充血性心力衰竭犬肾组织内皮素系统表达的变化

目的：观察充血性心力衰竭犬肾脏内皮素系统表达的变化。方法：快速右心室起搏致心力衰竭犬模型，21只犬随机分为对照组、起搏2周组和起搏4周组。测定血液动力学评价心力衰竭严重程度，放射免疫测定法测定血浆内皮素浓度，RT-PCR法检测肾脏皮质和髓质内皮素系统的表达水平。结果：起搏2周组和起搏4周组血浆内皮素浓度均明显升高，起搏2周组肾髓质内皮素B受体表达水平上升，起搏4周组肾皮质和髓质内皮素前体原、内皮素A受体和内皮素B受体的表达均上升，在肾皮质，以内皮素A受体上升幅度较明显，而在肾髓质，则以内皮素B受体上升为显著。结论：在心力衰竭的不同阶段,肾脏内皮素系统表达的改变参与机体水电解质平衡的调节。     

葡萄糖调节蛋白78在复合致病因素诱导的大鼠肝肺综合征中的作用

目的: 探讨葡萄糖调节蛋白78(GRP78)在大鼠肝肺综合征发病中的作用及其与肠源性内毒素血症的关系。方法: Wistar大鼠被随机分为4周组、6周组和8周组3个时点,采用复合致病因素法制备大鼠肝硬化合并肝肺综合征(HPS)模型,并设标准饮食的正常大鼠作为对照组。采用HE染色观察肺组织病理变化;测定血浆中丙氨酸氨基转移酶(ALT)、内毒素、TNF-α和肺组织匀浆中的TNF-α、丙二醛(MDA)的含量。Western blotting和RT-PCR法检测肺组织标本中GRP78蛋白和mRNA表达水平。结果: 模型组动物血浆内毒素含量随病程进展逐渐增高;肺组织中GRP78蛋白和mRNA的表达随HPS进展逐步增高,且各时点间的表达有显著差异(P<0.05);血浆内毒素与升高的GRP78蛋白水平间呈高度正相关(P<0.01)。血浆ALT和TNF-α含量以及肺组织匀浆中TNF-α和MDA含量随病程进展逐渐增高;血浆内毒素含量以及肺组织中GRP78蛋白分别与血浆TNF-α和肺组织中TNF-α、MDA的含量呈高度正相关(P<0.01)。在各时点,模型组动物血浆TNF-α含量、肺组织匀浆TNF-α、GRP78蛋白及mRNA均显著高于正常对照组(P<0.05)。在第6周和第8周,模型组动物血浆内毒素和ALT的含量以及肺组织匀浆中MDA的含量均显著高于正常对照组(P<0.05)。结论: 肝硬化时形成的肠源性内毒素血症作为内质网应激的重要应激原,通过氧化应激激活肺组织的内质网应激反应导致GRP78表达增高,很可能是HPS发病的重要机制。     

β3受体激动剂BRL-37344促进大鼠心力衰竭及可能的作用机制

目的观察β3肾上腺素能受体激动剂(BRL-37344)对血浆TNF-α、AngⅡ和ET-1水平及心肌重构的影响.方法用异丙肾上腺素(isoproterenol,ISO)诱导心力衰竭大鼠模型.随机分为心衰组(CHF)和BRL组,BRL组给予BRL-37344尾静脉注射,同时另设对照组.结果2和6周时CHF组和BRL组大鼠血浆TNF-α、AngⅡ、ET-1均明显高于对照组(P＜0.01),相同时间点BRL组ET-1水平均高于CHF组(P＜0.01),6周时BRL组AngⅡ也明显高于CHF组(P＜0.01).6周时BRL组上述指标均高于2周时水平(P＜0.01),而CHF组只有TNF-α高于2周时水平(P＜0.05).心衰大鼠心肌细胞破坏和胶原纤维组织增生明显,β3受体蛋白在心衰和应用BRL-37344的大鼠心肌表达很明.显.结论BRL-37344能升高心衰大鼠血浆TNF-α、AngⅡ和ET-1含量,并且能促进左室重构,使心衰恶化.     

