Altered Ca(2+) homoeostasis accompanies
heart failure. As a model of
heart failure, transgenic mice (TG) with selective overexpression of
calsequestrin (CSQ) in the heart were used. CSQ is the main Ca(2+)
binding protein in the lumen of the junctional sarcoplasmic reticulum. Overexpression of CSQ leads to
hypertrophy,
fibrosis,
heart failure,
cardiac arrhythmias, and ultimately premature death compared to littermate controls (WT). In the present study,
cardiac hypertrophy was noted at 2 months of age (relative heart weight 6.4 +/- 0.2 mg/g in WT and 11.2 +/- 0.3 mg/g in TG, n = 7, p < 0.05) which progressed at 5 months of age (relative heart weight 15.5 +/- 1.1 mg/g in TG, n = 11). Furthermore, an increased degree of
fibrosis (from 0.29 +/- 0.04 in WT to 0.77 +/- 0.06 in TG, n = 8, p < 0.05) was quantified by sirius red staining. Cardiac function was greatly impaired in TG as exemplified by reduced pressure development and
cardiac arrhythmias. It is hypothesized that
losartan, an inhibitor of
angiotensin II receptors, might be able to attenuate these detrimental effects. Hence, TG and WT were treated for 1 or 4 months perorally with
losartan (5 mg/kg/day) or
solvent alone (control conditions) starting at 4 weeks of age. Under control conditions, none of the WT died within the observation period whereas all TG died within 9 months.
Losartan treatment reduced the mortality of TG: Mean life span was raised from 116 to 193 days (n = 18 end, p < 0.05). Likewise,
losartan reduced relative heart weight and the degree of
fibrosis. In addition,
losartan improved hemodynamic parameters, like left ventricular pressure and its first derivative. However,
losartan treatment did not modify overexpression of CSQ in the heart of TG. These results imply that the
angiotensin II receptor (type 1) contributes to
heart failure due to CSQ overexpression, as its blockade improved survival.