Endothelins stimulate aldosterone secretion from dispersed rat adrenal zona glomerulosa cells, acting through ETB receptors coupled with the phospholipase C-dependent signaling pathway

Aldosterone contributes to hypertension in male mice inducibly overexpressing human endothelin-1 in endothelium

OBJECTIVE

Mechanisms of blood pressure (BP) regulation by endothelin (ET)-1 produced by endothelial cells are complex and remain unclear. Long-term exposure to human ET-1 (hET-1) in mice inducibly overexpressing hET-1 in the endothelium (ieET-1) caused sustained BP elevation. ET-1 has been shown to stimulate the release of aldosterone. Whether aldosterone plays a role in hET-1 overexpression-induced BP elevation and vessel injury is unknown.

METHOD

Nine- to 12-week-old male ieET-1 mice and control mice expressing a tamoxifen-inducible Cre recombinase (CreERT2) in the endothelial cells (ieCre) were treated with tamoxifen for 5 days and studied 3 months later.

RESULTS

Endothelial hET-1 overexpression increased plasma aldosterone levels, which was reversed by 2-week treatment with atrasentan, an endothelin type A receptors blocker. Aldosterone synthase and cryptochrome 2 adrenal cortex mRNA expression was decreased in ieET-1 mice. Two-week treatment with eplerenone, a mineralocorticoid receptor antagonist, reduced systolic BP by 10 mmHg in ieET-1 mice during rest time. Saline challenge-induced sodium excretion and renal cortex thiazide-sensitive sodium-chloride cotransporter mRNA expression were decreased in ieET-1 mice. The sensitivity of mesenteric arteries to contraction by norepinephrine was increased in ieET-1 mice, and was abrogated by eplerenone treatment, whereas sensitivity of endothelium-independent relaxation responses to sodium nitroprusside was enhanced. Resistance artery remodeling was reduced in eplerenone-treated ieET-1 vs. ieET-1 and ieCre mice.

CONCLUSION

These results demonstrate that aldosterone contributes to BP elevation and vascular norepinephrine sensitivity and remodeling caused by hET-1 overexpression in endothelium in mice.

Measurement of plasma endothelin-1 concentration in healthy horses and horses with cardiac disease during rest and after exercise

Cardiac biomarkers are important tools for monitoring disease progress and can monitor progression of therapy. Endothelin-1 (ET-1) has been studied for its use as a cardiac biomarker in human and small animal medicine while in horses with cardiac disease it has not been evaluated yet. The objective of the present study was to determine the concentration of plasma ET-1 in healthy horses and compare it with ET-1 concentration in horses with cardiac disease during rest and after exercise. Fifty four horses admitted to the Equine Clinic of Free University of Berlin were used in the present study, of which 15 horses were clinically healthy with no evidence of cardiac disease (Group 1), 22 horses suffered from cardiac disease with normal heart dimensions (Group 2) and 17 horses with cardiac disease and enlarged heart diameters (Group 3). Clinical examination, electrocardiography and echocardiography were performed. Endothelin-1 concentration was determined using ET-1 ELISA kit. The concentration of plasma ET-1 was significantly increased in horses with cardiac disease and normal cardiac dimensions (Group 2) and in horses with cardiac disease and enlargement of the left atrium (Group 3) compared to its concentration in clinically healthy horses (Group 1). In addition, the concentration of plasma ET-1 after exercise was significantly increased in diseased horses compared to its concentration at rest. Detection of ET-1 plasma concentration in horses at rest may be useful for detecting horses with changes in left atrial cardiac dimensions.

Role of phospholipases in adrenal steroidogenesis

Phospholipases are lipid-metabolizing enzymes that hydrolyze phospholipids. In some cases, their activity results in remodeling of lipids and/or allows the synthesis of other lipids. In other cases, however, and of interest to the topic of adrenal steroidogenesis, phospholipases produce second messengers that modify the function of a cell. In this review, the enzymatic reactions, products, and effectors of three phospholipases, phospholipase C, phospholipase D, and phospholipase A2, are discussed. Although much data have been obtained concerning the role of phospholipases C and D in regulating adrenal steroid hormone production, there are still many gaps in our knowledge. Furthermore, little is known about the involvement of phospholipase A2, perhaps, in part, because this enzyme comprises a large family of related enzymes that are differentially regulated and with different functions. This review presents the evidence supporting the role of each of these phospholipases in steroidogenesis in the adrenal cortex.

