Endothelin-secreting tumor

Plasma endothelin-1 levels in patients with complex regional pain syndrome

The clinical characteristics of complex regional pain syndrome (CRPS)--spontaneous and stimulus-evoked pain, autonomic abnormalities, motor dysfunction, and trophic changes in the affected limb--are well known. However, its pathogenesis is unclear, and the diagnosis is often delayed, in part due to lack of objective laboratory tests. Endothelin-1 (ET-1) is a potent vasoconstrictor that has recently been shown to produce pain, allodynia, edema, and muscle weakness, as well as to exert a direct excitatory effect on nociceptive afferents. Furthermore, new evidence indicates that ET-1 is involved in various cancer- and non-cancer-related painful conditions. The aim of the present explorative study was to determine the ET-1 plasma levels in patients with CRPS in an attempt to identify a 'laboratory marker' for CRPS and to search for evidence suggesting that ET-1 may be involved in the pathogenesis of CRPS. ET-1 plasma levels were determined in 20 severely affected CRPS patients, in eight patients with non-CRPS chronic painful conditions, and in 10 healthy volunteers. The results showed that there were no significant differences in ET-1 plasma levels between the three groups. We conclude that the plasma level of ET-1 cannot be regarded as a 'marker' for CRPS. Yet, the possibility that ET-1 is involved in the pathophysiology of CRPS has not been excluded and deserves further investigation.

Basic and therapeutic relevance of endothelin-mediated regulation

Three endothelin family peptides (endothelin-1, -2 and -3) exert an extremely potent and long-lasting vasoconstrictor action as well as other various actions through stimulating two subtypes of receptor (ETA and ETB). Vascular endothelial cells produce only endothelin-1. Although the pharmacological actions of exogenous endothelin-1 have been extensively analyzed, the physiological roles of endogenous endothelin-1 have long been obscure. Using potent and selective receptor antagonists, endothelin-1 has been demonstrated to contribute slightly to the maintenance of regional vascular tone. In gene-targeted mice, endothelin family peptides and their receptors have been shown to play an important role in the embryonic development of neural crest-derived tissues. In addition to its potent vasoconstrictor action, endothelin-1 has direct mitogenic actions on cardiovascular tissues, as well as co-mitogenic actions with a wide variety of growth factors and vasoactive substances. Endothelin-1 also promotes the synthesis and secretion of various substances including extracellular constituents. These effects of endogenous endothelin-1 would appear to be naturally concerned with the development and/or aggravation of chronic cardiovascular diseases, e.g. hypertension, pulmonary hypertension, vascular remodeling (restenosis, atherosclerosis), renal failure, and heart failure. A great many non-peptide and orally active endothelin receptor antagonists have been developed, and shown to exert excellent therapeutic effects in animal models as well as human patients with these diseases.

Effects of endothelin on spontaneous contractions in lymph vessels

A mode of action of endothelin (ET) on spontaneous contractions was investigated in ring preparations of isolated bovine mesenteric lymphatics. ET-1 at concentrations between 10(-10) and 10(-9) M caused a dose-dependent increase in the frequency of spontaneous contractions. The specific ET(A)-receptor antagonist BQ-123 (5 x 10(-7) M) caused a significant inhibition of the ET-1-induced positive chronotropic effect in the ring preparations with and without the endothelium. Mechanical denudation of the lymphatic endothelial cells produced a significant potentiation of the ET-induced positive chronotropic effect. BQ-3020 (10(-8)-10(-7) M), a selective ET(B)-receptor agonist, induced dose dependently negative chronotropic and inotropic effects on the spontaneous contractions in the ring preparations with intact endothelium. Mechanical removal of the endothelium caused a significant reduction of the BQ-3020-induced negative chronotropic and inotropic effects. The ET-1-induced positive chronotropic effect was potentiated by pretreatment with N(omega)-nitro-L-arginine methyl ester (L-NAME) (10(-5) M) but unaffected by aspirin (10(-5) M). Additional treatment with L-arginine (10(-4) M) completely reversed the L-NAME-mediated potentiation of the ET-induced chronotropic effect. These results suggest that stimulation of ET(A) receptors on the lymphatic smooth muscles causes a positive chronotropic effect on the spontaneous contractions, and stimulation of ET(B) receptors on the lymphatic endothelial cells induces a release of nitric oxide, which results in the chronotropic and inotropic effects on spontaneous contractions in isolated bovine mesenteric lymphatics.

