Endothelin cells

Nontraditional Hormones. Novel hormones identified ia cardiovascular tissue have profound effects on maintenance of blood pressure and blood volume ia mammals. Atrial natriuretic hormone (ANH) is a polypeptide hormone secreted from the atria of the heart. When the cardiac atrium is stretched by increased blood volume, secretion of ANH is stimulated ANH ia turn increases salt and water excretion and reduces blood pressure (6). Endothelin is a polypeptide hormone secreted by endothehal cells throughout the vasculature. Although endothelin is released into the circulation, it acts locally in a paracrine fashion to constrict adjacent vascular smooth muscle and increase blood pressure (7). 

Chymase (mast cell protease type II), a chymotrypsin-like protease, is a serine protease found in mucosal mast cells, which catalyzes the conversion of angiotensin I to angiotensin II and of big endothelin 1 (ET1) to ET1 (1-31). 

In 1985, a peptide was described in the supernatants of endothelial cells that mediated vasoconstriction [1]. This peptide was isolated and sequenced, and the cDNA was cloned. According to its origin from endothelial cells it was named endothelin. 

The ECE isoforms show different subcellular distributions and enzymatic characteristics (Table 2). ECE-la and ECE-lc are mainly expressed at the cell surface, whereas ECE-lb, ECE-Id and ECE-2 are expressed intracellularly. Plasma membrane-bound ECE cleaves big-ET-1 circulating in the blood, whereas intracellular ECE isoforms are involved in the generation of mature endothelins. In addition, ECEs (as well as NEP and the insulin-degrading enzyme) contribute to the degradation of amyloid (3 (A 3) peptide. 

ET-1 also stimulates anti-apoptotic signal cascades in fibroblasts, vascular smooth muscles and endothelial cells (via phosphatidylinositol-3-kinase and Akt/pro-tein kinase B). In prostate and ovarian cancer, upregulation of endothelin synthesis and ETA receptors has been associated with a progression of the disease. The inhibiton of ETA receptors results in a reduced tumour growth. In malignant melanoma, ETB receptors are associated with tumour progression. Endothelins can also stimulate apoptosis in stretch-activated vessels via the ETB receptor, which contrasts the above-mentioned effects. The molecular basis for these differential anti- and pro-apoptotic reactions mediated by endothelins remains elusive. 

Sites of endothelin-receptor expression. ETA receptors are expressed in the smooth muscle cells of the vascular medial layer and the airways, in cardiac myocytes, lung parenchyma, bronchiolar epithelial cells and prostate epithelial cells. ETB receptors are expressed in endothelial cells, in bronchiolar smooth muscle cells, vascular smooth muscle cells of certain vessels (e.g. saphenous vein, internal mammary artety), in the renal proximal and distal tubule, the renal collecting duct and in the cells of the atrioventricular conducting system. 

In the interstitium, angiotensin II induces proliferation of mesangial cells and fibroblasts and the synthesis of collagen and other matrix molecules by these cells via the ATI receptor. Moreover, by the concomitant stimulation of chemoattractant cytokines, inflammation is induced. These processes are mediated by endothelin, transforming growth factor(3, and reactive oxygen species, and finally lead to interstitial fibrosis and glomerulosclerosis observed in hypertension and diabetes. 

Most GPCRs interact with and activate more than one G-protein subfamily, e.g., with Gs plus Gq/n (histamine H2, parathyroid hormone and calcitonin recqrtors), Gs plus G (luteinising hormone receptor, 32-adrenoceptor) or Gq/11 plus G12/13 (thromboxane A2, angiotensin ATb endothelin ETA receptors). Some receptors show even broader G-protein coupling, e.g., to Gi, Gq/n plus Gi n ( protease-activated receptors, lysophosphatidate and sphingosine-1-phosphate receptors) or even to all four G-protein subfamilies (thyrotropin receptor). This multiple coupling results in multiple signaling via different pathways and in a concerted reaction of the cell to the stimulus. 

EBV Epstein-Barr virus EC Endothelial cell ECD Electron capture detector ECE Endothelin-converting enzyme E-CEF Eosinophil cytotoxicity enhancing fector... 