Regulation of aldosterone synthesis and secretion

Aldosterone is a steroid hormone synthesized in and secreted from the outer layer of the adrenal cortex, the zona glomerulosa. Aldosterone is responsible for regulating sodium homeostasis, thereby helping to control blood volume and blood pressure. Insufficient aldosterone secretion can lead to hypotension and circulatory shock, particularly in infancy. On the other hand, excessive aldosterone levels, or those too high for sodium status, can cause hypertension and exacerbate the effects of high blood pressure on multiple organs, contributing to renal disease, stroke, visual loss, and congestive heart failure. Aldosterone is also thought to directly induce end-organ damage, including in the kidneys and heart. Because of the significance of aldosterone to the physiology and pathophysiology of the cardiovascular system, it is important to understand the regulation of its biosynthesis and secretion from the adrenal cortex. Herein, the mechanisms regulating aldosterone production in zona glomerulosa cells are discussed, with a particular emphasis on signaling pathways involved in the secretory response to the main controllers of aldosterone production, the renin-angiotensin II system, serum potassium levels and adrenocorticotrophic hormone. The signaling pathways involved include phospholipase C-mediated phosphoinositide hydrolysis, inositol 1,4,5-trisphosphate, cytosolic calcium levels, calcium influx pathways, calcium/calmodulin-dependent protein kinases, diacylglycerol, protein kinases C and D, 12-hydroxyeicostetraenoic acid, phospholipase D, mitogen-activated protein kinase pathways, tyrosine kinases, adenylate cyclase, and cAMP-dependent protein kinase. A complete understanding of the signaling events regulating aldosterone biosynthesis may allow the identification of novel targets for therapeutic interventions in hypertension, primary aldosteronism, congestive heart failure, renal disease, and other cardiovascular disorders.

Vascular Endothelial Growth Factor-A and Aldosterone

Aldosterone levels are markedly elevated during normal pregnancy but fall even though volume contracts when preeclampsia occurs. The level of aldosterone in either condition cannot be explained solely by the activity of the renin–angiotensin II system. In normal gestation, vascular endothelial growth factor (VEGF) is thought to maintain vascular health, but its role in adrenal hormone production is unknown. We hypothesized that the role of VEGF in the adrenal gland is to maintain vascular health and regulate aldosterone production. Here, we demonstrate that supernatant of endothelial cells grown in the presence of VEGF enhanced aldosterone synthase activity in human adrenocortical cells. VEGF either alone or combined with angiotensin II increased aldosterone production in adrenal cells. These data suggest that endothelial cell–dependent and independent activation of aldosterone is regulated by VEGF. In contrast to angiotensin II, VEGF did not upregulate the steroidogenic acute regulatory protein. Consistent with this observation, angiotensin II stimulated both aldosterone and cortisol synthesis from progesterone, whereas VEGF stimulated selectively aldosterone production. In rats, overexpression of soluble fms-like tyrosine kinase-1, an endogenous VEGF inhibitor, led to adrenocortical capillary rarefaction and fall in aldosterone concentrations that correlated inversely with soluble fms-like tyrosine kinase-1 levels. These findings may explain why aldosterone increases so markedly during normal gestation and why preeclampsia, a condition characterized by high soluble fms-like tyrosine kinase-1, is associated with inappropriately low aldosterone levels in spite of relatively lower plasma volumes.

