (TXB2) release induced by cytokine stimulation and zymosan in guinea-pig alveolar macrophages. Interleukin-1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha) and opsonized zymosan (OZ), all stimulate TXB2 release. High concentrations of dexamethasone (1-10 microM) inhibit the TXB2 production induced by both cytokines and OZ, but the time course of this response is different. Four hours of incubation with dexamethasone reduce the basal TXB2 release and that induced by IL-1beta and TNF-alpha, but do not modify the TXB2 release induced by OZ. However, this stimulus was reduced after 24 h incubation. Our results suggest that the antiinflammatory activity of glucocorticosteroids shows some dependence on stimulus and, therefore, may have more than one mechanism involved.     

Plasma thromboxane B2 in haemodialysed patients

Plasma thromboxane B2 (TXB2) concentration was measured in 7 cases of terminal renal failure before and after haemodialysis. The TXB2 levels were higher in the investigated group than in the control group (p less than 0.05). Haemodialysis induced a further increase in the TXB2 concentration. Increased thromboxane production may play a part in the pathogenesis of accelerated atherosclerosis in uraemic patients treated with chronic haemodialysis.     

Comparison of umbilical vein models for measurement of relative prostacyclin and thromboxane production

There is growing evidence that blood vessels generate TXA2 in addition to PGI2. We examined effluents from continuously perfused human umbilical vein and supernatants from umbilical vein rings for TXB2 and 6-keto-PGF1 alpha measurements (stable metabolites of TXA2 and PGI2, respectively). TXB2 and 6-keto-PGF1 alpha were identified in all samples. 6-keto-PGF1 alpha to TXB2 ratio was higher in intact vein effluents than in the venous ring supernatants (112:1 and 28:1, respectively, P less than 0.01). Arachidonate stimulation increased 6-keto-PGF1 alpha and TXB2 levels similarly in the intact vein effluent. In contrast, stimulation of the venous rings resulted in a relatively larger increase in TXB2 than in 6-keto-PGF1 alpha. This caused 6-keto-PGF1 alpha to TXB2 ratio to decline (p less than 0.01). The identity of TXB2 was confirmed in several different ways. These data suggest that 1) human umbilical veins produce TXA2 in addition to PGI2, 2) TXA2 release is more by venous rings than by the intact vein probably reflecting contribution from non-endothelial layers, and 3) arachidonate stimulation causes relatively greater release of TXA2 than of PGI2 from the venous rings, whereas release of PGI2 and TXA2 is similar from the intact vein.     

Interleukin-2 enhances the release of endothelin-1 from the rat mesenteric artery

We measured the ET-1 concentration in plasma and in the perfusate of the mesenteric arteries of rats treated with a therapeutic dose of IL-2 for 7 days (100000 U/Kg, iv.). The plasma ET-1 concentration in rats given IL-2 was 14.2 +/- 3.2 pg/ml which was significantly greater than that in the controls (2.5 +/- 0.4 pg/ml, P less than 0.05). The mesenteric arteries also released a significantly greater amount of ET-1 (29.5 +/- 1.6 pg/h) than that in controls (16.8 +/- 2.3 pg/h, P less than 0.01). The arterial blood pressure was significantly lower after IL-2 treatment than the pre-dosing level (P less than 0.05). It is concluded that IL-2 induces ET-1 release from the vascular wall, possibly as a result of reversible endothelial dysfunction caused by IL-2.     

Endothelin-induced modulation of neuropeptide Y and norepinephrine release from the rat mesenteric bed

The effect of three endothelin (ET) agonists [ET-1, ET-3, and sarafotoxin (STX6C)] on the nerve stimulation-induced release of norepinephrine (NE) and neuropeptide Y-immunoreactive compounds (NPY-ir) from the perfused mesenteric arterial bed of the rat as well as the effect on perfusion pressure were examined. ET-1, ET-3, and STX6C all produced a significant, concentration-dependent decrease in the evoked release of NPY-ir but had no effect on the release of NE. In contrast, all three ETs potentiated the nerve stimulation-induced increase in perfusion pressure. The inhibition of nerve stimulation-induced NPY-ir release by ET-1 was significantly blocked by the ET(A)/ET(B) antagonist PD-142893 and the ET(B) antagonist RES-701-1 but not by the ET(A) antagonist BQ-123. The potentiation of the nerve stimulation-induced increase in perfusion pressure by ET-1 was significantly blocked by PD-142893 and BQ-123 and attenuated by RES-701-1. Prior exposure of the preparation to indomethacin or meclofenamate failed to alter the attenuation of the evoked release of NPY-ir or the potentiation of the increase in perfusion pressure produced by ET-1 or ET-3. These results are consistent with the idea that sympathetic cotransmitters can be preferentially modulated by paracrine mediators at the vascular neuroeffector junction.     

Endothelin-1 in hypertension in the baroreflex-intact SHR: a role independent from vasopressin release

This study sought to identify whether central endothelin (ET) receptor activation contributes to the elevated pressure in spontaneously hypertensive rats (SHR) and whether an ET-stimulated vasopressin (AVP) release mediates the increased pressure. In Wistar Kyoto (WKY) rats, intracerebroventricular ET-1 induced a dose-dependent pressor response that was shifted rightward in SHR. ET(A) antagonism decreased mean arterial pressure in baroreflex-intact SHR (P<0.01), consistent with inhibition of endogenous ET-1, and blocked the pressor response to exogenous ET-1 in both strains. ET-1 increased AVP only after sinoaortic denervation (P<0.05). Contrary to WKY, sinoaortic denervation was required to elicit a significant pressor response with 5 pmol ET-1 in SHR. Sinoaortic denervation permitted ET-1 to increase AVP in both strains, and peripheral V(1) blockade decreased pressure in denervated but not intact rats. After nitroprusside normalized pressure in SHR, the pressor and AVP secretory responses paralleled those in WKY. Thus endogenous ET(A) receptor mechanisms contribute to hypertension, independent of AVP, in baroreflex-intact SHR. Although blunted in the hypertensive state, the arterial baroreflex buffers the ET-1-induced pressor and AVP secretory responses in both strains.     

Endothelin increases [Ca2+]i in rat pancreatic acinar cells by intracellular release but fails to increase amylase secretion.

In individual fura-2 loaded cells of rat pancreatic acini endothelin-1 (ET-1) (10-50 nM) induced sustained oscillations in [Ca2+]i. At higher concentrations a larger, but transient increase in [Ca2+]i was observed, which was largely unaffected by removal of extracellular Ca2+. ET-1 induced the release of Ca2+i from the same store as cholecystokinin (CCK), but with less potency. At concentrations of endothelin which transiently increased Ca2+, ET-1 increased the accumulation of inositol phosphates. Specific binding sites for 125I-endothelin were demonstrated on rat pancreatic acini. A single class of binding sites was identified with an apparent Kd 108 +/- 12 pM and Bmax of 171 +/- 17 fmol/mg for ET-1. The relative potency order for displacing [125I]ET was ET-1 greater than ET-2 greater than ET-3. In contrast to CCK and the non-phorbol ester tumour promoter Thapsigargin (TG) which induce both transient and sustained components of [Ca2+]i elevation, ET-1 failed to increase amylase release over the range 100 pM-1 microM.