Uninephrectomized rats drinking 1% sodium chloride were given aldosterone (Aldo, 0.75 gg/h, subcutaneous Is.c.I infusion), deoxycorticosterone (DOC, 20 mg/wk, s.c.), corticosterone (B, 2 mg/d, s.c.), or the antiglucocorticoid-antiprogestin RU486 (2 mg/d, s.c.) for 8 wk, and hemodynamic and tissue responses were compared with a non-steroid-treated control group. Aldo and DOC markedly increased systolic BP and caused considerable (40-50%) cardiac hypertrophy; B and RU486 caused neither hypertension nor cardiac hypertrophy. Measurements of ventricular cross-sectional areas showed hypertrophy due to an increase in mass of the left ventricle only. Cardiac hydroxyproline concentration was increased considerably by Aldo and DOC, to a lesser degree by RU486, and not by B. Aldo markedly elevated left ventricular interstitial collagen (2.5-fold vs control, P < 0.01 vs all groups); other steroid treatments also increased interstitial collagen over control (DOC X 1.8-, RU486 X 1.6-, B X 13-fold), with identical responses for right and left ventricles (r = 0.94). A different pattern of perivascular fibrosis was noted; DOC elevated perivascular collagen (2.1-fold vs control, P < 0.01 vs all other groups); RU486 raised levels 1.4-fold vs control, but neither Aldo nor B significantly affected perivascular collagen. These data are consistent with interstitial cardiac fibrosis reflecting type I (mineralocorticoid) receptor occupancy by administered Aldo or DOC, or by elevated endogenous B after type II (glucocorticoid) receptor blockade after RU486 administration; perivascular fibrosis may reflect a composite response after type I receptor agonist/type II glucocorticoid receptor antagonist occupancy. (J. Clin. Invest. 1994.93:2578-2583
Abstract-Increased mineralocorticoid levels plus high salt promote vascular inflammation and cardiac tissue remodeling.Mineralocorticoid receptors are expressed in many cell types of the cardiovascular system, including monocytes/macrophages and other inflammatory cell types. Although mineralocorticoid receptors are expressed in monocytes/macrophages, their role in regulating macrophage function to date has not been investigated. We, thus, used the Cre/LoxP-recombination system to selectively delete mineralocorticoid receptors from monocytes/macrophages with the lysozyme M promoter used to drive Cre expression (MR flox/flox /LysM Cre/Ϫ mice). Male mice from each genotype (MR flox/flox or wild-type and MR flox/flox /LysM Cre/Ϫ mice) were uninephrectomized, given 0.9% NaCl solution to drink, and treated for 8 days or 8 weeks with either vehicle (nϭ10) or deoxycorticosterone (nϭ10). Equivalent tissue macrophage numbers were seen for deoxycorticosterone treatment of each genotype at 8 days; in contrast, plasminogen activator inhibitor type 1 and NAD(P)H oxidase subunit 2 levels were increased in wild-type but not in MR flox/flox / LysM Cre/Ϫ mice given deoxycorticosterone. Baseline expression of other inflammatory genes was reduced in MR flox/flox /LysM Cre/Ϫ mice compared with wild-type mice. At 8 weeks, deoxycorticosterone-induced macrophage recruitment and connective tissue growth factor and plasminogen activator inhibitor type 1 mRNA levels were similar for each genotype; in contrast, MR flox/flox /LysMCre/Ϫ mice showed no increase in cardiac fibrosis or blood pressure, as was seen in wild-type mice at 8 weeks. These data demonstrate the following points: (1) mineralocorticoid receptor signaling regulates basal monocyte/macrophage function; (2) macrophage recruitment is not altered by loss of mineralocorticoid receptor signaling in these cells; and (3) a novel and significant role is seen for macrophage signaling in the regulation of cardiac remodeling and systolic blood pressure in the deoxycorticosterone/salt model. T he clinical use of mineralocorticoid receptor (MR) antagonists added to the current standard of care reduces morbidity and mortality in patients with congestive heart failure 1,2 and reduces blood pressure and proteinuria as monotherapy in essential hypertension. 3 Although the precise mechanism for this protection remains to be determined, considerable insights have been obtained from experimental models of mineralocorticoid/salt-mediated cardiac fibrosis 4 -6 ; hypertension, cardiac hypertrophy, and fibrosis are key responses to the administration of aldosterone or deoxycorticosterone (DOC) concurrently with a high salt intake for 8 weeks. Importantly, the pathogenesis of cardiac fibrosis is independent of hypertension and cardiac hypertrophy in this model, suggesting a direct role for MR activation in driving the onset and progression of cardiovascular disease. 4 -6 We and others have previously identified vascular inflammation (ie, osteopontin and plasminogen activator inhibitor type 1 [PA...
Abstract-Sodium transport in epithelial tissues is regulated by the physiological mineralocorticoid aldosterone. The response to aldosterone is mediated by the mineralocorticoid receptor (MR), for which the crystal structure of the ligand-binding domain has recently been established. The classical mode of action for this receptor involves the regulation of gene transcription. Several genes have now been shown to be regulated by aldosterone in epithelial tissues. Of these, the best characterized is serum-and glucocorticoid-regulated kinase, which increases sodium influx through the epithelial sodium channel. Turnover of these channels in the cell membrane is mediated by Nedd4 -2, a ubiquitin protein ligase; serum-and glucocorticoid-regulated kinase interacts with and phosphorylates Nedd4 -2, thereby rendering it unable to bind the sodium channels. Key Words: aldosterone Ⅲ sodium channels Ⅲ fibrosis T he isolation of aldosterone just over 50 years ago established it as the primary physiological mineralocorticoid. 1 Sodium transport, and hence salt balance, is regulated by a number of mechanisms; however, aldosterone has a critical role. Aldosterone exerts its effects on the distal nephron (and colon) as the last point of sodium reabsorption; it is thus the final arbiter. 2,3 The importance of aldosterone in the maintenance of sodium homeostasis is seen in a series of monogenetic causes of hypertension, 2 in Conn's syndrome, and in disorders in which mineralocorticoid action is compromised with consequent, life-threatening salt losses. 3 Although other pathophysiological consequences of aldosterone excess were identified by Selye 4 over 60 years ago, their significance has only recently been appreciated. Evidence from the Randomized ALdactone Evaluation Study (RALES) and EPlerenone neuroHormonal Efficacy and SUrvival Study (EPHESUS) trials of beneficial effects of mineralocorticoid antagonist therapy on morbidity and mortality in cardiac failure has focused attention beyond the kidney to effects of mineralocorticoids more broadly in the cardiovascular system. 5 Although an understanding of the molecular basis of aldosterone action has tended to lag behind advances in the biology of other steroid hormones, the last decade has seen significant advances toward an understanding of the mechanisms of mineralocorticoid action. The primary mediator of the response to aldosterone is the mineralocorticoid receptor (MR), the ligand-binding domain (LBD) of which has been recently crystallized. 6 -8 Although the MR primarily acts as a transcription factor, recent evidence suggests that it may also mediate nongenomic (or nonnuclear) activation of second messenger pathways. In addition, there is a growing body of evidence that some actions of aldosterone may involve a receptor other than the MR. The cellular and molecular mediators, including proteins induced by aldosterone, have been characterized in sodium transporting epithelia; however, the critical molecular events in the vasculature remain to be determined. In this brief r...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.