Interaction between the heme oxygenase system and aldosterone in hypertension

The chronic intraperitoneal administration of the heme oxygenase inducer, hemin (15 mg/kg daily), for three weeks reduced blood pressure in adult spontaneously hypertensive rats (SHR) from 210.1±1.03 mmHg to 127±0.9 mmHg (n=10, P<0.01) but had no effect on age-matched normotensive Wistar-Kyoto or Sprague-Dawley strains. The antihypertensive effect of hemin was accompanied by reduced expression of aldosterone synthase messenger RNA and depleted levels of plasma aldosterone (675.7±121.6 pg/mL versus 365.7±37 pg/mL; n=4, P<0.05).Because aldosterone is known to stimulate phospholipase C (PLC), the effect of hemin on PLC was examined. Hemin abated PLC activity (29.6±1.5 nmol/min/mL versus 3.1±0.9 nmol/min/mL; n=5, P<0.01) and this was accompanied by depleted levels of intracellular calcium (551±46 nM versus 103.2±6.3 nM; n=4, P<0.01) in the aorta of SHR. In contrast, enhanced heme oxygenase activity and elevated cyclic GMP levels (17.74±0.08 pmol/mg versus 30.4±2.3 pmol/mg protein; n=6, P<0.01) were detected in hemin-treated SHR. Additionally, hemin therapy also suppressed inflammatory and oxidative insults by significantly reducing nuclear factor kappa B messenger RNA expression while enhancing the total antioxidant capacity (0.22±0.02 Trolox equivalent antioxidant capacity (TEA C)/mg protein versus 0.60±0.04 TEA C/mg protein; n=4, P<0.01).The concomitant depletion of aldosterone, PLC activity, intracellular calcium and the corresponding decline of inflammatory and oxidative insults may account for the antihypertensive effects of hemin.

Angiotensin II receptors mediate increased distal nephron acidification caused by acid retention

Patients with a moderately reduced glomerular filtration rate (GFR) typically have no metabolic acidosis and a urine net acid excretion comparable to those with normal GFR, supporting greater per nephron acidification with moderately reduced GFR. We modeled such patients using rats with a surgical reduction of 2/3 kidney mass, yielding animals with reduced GFR without metabolic acidosis. We then tested the hypothesis that reduction of nephron mass augments distal nephron acidification in remnant nephrons mediated by increased angiotensin II activity, and that the latter is induced by underlying acid retention. Nephron mass reduction yielded lower GFR than controls (sham operation), higher acid retention (measured by microdialysis of kidney cortex), higher distal nephron acidification, and higher plasma and kidney levels of angiotensin II, but plasma total CO(2) and urine net acid excretion were not different. Angiotensin II receptor antagonism reduced distal nephron acidification to levels similar to control. Dietary alkali that lowered acid retention to that of control also reduced plasma and kidney levels of angiotensin II and reduced distal nephron acidification to control. Angiotensin II receptor antagonism with dietary alkali had no significant added effect on distal nephron acidification. Thus, nephron reduction that moderately reduced GFR with no metabolic acidosis is characterized by increased angiotensin II activity. This mediates increased distal nephron acidification and is induced by acid retention.

Physiology of endothelin and the kidney

Since its discovery in 1988 as an endothelial cell-derived peptide that exerts the most potent vasoconstriction of any known endogenous compound, endothelin (ET) has emerged as an important regulator of renal physiology and pathophysiology. This review focuses on how the ET system impacts renal function in health; it is apparent that ET regulates multiple aspects of kidney function. These include modulation of glomerular filtration rate and renal blood flow, control of renin release, and regulation of transport of sodium, water, protons, and bicarbonate. These effects are exerted through ET interactions with almost every cell type in the kidney, including mesangial cells, podocytes, endothelium, vascular smooth muscle, every section of the nephron, and renal nerves. In addition, while not the subject of the current review, ET can also indirectly affect renal function through modulation of extrarenal systems, including the vasculature, nervous system, adrenal gland, circulating hormones, and the heart. As will become apparent, these pleiotropic effects of ET are of fundamental physiologic importance in the control of renal function in health. In addition, to help put these effects into perspective, we will also discuss, albeit to a relatively limited extent, how alterations in the ET system can contribute to hypertension and kidney disease.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

Heme-arginate suppresses phospholipase C and oxidative stress in the mesenteric arterioles of mineralcorticoid-induced hypertensive rats

