Proceedings of The Physiological Society
University of Manchester (2010) Proc Physiol Soc 19, PC181
Activation of macrophages is crucial for the loss of anticontractile capacity of perivascular fat following inflammation and can be rescued by eplerenone
N. Jakka1, S. B. Withers1, M. Werner1, A. M. Heagerty1
1. Cardiovascular research group, University of Manchester, Manchester, United Kingdom.
cGMP dependent protein kinase 1 (PKG-1) is an important signalling molecule in the nitric oxide pathway. Following activation it can cause smooth muscle relaxation through activation of BKca channels, inhibition of IP3 and phosphorylation of proteins including vasodilator-stimulated phosphoprotein (VASP) 1. The mineralocorticoid receptor antagonist eplerenone has also been shown to phosphorylate VASP at the same site as PKG. The aim of this study was to establish its role in the loss of the anticontractile effect of perivascular fat following hypoxia. The contractility of mesenteric arteries ± perivascular fat from PKG-1 knockout mice and wild type littermates was investigated using a wire myograph. Dose response curves to noradrenaline (NA) were performed before and after experimental hypoxia (2.5 hours, 95%N2/5%CO2) ± eplerenone (5µM). Contractile responses to NA were calculated as a percentage of KCl contraction and expressed as mean±SEM. Data were analysed using a two-way ANOVA, P<0.05 was taken as significant. Arteries ± fat from knockout mice constricted significantly more to NA than wild type littermates (No fat: P=0.048; Fat: P=0.019, n=3). Hypoxia caused an increase in contractility in wild type arteries with fat (P=0.04, n=3), but had no effect on the maximum level of constriction in knockout arteries (Normoxia: 145.8 ± 5.5% vs. hypoxia: 149.5 ± 8.4%, n=3) or arteries without fat. Eplerenone was associated with a reduction in constriction of both wild type and knockout arteries with fat to a similar level (WT: 108.5 ± 13.9% vs. KO 103.4 ± 10.0%, n=3). Arteries without fat from knockout mice incubated with eplerenone during hypoxia had a small but significant reduction in contractility (P=0.048), although there were no differences in wild type arteries. The anticontractile effect of perivascular fat is absent in PKG1 knockout mice, furthermore there is no increase in contractility following experimental hypoxia as observed in wild type littermates. Eplerenone is able to reverse the effects of hypoxia in wild type arteries with fat and reduces the contractility of arteries from knockout mice to a similar level suggesting that eplerenone works downstream of the PKG signalling event. The mechanism by which eplerenone causes its effects on contractility remains to be elucidated.
Where applicable, experiments conform with Society ethical requirements