Endothelin, vascular hypertrophy, and hypertension

The endothelins (ET-1, 2, and 3) constitute a family of 21 amino-acid peptides with potent biological activities. They are synthesized in several tissues, including the vascular endothelium (ET-1 exclusively) and smooth muscle cells. The production and release of endothelin is stimulated by many factors, hormonal and metabolic, and by growth factors, hypoxia, and shear stress. Released endothelin binds to the endothelin receptors ETA and ETB, the ETA receptors on vascular smooth muscle cells mediating vasoconstriction, and the ETB receptors on the endothelium linked to nitric oxide (NO) and prostacyclin release. The ETA receptors activate the PLC-IP3-DAG transduction pathway, which through an increase in cytosolic Ca2+ and protein kinase C (PKC) causes vasoconstriction and stimulation of vascular smooth muscle cell growth and proliferation. In the pathogenesis of vascular hypertrophy in hypertension, there is a complex interaction between endothelin, angiotensin II, alpha-adrenergic agonists, Ca2+, and other growth factors. In animal models of hypertension, endothelin causes vascular hypertrophy, more pronounced in deoxycorticosterone acetate (DOCA)-salt hypertension in the rat than in the spontaneously hypertensive rate. In humans there is an increase in the plasma concentration of endothelin in severe atherosclerotic disease, but not consistently in hypertension. Evidence for the role of endothelin in the vascular hypertrophy of human hypertension is scanty, but the development of nonpeptide and receptor subtype-selective antagonists will permit meaningful studies, including clinical trials of a new class of antihypertensive agents.

Identification of endothelin-1 in the pathophysiology of metastatic adenocarcinoma of the prostate

Prostate cancer is the second most common cause of death from cancer in U.S. men, and advanced, hormone-refractory disease is characterized by painful osteoblastic bone metastases. Endothelin-1, more commonly known as a potent vasoconstrictor, is a normal ejaculate protein that also stimulates osteoblasts. We show here that plasma immunoreactive endothelin concentrations are significantly elevated in men with metastatic prostate cancer and that every human prostate cancer cell line tested produces endothelin-1 messenger RNA and secretes immunoreactive endothelin. Exogenous endothelin-1 is a prostate cancer mitogen in vitro and increases alkaline phosphatase activity in new bone formation, indicating that ectopic endothelin-1 may be a mediator of the osteoblastic response of bone to metastatic prostate cancer.

Heparin regulates endothelin production through endothelium-derived nitric oxide in human endothelial cells

Heparin shows blood pressure lowering effect in hypertensive patients and animal models. The present study examined the effect of heparin on vasoconstrictor endothelin-1 (ET-1) production in cultured human umbilical vein endothelial cells (ECs) to elucidate the mechanism of antihypertensive effect of heparin. Heparin suppressed both basal and thrombin-stimulated ET-1 mRNA expression paralleled with a decrease in ET-1 peptide release in a dose-dependent manner. Heparin concomitantly enhanced nitric oxide (NO) formation measured by NO2/NO3 levels and cGMP production in ECs. These enhancements were more marked when ECs were stimulated by thrombin. However, these heparin's effects were blunted in the presence of endothelium-derived nitric oxide (EDNO) synthesizing inhibitor NG-monomethyl L-arginine. Therefore, these results suggest that suppression of ET-1 production by heparin is EDNO mediated.

Is endothelin involved in the pathogenesis of hypertension?

Endothelins are a family of potent vasoconstrictor peptides released by endothelial cells. The production of endothelin-1 (ET-1) can be stimulated by aggregating platelets and angiotensin II. It is inhibited by increases in intracellular concentration of cyclic GMP. ET-1 causes biphasic changes in arterial blood pressure and of peripheral resistance in several vascular beds: an initial transient decrease (due to release of nitric oxide, prostacyclin, or both from the endothelium) followed by a sustained increase (mainly due to direct activation of vascular smooth muscle). The vasoconstriction induced by the peptide is inhibited by increases in cyclic GMP. Few studies, except in pregnant women with preeclampsia or eclampsia, indicate that the circulating levels of the peptide are augmented in hypertension. Likewise, the information available on changes in responsiveness to endothelins in blood vessels from hypertensive animals is controversial. Until the effect of selective antagonists on the production or action of the peptide can be determined in hypertensive patients, caution must be exerted when implying a role for endothelin in the pathophysiology of hypertension.