Induction of heme-oxygenase (HO) is an important cellular defense mechanism against oxidative and inflammatory insults. We analyzed the effects of the HO inducer, heme-arginate, on the phospholipase C (PLC)/inositol-triphosphate (IP(3)) pathway in the mesenteric arterioles of uninephrectomized (UnX) deoxycorticosterone acetate (DOCA)-salt hypertensive rats, which is a volume-overload model characterized by elevated endothelin (ET-1) and mineralocorticoid-induced oxidative/inflammatory insults. Our study included the following groups: (A) controls [(i) surgery-free Sprague-Dawley (SD) rats, (ii) UnX-Sham, (iii) UnX-Salt (0.9% NaCl+0.2% KCl) and (iv) UnX-DOCA)]; (B) UnX-DOCA-salt hypertensive rats; (C) UnX-DOCA-salt+heme-arginate; (D) UnX-DOCA-salt+heme-arginate+chromium mesoporphyrin (CrMP), the HO inhibitor; (E) UnX-DOCA-salt+CrMP (F); SD+heme-arginate, (G) UnX-DOCA-salt+vehicle dissolving heme-arginate and CrMP and (H) normal-SD+heme-arginate. Quantitative reverse transcriptase PCR, western blot, enzyme immunoassay and spectrophotometric analyses were used. Heme-arginate enhanced mesenteric arteriole HO-1, HO activity, cyclic guanosine monophosphate (cGMP) and anti-oxidants including bilirubin, ferritin, superoxide dismutase with potentiation of the total anti-oxidant capacity. Correspondingly, oxidative/inflammatory mediators such as 8-isoprostane, nuclear-factor kappaB (NF-kappaB) and ET-1 were markedly reduced. Furthermore, heme-arginate suppressed PLC activity, attenuated IP(3) and reduced resting intracellular calcium. The effects of heme-arginate were nullified by the HO inhibitor, with aggravation of oxidative/inflammatory insults. In heme-arginate-treated SD rats, the HO system was potentiated to a lesser magnitude and the suppression of ET-1, PLC, IP(3) and NF-kappaB were less accentuated, suggesting greater selectivity of HO against the ET-1-PLC-IP(3)-NF-kappaB destructive axis in the pathological condition of mineralocorticoid-induced hypertension. Given that ET-1 stimulates PLC and IP(3), which in turn activates NF-kappaB, the concomitant reduction of ET-1, PLC, IP(3) and NF-kappaB alongside the corresponding decline of resting intracellular calcium may account for the reduction of blood pressure and attenuation of oxidative/inflammatory injury by heme-arginate.

Crosstalk between the heme oxygenase system, aldosterone, and phospholipase C in hypertension

BACKGROUND

Aldosterone is a mineral corticoid hormone that is produced in response to angiotensin-II, and like angiotensin-II, stimulates inflammation, oxidative stress, and fibrosis by activating nuclear factor-kappaB and activating protein-1. Recent evidence, however, indicates that aldosterone stimulates phospholipase C and activates nuclear factor-kappaB and activating protein-1. Although the heme oxygenase system is cytoprotective, its effects on aldosterone-phospholipase C signaling in deoxycorticosterone acetate (DOCA-salt) hypertension, a model of aldosteronism, and spontaneously hypertensive rat, a genetic model of human essential hypertension, have not been fully characterized.

METHODS

In the present study, the heme oxygenase inducer, hemin, was given to spontaneously hypertensive and deoxycorticosterone acetate hypertensive rats, and the effects on blood pressure, aldosterone, nuclear factor-kappaB, activating protein-1, phospholipase C, and inositol 1,4,5-triphosphate were examined.

RESULTS

Hemin therapy restored physiological blood pressure to spontaneously hypertensive rats (209.9 +/- 0.9 to 127.3 +/- 0.85 mmHg, n = 10, P < 0.01) and to deoxycorticosterone acetate salt hypertensive rats (195.7 +/- 1.8 vs.132.5 +/- 2.1 mmHg; P < 0.01, n = 10), but had no effect on age-matched normotensive Wistar-Kyoto or Sprague-Dawley strains. The antihypertensive effect was accompanied by enhanced heme oxygenase activity, upregulated cyclic guanosine monophosphate-protein kinase G signaling, increased superoxide dismutase activity, and the potentiation of total antioxidant capacity, whereas aldosterone, activating protein-1, and nuclear factor-kappaB were reduced. Furthermore, hemin suppressed phospholipase C activity, attenuated inositol 1,4,5-triphosphate, and reduced resting intracellular calcium in the aorta.

CONCLUSION

Collectively, our results suggest that the concomitant depletion of aldosterone, phospholipase C-inositol 1,4,5-triphosphate activity, resting intracellular calcium and the corresponding decline of inflammatory, and oxidative insults may account for the antihypertensive effects of hemin in deoxycorticosterone acetate hypertension and spontaneously hypertensive rats.

