The Role of the Glucocorticoid Receptor in Mineralocorticoid/Salt-Mediated Cardiac Fibrosis

Abstract

The pathophysiological consequences of excess mineralocorticoid for salt status include hypertension, vascular inflammation, and cardiac fibrosis. Mineralocorticoid receptor (MR) blockade can both prevent and reverse established inflammation and fibrosis due to exogenous mineralocorticoids or endogenous glucocorticoid activation of the MR. Glucocorticoids also exert potent antiinflammatory effects via glucocorticoid receptors (GR) in the vascular wall. We propose that GR signaling may ameliorate mineralocorticoid/salt-induced vascular inflammation and fibrosis in the mineralocorticoid/salt model. In the present study, the role of GR in the mineralocorticoid/salt model was explored in uninephrectomized rats that were maintained on 0.9% saline solution to drink and treated as follows: control (CON), no further treatment; deoxycorticosterone (DOC; 20 mg/wk) for 4 wk (DOC4); DOC for 8 wk (DOC8); DOC for 8 wk plus the GR antagonist RU486 (2 mg/d) wk 5-8 (DOC8/RU486); and DOC for 8 wk plus RU486 and the MR antagonist eplerenone (EPL; 50 mg/kg.d) for wk 5-8 (DOC8/RU486+EPL). DOC treatment significantly increased systolic blood pressure, cardiac fibrosis, inflammation (ED-1-positive macrophages and osteopontin), and mRNA for markers of oxidative stress (p22phox, gp91phox, and NAD(P)H-4). GR blockade reduced the DOC-mediated increase in systolic blood pressure and the number of infiltrating ED-1-positive macrophages but had no effect on fibrosis, oxidative stress, or osteopontin mRNA levels. EPL reversed DOC-induced pathology in the absence or presence of GR blockade. Thus, blocking agonist activity at the GR neither enhances nor attenuates the fibrotic response, although it may modulate systolic blood pressure and macrophage recruitment in the mineralocorticoid/salt model.