低氧性肺动脉高压大鼠肺内5-HT_(1B)受体的分布和表达变化

目的:观察低氧性肺动脉高压(HPH)大鼠体内5-羟色胺(5-HT)水平及其肺内5-羟色胺1B(5-HT1B)受体的分布和表达变化,探讨低氧性肺动脉高压的形成机制。方法:40只健康雄性SD大鼠随机分为正常组(control)、低氧3周组、低氧4周组和低氧5周组。除正常组外,其余3组大鼠分别在低氧环境中饲养3周、4周和5周。测定各组大鼠的平均肺动脉压力(mPAP)、右心室收缩压(RVSP)、右心室肥厚度[RV/(LV+S)%]、血浆和肺组织中5-HT含量。应用免疫组织化学法观察大鼠肺组织中5-HT1B受体的分布和表达,Western blotting法测定大鼠肺组织中5-HT1B受体的蛋白含量。结果:和正常组相比,低氧3周组大鼠的mPAP、RVSP和右心室肥厚度均显著升高(均P0.05),并且随着低氧时间的延长而持续升高(均P0.05)。低氧大鼠血浆和肺组织中5-HT的含量均显著高于正常组大鼠(均P0.05),并随着低氧时间的延长而持续升高(均P0.05)。免疫组织化学结果显示:5-HT1B受体主要分布在正常大鼠肺动脉的内膜层,而平滑肌层中仅有少量表达;和正常组相比,低氧3周组大鼠肺动脉平滑肌层中5-HT1B受体的表达显著增多;随着低氧时间的延长,大鼠肺动脉平滑肌层中5-HT1B受体表达持续增多。Western blotting结果表明,大鼠肺组织中5-HT1B受体的蛋白含量变化和免疫组织化学结果相一致。结论:低氧性肺动脉高压大鼠体内5-HT水平显著升高,其肺动脉中5-HT1B受体呈过度表达,这可能是低氧性肺动脉高压形成的分子机制之一。     

骨髓单个核细胞移植对心肌基质细胞衍生因子1-CXCR4轴的影响

背景：心脏干细胞移植后心肌基质细胞衍生因子1-CXCR4轴表达及其作用越来越受到人们的关注。 目的：观察经心外膜注骨髓单个核细胞对心衰犬心脏基质细胞衍生因子1-CXCR4轴 mRNA表达的影响。 方法：16只杂种犬随机数字表法均分为移植组和对照组,植入永久起搏器。右室快速起搏三四周后建立心衰模型。移植组犬经心外膜多点注射骨髓单个核细胞悬液,对照组注射等量生理盐水。 结果与结论：快速起搏三四周后,各项超声参数及血流动力学参数较起搏前改变明显,差异有显著性意义。定量PCR检测细胞移植组基质细胞衍生因子1 mRNA及CXCR4 mRNA表达水平高于对照组(P < 0.01)。说明经心外膜注射的骨髓单个核细胞可提高心肌基质细胞衍生因子1 mRNA及CXCR4 mRNA表达水平。     

心房钠尿肽对脂多糖所致大鼠急性肺损伤的影响

目的:探讨心房钠尿肽(ANP)对脂多糖(LPS)血症大鼠急性肺损伤的作用和机制。方法: 大鼠静脉给予LPS(2 mg·kg^－1)后立即静脉给予ANP(2 μg·kg^－1),记录动物平均动脉血压(MAP)、检测血浆一氧化氮(NO)和内皮素(ET)浓度、测定肺水含量并做肺组织病理学检查。结果: 给予LPS的大鼠,MAP持续下降,至4 h MAP(8.1±2.6)kPa;血浆NO和ET浓度均显著升高(P<0.01 vs control);4 h肺湿干比(5.15±0.43),显著高于对照组(P<0.05);大鼠肺组织病理学检查呈现肺间质水肿。LPS＋ANP组大鼠MAP在给药初期的短暂下降后逐步回升,至4h MAP(13.4±2.9)kPa(P<0.05 vs LPS);4 h血浆NO水平和ET浓度均显著下降(P<0.05 vs LPS),但仍明显高于对照组(P<0.01 vs control);肺湿干比(4.57±0.35)与对照组没有显著差异;肺组织病理学改变较LPS组明显减轻。结论: ANP对LPS引起的急性肺损伤有治疗作用,能调节LPS引起的动脉血压的持续下降,上述作用可能与ANP拮抗ET的产生、降低NO的分泌有关。     