Modulation of pulmonary endothelial endothelin B receptor expression and signaling: implications for experimental hepatopulmonary syndrome

The hepatopulmonary syndrome (HPS) results from intrapulmonary vasodilation in the setting of cirrhosis and portal hypertension. In experimental HPS, pulmonary endothelial endothelin B (ET(B)) receptor overexpression and increased circulating endothelin-1 (ET-1) contribute to vasodilation through enhanced endothelial nitric oxide synthase (eNOS)-derived nitric oxide (NO) production. In both experimental cirrhosis and prehepatic portal hypertension, ET(B) receptor overexpression correlates with increased vascular shear stress, a known modulator of ET(B) receptor expression. We investigated the mechanisms of pulmonary endothelial ET(B) receptor-mediated eNOS activation by ET-1 in vitro and in vivo. The effect of shear stress on ET(B) receptor expression was assessed in rat pulmonary microvascular endothelial cells (RPMVECs). The consequences of ET(B) receptor overexpression on ET-1-dependent ET(B) receptor-mediated eNOS activation were evaluated in RPMVECs and in prehepatic portal hypertensive animals exposed to exogenous ET-1. Laminar shear stress increased ET(B) receptor expression in RPMVECs without altering mRNA stability. Both shear-mediated and targeted overexpression of the ET(B) receptor enhanced ET-1-mediated ET(B) receptor-dependent eNOS activation in RPMVECs through Ca(2+)-mediated signaling pathways and independent of Akt activation. In prehepatic portal hypertensive animals relative to control, ET-1 administration also activated eNOS independent of Akt activation and triggered HPS. These findings support that increased pulmonary microvascular endothelial ET(B) receptor expression modulates ET-1-mediated eNOS activation, independent of Akt, and contributes to the development of HPS.

Endothelin role in kidney acidification

Endothelin is a potent vasoconstrictor that recent studies show modulates transport in kidney tubules, including that related to acidification. The data support a physiologic role for endothelin in mediating enhanced kidney tubule acidification in response to an acid challenge to systemic acid-base balance status. The data to date do not support an endothelin role in maintaining kidney tubule acidification in control, nonacid-challenged states. Endothelin also contributes to the enhanced acidification of some pathophysiologic states and might have a role in some of the untoward outcomes associated with these conditions. This reviews supports continuation of studies into the physiologic and possibly pathophysiologic role of endothelin in settings of increased tubule acidification.

Regulation of kidney acid excretion by endothelins

Endothelin (ET) is a potent vasoconstrictor that is now known to modulate kidney tubule transport, including kidney tubule acidification. Animals undergoing an acid challenge to systemic acid-base status and with some models of chronic metabolic acidosis have increased kidney ET production. Increased ET production/activity contributes to enhanced kidney tubule acidification that facilitates kidney acid excretion in response to an acid challenge to systemic acid-base status. The data to date support a physiologic role for ET in mediating enhanced kidney acidification in response to acid challenges, but do not support an ET role in maintaining kidney tubule acidification in control, non-acid-challenged states. ET increases acidification in both the proximal and distal nephron and appears to exert its effects both directly and indirectly, the latter through modulating the levels and/or activity or other mediators of kidney tubule acidification. ET also contributes to enhanced kidney acidification in some pathophysiologic states and might contribute to some untoward outcomes associated with these conditions. Whether ET should be a therapeutic target in treating and/or preventing some of these untoward outcomes remains an open question. This review supports continued research into the physiologic and possibly pathophysiologic role of ET in settings of increased kidney tubule acidification.

Mechanisms of endothelin-1-induced MAP kinase activation in adrenal glomerulosa cells