Endothelin-1, one of the most potent physiologic vasoconstrictors, is an important contributor to HF pathophysiology.9 Endothelin-1 binds to two G-protein coupled receptors, endothelin-A (ET-A) and endothelin-B (ET-B). Endothelin-A receptors mediate vasoconstriction and are prevalent in vascular smooth muscle and cardiac cells. Endothelin-B receptors are expressed on the endothelium and in vascular smooth muscle, and receptor stimulation mediates vasodilation. Levels of ET-1 correlate with HF functional class and mortality. 

Interleukin-6 (IL-6) is a small polypeptide with a molecular mass of 26 kDa (see Table 2). IL-6 can be induced in various cell types, including fibroblasts, macrophages/monocytes, epithelial cells, T cells, B cells, and diverse tumor cells (L4). TNF, IL-1, and LPS can stimulate IL-6 gene expression in macrophages/monocytes and fibroblasts. In vivo studies showed that systemic administration of TNF, LPS, and IL-1 was followed by a rapid induction of circulating IL-6 (B49, J2). Also, endothelin (ET) at concentrations observed pathophysiolog-ically may trigger production of IL-6 (Ml7). 

In conclusion, the use of specific endothelin antagonists must be considered in the treatment of sickle cell disease as an alternative to HU, whose potential longterm mutagenic/carcinogenic effect is still under debate [36], especially in children. 

Rybicki AC, Benjamin LJ. Increased levels of endothelin-1 in plasma of sickle cell anemia patients [letter]. Blood 1998 92 2594-2596. 

Hammerman SI, Kourembanas S, Con-ca TJ, Tucci M, Brauer M, Farber H.W. Endothelin-1 production during the acute chest syndrome in sickle cell disease. Am J Respir Crit Care Med 1997 156 280-285. 

Pericytes lie periendothelially on the abluminal side of the microvessels (Figure 15.3). A layer of basement membrane separates the pericytes from the endothelial cells and the astrocyte foot processes. Pericytes send out cell processes which penetrate the basement membrane and cover around 20-30% of the micro-vascular circumference [18]. Pericyte cytoplasmic projections encircling the endothelial cells provide both a vasodynamic capacity and structural support to the microvasculature. They bear receptors for vasoactive mediators such as catecholamines, endothelin-1, VIP, vasopressin and angiotensin II. Pericytes become mark-... 

Black PN, Ghatei MA, Takahashi K, Bretherton-Watt D, Krausz T, Dollery CT, Bloom SR (1989) Formation of endothelin by cultured airway epithelial cells. FEBS Lett 255(1) 129-132. 

Since the early 1980s, much effort has focused on animal models of acute and chronic neurodegeneration in search of therapeutics for stroke. Neuronal cell death follows strokes, acute ischemic insults, and chronic neurodegeneration, such as Parkinson s disease, Alzheimer s disease (AD), epilepsy, and Huntington s disease. Up to 80% of all strokes result from focal infarcts and ischemia in the middle cerebral artery (MCA), so the commonly used animal models for neuroprotection are produced by temporary or permanent occlusion of the MCA.5 Lesions of the MCA include occlusion by electrocoagulation, intraluminal monofilaments, photochemical effects, thrombosis, and endothelin-1, but all of these models necessitate studying reperfusion events and validating MCA occlusion by behavioral assessments. 

Endothelin 1 (ETl) is a 21-amino acid peptide released from bronchial cells. It has potent vasoconstrictive agonist properties mediated by two receptor types (A and B). The involvement of the endothelin 1 type A (EDNRA) gene (Afill SNP) in atopy, however, is marginal at best and as yet not widely replicated (181). For... 

Figure 22.4 Injury to endothelial cells can lead to vasospasm. Normal endothelial cells release nitric oxide (NO) which relaxes smooth muscle this is achieved by nitric oxide increasing the concentration of cyclic GMP within smooth muscle fibres and cyclic GMP relaxing the smooth muscle. Injured endothelial cells secrete very little nitric oxide but secrete more endothelin. The latter increases the formation of inositol trisphosphate (IP3), which binds to the sarcoplasmic reticulum (SR) where it stimulates the Ca ion channel. The Ca ion channel in the plasma membrane is also activated. Both effects result in an increase in cytosolic Ca ion concentration, which then stimulates contraction (vasospasm). This reduces the diameter of the lumen of the artery.

Normal endothelial cells produce nitric oxide, which relaxes smooth muscle, whereas damaged cells release less nitric oxide but more of a local hormone, endothelin, which stimulates contraction of smooth muscle (Figure 22.4). 

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