硫化氢供体对大鼠高肺血流性肺动脉高压中内皮素-1及结缔组织生长因子表达的影响

目的：探讨硫氢化钠（NaHS）对大鼠高肺血流性肺动脉高压中内皮素-1(ET-1)及结缔组织生长因子(CTGF)表达的影响。方法:32只雄性SD大鼠随机分为分流组（n=8）、分流+NaHS组（n=8）、假手术组（n=8）和假手术+NaHS组（n=8）。对分流组和分流+NaHS组大鼠行腹主动脉-下腔静脉穿刺建立高肺血流动物模型。分流11周后，分别测定大鼠肺动脉收缩压（SPAP）、血浆ET-1含量、肺组织硫化氢（H2S）含量、肺组织ET-1mRNA的表达及肺动脉CTGF蛋白的表达。结果:分流11周，大鼠SPAP明显高于假手术组(P<0.05)；分流组大鼠肺组织ET-1mRNA表达、血浆ET-1含量以及肺腺泡肌型动脉CTGF表达明显高于假手术组；肺组织H2S含量明显低于假手术组(P<0.05)；应用NaHS干预11周，分流+NaHS组大鼠H2S含量明显高于、而SPAP明显低于假手术组(P<0.05)；分流+NaHS组大鼠血浆ET-1含量及肺组织ET-1mRNA的表达明显低于分流组(P<0.05)；分流+NaHS组大鼠肺动脉CTGF蛋白表达明显低于分流组(P<0.05)。结论: NaHS可能通过降低血管活性肽ET-1 及CTGF在肺组织的表达参与调节高肺血流性肺动脉高压的形成。     

芥子气中毒后肺组织内皮素-1及内皮素A受体的含量和转录表达的研究

目的:探讨内皮素-1(ET-1)、内皮素A受体(ETAR)在芥子气中毒病理生理过程中的作用和地位。方法:应用免疫组化及RT-PCR技术,观测大鼠芥子气中毒后肺组织ET-1、ETAR的转录表达变化,相互关系及与组织损伤的关系。结果:中毒后肺组织ET-1的含量明显高于对照组,2h达峰值,但在12h后低于对照组;中毒后肺组织ET-1及ETAR的mRNA表达均高于对照组,ET-1mRNA在24h仍高于正常,ETARmRNA在24h低于正常组。结论:ET-1及其受体在芥子气中毒后肺的病理生理过程中可能起着重要作用。     

慢性心力衰竭大鼠内皮素系统表达的变化

目的:研究慢性心衰大鼠在心衰早期(冠脉结扎10d)和心衰晚期(冠脉结扎70d)的左心室内皮素受体A(ET_AR)和内皮素受体B(ET_BR)及内皮素前体(PreproET₁)的mRNA表达水平,了解心衰时心肌内皮素系统的变化及其与病程的关系。方法:用逆转录-聚合酶链反应(RT-PCR)检测冠脉结扎心衰模型大鼠的左心室ET_A和ET_B受体及PreproET₁的mRNA表达,以放射免疫技术检测血浆中内皮素(ET₁)和心钠素(ANP)的浓度。结果:冠脉结扎10d后,血浆ET₁、ANP的水平和左心室ET_AR、ET_BR、PreproET₁的mRNA表达水平均明显高于假手术组;冠脉结扎70d后,血浆ET₁和ANP的水平显著高于冠脉结扎10d组和假手术组,ET_A受体mRNA表达水平和假手术组相比无显著性差异,而ET_B受体及PreproET₁mRNA表达水平仍明显高于假手术组,但显著低于冠脉结扎10d组。结论:在慢性心衰的不同阶段,左心室内皮素系统的改变参与机体心脏功能的调节,循环ET₁水平的上升在早期主要是由于PreproET₁的mRNA表达上调所致,在后期则主要与下调的内皮素受体水平有关。     

心房快速起搏对犬心肌基质细胞衍生因子-1表达的影响

目的： 研究心房快速起搏犬模型心肌基质细胞衍生因子-1（SDF-1）的表达。方法： 选用成年健康杂种犬13条,随机分为2组：快速起搏组7条,假手术组6条。2组均开胸于右心耳缝植AOO型起搏器，快速起搏组以400 beats/min起搏6周，假手术组不起搏。在实验结束时，应用逆转录-多聚酶链反应（RT-PCR）测定左心耳、左心房的SDF-1 mRNA表达水平,同时进行左心房的病理及免疫组化分析。结果：快速起搏组犬的左心耳、左心房的SDF-1 mRNA表达水平明显高于假手术组（P<0.05）,分别增高18.5%和22.4%；病理结果示快速起搏组犬左心房心肌细胞变性；免疫组化测定显示快速起搏组犬的左心房SDF-1表达明显多于假手术组，主要分布在心内膜下的心肌细胞内。结论： 心房快速起搏可引起犬心肌组织SDF-1 mRNA及蛋白表达水平增高。SDF-1可能参与心房损伤时心肌组织的修复过程，并对心肌的重构起一定作用。     