G protein-coupled receptors (GPCRs) such as angiotensin II, bradykinin and endothelin-1 (ET-1) are critically involved in the regulation of adrenal function, including aldosterone production from zona glomerulosa cells. Whereas, substantial data are available on the signaling mechanisms of ET-1 in cardiovascular tissues, such information in adrenal glomerulosa cells is lacking. Bovine adrenal glomerulosa (BAG) cells express receptors for endothelin-1 (ET-1) and their stimulation caused phosphorylation of Src (at Tyr416), proline-rich tyrosine kinase (Pyk2 at Tyr402), extracellularly regulated signal kinases (ERK1/2), and their dependent proteins, p90 ribosomal S6 kinase (RSK-1) and CREB. ET-1 elicited these responses predominantly through activation of a G(i)-linked cascade with a minor contribution from the G(q)/PKC pathway. Whereas, selective inhibition of EGF-R kinase with AG1478 caused complete inhibition of EGF-induced ERK/RSK-1/CREB activation, it caused only partial reduction (30-40%) of such ET-1-induced responses. Consistent with this, inhibition of matrix metalloproteinases (MMPs) with GM6001 reduced ERK1/2 activation by ET-1, consistent with partial involvement of the MMP-dependent EGF-R activation in this cascade. Activation of ERK/RSK-1/CREB by both ET-1 and EGF was abolished by inhibition of Src, indicating its central role in ET-1 signaling in BAG cells. Moreover, the signaling characteristics of ET-1 in cultured BAG cells closely resembled those observed in clonal adrenocortical H295R cells. The ET-1-induced proliferation of BAG and H295 R cells was much smaller than that induced by Ang II or FGF. These data demonstrate that ET-1 causes ERK/RSK-1/CREB phosphorylation predominantly through activation of G(i) and Src, with a minor contribution from MMP-dependent EGF-R transactivation.

Activation of endothelinA receptors in frog adrenocortical cells stimulates both calcium mobilization from intracellular stores and calcium influx through L-type calcium channels

We have previously shown that endothelin (ET)-1 stimulates corticosterone and aldosterone secretion by the frog adrenal gland through activation of ETA receptors positively coupled to both the adenylyl cyclase and phospholipase C (PLC) pathways. The purpose of the present study was to investigate the involvement of calcium in ET-1-induced stimulation of corticosteroid secretion. Cytoautoradiographic labeling using [125I]ET-1 as a tracer revealed the presence of ET-1 binding sites on adrenocortical cells. Administration of graded concentrations of ET-1 in the vicinity of adrenocortical cells provoked a dose-dependent increase in cytosolic calcium concentrations ([Ca2+]i). ET-1 induced a biphasic response consisting of an immediate and transient peak of [Ca2+]i followed by a plateau phase. Preincubation of the cells with the calcium-ATPase inhibitor thapsigargin or the PLC inhibitor U-73122 reduced the amplitude of the transient phase. Administration of the calcium chelator EGTA or the protein kinase A inhibitor H-89 attenuated the plateau phase. The [Ca2+]i response to ET-1 was markedly reduced during concomitant administration of U-73122 and H-89. Preincubation of the cells with the L-type calcium channel blocker nifedipine attenuated the plateau phase. Corticosteroid secretion from perifused frog adrenal slices was almost completely suppressed by thapsigargin and reduced by nifedipine. Taken together, these data indicate that activation of ETA receptors in frog adrenocortical cells provokes immediate stimulation of PLC, which causes an early mobilization of calcium from intracellular stores, and activates adenylyl cyclase, which results in delayed calcium influx through L-type calcium channels. The resulting increase in [Ca2+]i plays a pivotal role in ET-1-induced corticosteroid secretion.

Effects of peptides, with emphasis on feeding, pain, and behavior A 5-year (1999-2003) review of publications in Peptides

Novel effects of naturally occurring peptides are continuing to be discovered, and their mechanisms of actions as well as interactions with other substances, organs, and systems have been elucidated. Synthetic analogs may have actions similar or antagonistic to the endogenous peptides, and both the native peptides and analogs have potential as drugs or drug targets. The journal Peptides publishes many leading articles on the structure-activity relationship of peptides as well as outstanding reviews on some families of peptides. Complementary to the reviews, here we extract information from the original papers published during the past five years in Peptides (1999-2003) to summarize the effects of different classes of peptides, their modulation by other chemicals and various pathophysiological states, and the mechanisms by which the effects are exerted. Special attention is given to peptides related to feeding, pain, and other behaviors. By presenting in condensed form the effects of peptides which are essential for systems biology, we hope that this summary of existing knowledge will encourage additional novel research to be presented in Peptides.

