Abstract P3124: Chronic Infusion Of Angiotensin II Promotes Ventricular Fibrosis And Diastolic Dysfunction In Aging Male But Not Female Mouse Hearts

Abstract

Heart failure prevalence increases with age and affects men and women differently. Chronic activation of the renin-angiotensin system (RAS) in heart failure increases circulating angiotensin II (AII) levels, which elevates blood pressure (BP), promotes fibrosis and leads to adverse remodelling of the heart. Whether maladaptive responses to AII differ between the sexes at older ages is unclear, as most studies use young male animal models. We investigated whether adverse cardiac remodeling induced by chronic exposure to AII differed between the sexes in older C57BL/6 mice. Osmotic minipumps with pressor doses of AII (3 mg/kg/day) or saline were implanted into older mice (≈16 mos) of both sexes for 6 weeks. BP (tail cuff) and ventricular structure/function (echocardiography) were measured at baseline, midpoint, and endpoint. Ventricular fibrosis markers (transforming growth factor-ß (TGF-ß), fibronectin collagen I, collagen III) were quantified with qPCR. Mean arterial pressure increased similarly in both sexes (76.3±4.2 vs. 136.1±4.6 mmHg in males and 73.9±2.9 vs. 116.1±8.7 mmHg in females; p<0.05; n=6-8/group). AII infusion also increased LV mass and reduced ejection fraction in males and females. By contrast, AII increased signs of diastolic dysfunction in males but had little impact on diastolic function in females. For example, isovolumic relaxation time increased over 6 weeks of AII infusion in males (11.7±1.0 vs. 19.0±1.4 ms; p<0.05) but not in females (14.6±0.9 vs. 16.4±1.2 ms). Similar results were seen for E/A ratios. Molecular studies showed a marked increase in mRNA abundance for TGF-ß in male ventricles (1.02±0.13 vs. 1.50±0.16; p<0.05) but not in females (1.01±0.08 vs. 1.25±0.10). Similar male-female differences were seen for collagens I and III (fibronectin was similar in both sexes, and not affected by AII). As TGF-ß signalling increases the production of profibrotic mediators like collagens I and III, these findings suggest that chronic RAS activation increases fibrosis and disrupts diastolic function in aging male hearts. By contrast, older female hearts are resistant to these deleterious effects of RAS activation. These sex-specific differences may modify heart failure expression and responses to treatment in older men and women.