Increased levels of endothelin-1 and differential endothelin type A and B receptor expression in scleroderma-associated fibrotic lung disease.

In addition to their vasoactive action, endothelins are potent peptides in the regulation of both cell proliferation and the turnover of extracellular matrix. Using immunohistochemical, autoradiographic, and molecular analyses, we have studied the localization and expression of endothelin-1 and endothelin A (ETA) and B (ETB) receptors in scleroderma-associated fibrotic lung disease. Increased ET-1 immunoreactivity was found in sclerotic tissue compared with control and was associated with the vasculature, pulmonary interstitium, and bronchial and alveolar epithelium. Microautoradiographic analysis after 125I-labeled ET-1 binding showed a two- to threefold increase in the expression of total ET-1 receptors in scleroderma lung tissue localized to the alveolar epithelium and the pulmonary interstitium which was composed of mainly fibroblastic cells with macrophages and some microvessels. RNAse protection assay revealed significantly reduced ETA receptor and slightly raised ETB message levels in systemic sclerosis lung. Surface expression of functional ET receptors was examined by targeted receptor blocking using mixed and receptor-subtype-selective ligands. A consistent decrease in ETA receptor binding sites was noted primarily within the interstitium and vasculature, in contrast to a slight increase in ETB receptors. Elevated ET-1 and the cell-specific pattern of endothelin receptor expression suggest that the endothelins may represent important mediators that influence the pathology of scleroderma-associated lung disease and other fibrotic conditions.     

Expression of endothelin-1 and its receptors in the lungs of broiler chickens exposed to high-altitude hypoxia

To investigate the influence of exposure to high-altitude (HA) hypoxia on the expressions of endothelin-1 (ET-1), endothelin type A (ETA) and endothelin type B (ETB) receptors in broiler chickens, immunohistochemistry studies were performed in the lungs. Six hundred 1-day-old male broiler chickens were randomly divided into two groups: group A, birds maintained under rich oxygen conditions (oxygen content 21%); and group B, birds exposed to HA hypoxia (oxygen content 13%). Our data showed that exposure to altitude elevated ET-1 and ETA gene expressions at 21 and 28 days of age when compared with the rich oxygen group. Meanwhile, a marked decline in ETB expression was observed at 28 days of age in the course of HA, although there were no significant changes (P>0.05) at 7, 14 and 21 days of age. The increased response was accompanied by adverse effects on weekly body weight gain and ascites mortality. These observations suggested that ET-1, ETA and ETB genes are normally expressed in the lungs of birds. Increased levels of ET-1 and ETA and decreased ETB gene expression in the lungs are probably involved in the lung dysfunction of broiler chickens with developmental ascites.     

Endothelin receptor expression in human lungs of newborns with congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a major cause of refractory respiratory failure in the neonatal period and is characterized by persistent pulmonary hypertension of the newborn (PPHN) and pulmonary hypoplasia. Endothelin-1 (ET-1) dysregulation may play a significant role in the pathophysiology of PPHN and ET-1 acts through binding to type A (ETA) and type B (ETB) receptors. Therefore, ETA and ETB receptor protein expression was studied using immunohistochemistry in 10 lung specimens obtained from newborns with CDH, and 4 normal lung specimens, in order to explore whether dysregulation of ETA and ETB expression contributes to PPHN. ETA and ETB mRNAs were then quantified using real-time RT-PCR in laser-microdissected pulmonary resistive arteries. In the lungs of newborns with CDH, immunohistochemistry of both ETA and ETB receptors demonstrated over-expression in the thickened media of pulmonary arteries. Using laser microdissection and real-time RT-PCR, higher levels of ETA and ETB mRNA were found in CDH pulmonary arteries than in controls: this increase was more pronounced for ETA mRNA. This study provides the first demonstration of ET-1 receptor dysregulation in association with structural alteration of pulmonary arteries in newborns with CDH and PPHN. This dysregulation preferentially affects the ETA receptor. These results suggest that dysregulation of ET-1 receptors may contribute to PPHN associated with CDH.     