The endothelin system and its role in acute myocardial infarction

Immediately after an acute myocardial infarction (AMI) or in models of ischemia-reperfusion injury, cardiac endothelin (ET) system is markedly activated, and plasma levels of ET are increased. In the heart, expression of the main components of the ET system (ET-1 peptide, both receptor subtypes ETA and ETB, though not endothelin converting enzyme) are increased both at the gene level and protein level, in the viable myocardium, and--even more substantially--in the necrotic area. Despite these conspicuous abnormalities, the role of ET in this setting remains unclear. In the absence of human data, most short-term studies in animals (in terms of hours to up to 8 days post-AMI) and in the reperfused ischemic heart, have found beneficial effects of ET receptor blockade on survival rate, incidence of arrhythmias, cardiac function, and morphology. In contrast, many studies in which a long-term ET inhibition was started immediately post-infarction and the late effects were examined in animals with ensuing chronic heart failure (14-100 days postinfarction), adverse effects were also observed, such as scar thinning, further ventricular dilation, or even a worse survival rate. It appears that the ET system plays a dual role during the early post-AMI period. At present, it is not clear whether the short-term beneficial effects or long-term adverse effects of ET receptor blockade would prevail. Acute use of short-acting ET receptor antagonists in patients with AMI complicated by an acute heart failure is an attractive possibility that also remains to be investigated.

Aldosterone as a target in congestive heart failure

Based upon the results of the RALES trial and accumulating evidence about the role of aldosterone and aldosterone receptor antagonism in various disease states, the authors anticipate that aldosterone receptor antagonists will become standard therapy, along with ACE inhibitors and beta-adrenergic receptor blocking agents, in patients with heart failure that is caused by systolic left ventricular dysfunction. Furthermore, the prospect of the use of these agents in other disease states that have implicated an activated rennin-angiotensin-aldosterone cascade, such as diastolic dysfunction, aging, and atherosclerosis, remains to be tested. Until further data from well-designed, prospective, randomized trials are available, the use of aldosterone receptor antagonists should be restricted to patients with severe or progressive heart failure caused by systolic left ventricular dysfunction in whom serum creatinine level is < or = 2.0 mg/dL and serum potassium levels are < 5.0 meq/L at baseline.

Mechanisms transducing the aldosterone secretagogue signal of endothelins in the human adrenal cortex

Evidence has been provided that the 21-amino acid hypertensive peptide endothelin (ET)-1 exerts a potent secretagogue effect on human adrenocortical zona glomerulosa (ZG), acting through two receptor subtypes, called ET(A) and ET(B), the signaling mechanism(s) of which has (have) not yet been investigated. Collagenase dispersed human ZG cells were obtained from normal adrenals of patients undergoing nephrectomy/adrenalectomy for renal cancer. The selective ET(A)- and ET(B)-receptor activation was obtained by exposing dispersed cells to ET-1 plus the ET(B)-receptor antagonist BQ-788 and to the ET(B)-receptor agonist BQ-3020, respectively. The phospholipase (PL) C inhibitor U-73122 abolished ET(A) receptor-mediated secretory response, but only partially prevented the ET(B) receptor-mediated one. The phosphatidylinositol 3-kinase inhibitor wortmannin, the calmodulin inhibitor W-7 and the protein kinase (PK) C inhibitor calphostin-C significantly blunted the secretory responses ensuing from the activation of both receptor subtypes. When added together, calphostin-C and wortmannin or W-7 abolished ET(A)-mediated secretory response, but only decreased ET(B)-mediated one. The ET(B) receptor-, but not the ET(A) receptor-mediated aldosterone response was partially reversed by the cyclooxygenase (COX) inhibitor indomethacin, which when added together with U-73122 abolished it. ET(A)-receptor activation raised inositol triphosphate (IP(3)) production from dispersed ZG cells, while ET(B)-receptor stimulation enhanced both IP(3) and prostaglandin-E(2) production. Collectively, our findings indicate that ETs stimulate aldosterone secretion from human ZG cells, acting through ET(A) receptors exclusively coupled to PLC/PKC-dependent pathway and ET(B) receptors coupled to both PLC/PKC- and COX-dependent cascades.

Endothelin in health and disease: endothelin receptor antagonists in the management of pulmonary artery hypertension

Endothelin (ET) has been identified as playing a fundamental role in many disease processes. Therapeutic efforts at interrupting ET's pathologic effects have focused on endothelin receptor antagonists (ERAs), of which two, bosentan and sitaxsentan, have been evaluated for the treatment of both primary and secondary pulmonary arterial hypertension (PAH). We discuss the multiple actions of ET, its role in various disease states, and the effects of ET receptor stimulation and blockade. Current classification and management of PAH are reviewed, along with the promise of greatly improved treatment generated by recent and ongoing clinical trials using ERAs.