Early increase in pulmonary vascular reactivity with overexpression of endothelin-1 and vascular endothelial growth factor in canine experimental heart failure

Heart failure is a cause of pulmonary vasoconstriction and remodelling, leading to pulmonary hypertension (PH) and decreased survival. The pathobiology of PH in heart failure remains incompletely understood. We investigated pulmonary vascular function and signalling molecules in early stage PH secondary to experimental heart failure. Eight beagle dogs with overpacing-induced heart failure underwent haemodynamic assessment and postmortem pulmonary arterial reactivity, morphometry and quantification of genes encoding for factors involved in vascular reactivity and remodelling: endothelin-1 (ET-1), ETA and ETB receptors, vascular endothelial growth factor (VEGF), VEGF receptors 1 and 2 (VEGFR1 and VEGFR2), endothelial nitric oxide synthase, angiopoietin-1, bone morphogenetic protein receptors (BMPR1A and BMPR2), serotonin transporter (5-HTT) and the 5-HT(2B) receptor. Overpacing was associated with a decrease in cardiac output and an increase in pulmonary vascular pressures. However, there were no changes in pulmonary vascular resistance or in arteriolar medial thickness. There were increased expressions of genes encoding for ET-1, ETB, VEGF and VEGFR2, while expression of the other genes analysed remained unchanged. In vitro, pulmonary arteries showed decreased relaxation and increased reactivity, while systemic mammary arteries were unaffected. Early PH in heart failure is characterized by altered vasoreactivity and increased ET-1/ETB and VEGF/VEGFR2 signalling.     

Localization and distribution of endothelin receptor subtypes in pulmonary vasculature of normal and hypoxia-exposed rats

To clarify the roles of two different endothelin (ET) receptors in the pulmonary vasculature, the localization and distribution of endothelin-A (ETA) and ETB receptors were investigated in rat lung under normal and hypoxic conditions by an immunohistochemical method. We also carried out in situ hybridization for ETB receptor. In normal rats, ETA receptor is localized in the media of the pulmonary artery and vein with predominant distribution in such proximal segments as elastic arteries and large muscular arteries. ETB receptor is expressed in the intima and media of pulmonary vessels. The distribution of ETB receptor in the media predominates in the distal segments of the pulmonary artery, whereas its distribution in the intima is greater in the proximal segments. Immunoreactivity for ETA receptor increases in the media of the distal segments of the pulmonary artery after exposure to hypobaric hypoxia. Semiquantitative evaluation showed immunoreactivity for ETA receptor in the pulmonary arteries accompanying the terminal bronchioles, respiratory bronchioles, and alveolar ducts to be increased by 2.5-, 5-, and 20-fold after 14 d exposure to hypoxia, respectively. The messenger RNA and immunoreactivity for ETB receptor increased significantly in the intima of the distal segments of pulmonary artery after 7 and 14 d exposure to hypoxia. These results suggest that the vasoconstrictive effects of ET-1 are exerted mainly through ETA receptor in the proximal segments of the pulmonary artery and vein, whereas its effects in the distal segments are mediated by ETA and ETB receptors in normal rats. ETA receptors that increase in resistance arteries after exposure to hypoxia appear to play an important role in the vascular remodeling associated with hypoxic pulmonary hypertension. Because ETB receptors in the endothelium mediate ET-1-induced vasodilatory effects, the increase in endothelial ETB receptors may counteract the development of hypoxic pulmonary hypertension.     

Progestins oppose the effects of estradiol on the endothelin-1 receptor type B in coronary arteries from ovariectomized hyperlipidemic rabbits

OBJECTIVE: Progestins may be associated with the adverse cardiovascular outcomes observed with estrogen plus progestogen therapy, but the mechanism is not resolved. In this study we examined the effect of 17beta-estradiol (E2) alone and in combination with two progestins on the endothelin-1 (ET-1) system in coronary arteries. DESIGN: Watanabe heritable hyperlipidemic rabbits were treated orally with either E2 (4 mg/d), medroxyprogesterone acetate (MPA) (10 mg/d), norethisterone acetate (NETA) (2 mg/d), E2 + MPA, E2 + NETA, or placebo for 16 weeks (n=10 in each group). Coronary arteries were used for mRNA and myograph analyses. RESULTS: E2 alone but not in combination with MPA or NETA increased ETB mRNA expression in coronary arteries. Accordingly, E2 alone but not in combination with MPA or NETA reduced the maximal contraction to ET-1, and the reduction was sustained after ETA but not after ETB blockade. E2 reduced preproendothelin-1 mRNA expression; however, this effect was not blunted by MPA or NETA. ETA and ET-converting enzyme-1 mRNA expression was unaffected by treatment. CONCLUSIONS: The data suggest that long-term E2 treatment selectively attenuates ET-1-induced vasoconstriction, possibly by increasing ETB gene expression in rabbit coronary arteries and that this effect is abolished by the two progestins investigated. This observation may help to explain how progestins oppose the supposed beneficial effects of estrogen on the arterial wall.     

内皮素-1对COPD炎症和氧化应激反应的影响

目的:研究内皮素-1对慢性阻塞性肺疾病(COPD)炎症和氧化应激反应的影响。方法:收集健康不吸烟者(30例)、健康吸烟者(30例)和COPD患者(29例)并诱导其产生痰液,检测内皮素-1在诱导痰中的浓度。采用香烟烟雾提取物刺激SD大鼠,构建肺气肿模型,采用内皮素A受体拮抗剂BQ123和非选择性内皮素受体拮抗剂波生坦进行干预,实验分为对照组、香烟烟雾干预组、选择性内皮素受体拮抗组和非选择性内皮素受体拮抗组。采用Western blot法测定肺组织中cleaved caspase-3的蛋白水平;明胶酶谱法检测肺组织中基质金属蛋白酶2(MMP-2)和基质金属蛋白酶9(MMP-9)的活性;ELISA法检测肺组织上清液中肿瘤坏死因子α(TNF-α)和白细胞介素1β(IL-1β)的浓度;采用生物抗氧化能力(BAP)检测试剂盒检测血清中BAP。结果:内皮素-1在健康吸烟者和COPD患者诱导痰中的浓度显著高于健康不吸烟者(P0.05);COPD患者诱导痰中内皮素-1的浓度高于健康吸烟者(P0.05)。香烟烟雾干预组肺组织中cleaved caspase-3蛋白水平、MMP-2和MMP-9的活性及上清液中TNF-α和IL-1β的含量显著高于对照组(P0.05);内皮素A受体拮抗剂能显著抑制肺组织中cleaved caspase-3蛋白水平、MMP-2和MMP-9的活性及上清液中TNF-α和IL-1β的含量(P0.05)。香烟烟雾干预组血清中的BAP较对照组显著降低(P0.05);内皮素A受体拮抗剂能显著增加血清中的BAP(P0.05)。结论:内皮素-1可能通过调节细胞凋亡、基质金属蛋白酶活性、炎症以及氧化应激反应在COPD发生发展中发挥重要作用。     

Tyrosinase induction and inactivation in normal cultured human melanocytes by endothelin-1

Since endothelin was found to be expressed in epithelial cells as well as in vascular endothelial cells, the functional regulation of melanocytes with endothelin has been actively investigated. In particular, it has been suggested that endothelin may influence pigmentation and depigmentation, which are mediated by melanocytes. In the present study, we investigated the regulation of melanocyte function and tyrosinase expression by endothelin from the point of view of tyrosinase protein expression and enzyme activity. The influence of endothelins on melanocyte function was assessed. Melanocytes showed a dose-dependent increase in cell proliferation with the addition of endothelin-1. When the confluence of melanocytes was cultured with endothelin-1 for 72 h, tyrosinase activity in melanocytes was significantly and dose-dependently decreased. In contrast, there was no significant change with endothelin-3. However, tyrosinase protein expression of melanocytes was significantly and dose-dependently increased by endothelin-1, but endothelin-3 had no effect. Both the suppression of enzyme activity and the enhanced protein expression were regulated by the ETA receptor antagonist, BQ123. In view of these observations, we conclude that endothelin-1-induced tyrosinase is mediated by ETA receptors. However, the reason for the decrease in the specific activity of tyrosinase remains unknown, and our results suggest that another mechanism underlying the activation of tyrosinase is present in addition to the inductive action of endothelin-1 on tyrosinase.