Effect of a Combined Treatment with Ivabradine and Spironolactone on Cardiac Structure and Function in Hypertensive Dahl Salt‐Sensitive Rats

Abstract

Introduction Hypertension-induced left ventricular (LV) hypertrophy and myocardial fibrosis provide structural basis for diastolic dysfunction. It has been previously reported that aldosterone receptor antagonist spironolactone (SL) can prevent myocardial fibrosis and, hence, alleviate hypertension-induced diastolic dysfunction, whereas treatment with heart rate lowering drug ivabradine (IVA) can improve cardiac function during development of hypertension-induced hypertrophy. Hypothesis We hypothesize that a combination of a heart rate-lowering drug IVA and a competitive mineralocorticoid receptor antagonist SL would alleviate adverse LV structural alterations and diastolic dysfunction in animals with chronic hypertension. Methods Seven-week-old, male Dahl salt-sensitive rats were fed a high-salt diet (8% NaCl) to induce sustained hypertension. After 7 weeks on a high-salt diet, in order to reduce the risk of death by stroke, the hypertensive (HT) rats were switched to a low-salt diet (0.3% NaCl) and randomly divided into two experimental groups: 1) treated with IVA (10 mg/kg/day) and SL (20 mg/kg/day) (HT-T) and 2) subjected to a vehicle only (HT-V). A mixture of dimethyl sulfoxide and propylene glycol (50%:50%, v/v) was used as a vehicle to deliver the drugs for 8 weeks by intraperitoneal ALZET osmotic pumps. The rats fed a low-salt diet only were used as an age-matched normotensive controls (NT). Heart rate and blood pressure were evaluated every week using the CODA tail-cuff plethysmography system. At the end of experiment, the hemodynamic parameters and LV function were assessed using a Millar micro-tip pressure catheter and a PowerLab data acquisition system. Subsequently, rats were euthanized, and their hearts were processed to paraffin for morphological evaluation. Serial sections from each heart were stained with various histological techniques. Images were captured using either a MicroScan D2 slide scanner or a Leica DM IRE2 microscope and analyzed by Image-Pro Analyzer v.7.0 software. Statistical analysis was performed using Prism 6 software. Results At the beginning of treatment, HT rats demonstrated a 42.3% increase in mean arterial blood pressure (MAP) and a 17.1% rise in heart rate compared to NT rats. During 8 weeks of treatment, the MAP remained comparably elevated in both HT groups, whereas heart rate had been persistently reduced in treated rats on average by 37.5% and 26.9% in comparison with HT-V and NT rats, respectively. At the end of a treatment period, rats in both HT groups had a significantly increased Tau constant, suggesting an analogous impairment of active relaxation. At the same time, all groups showed a similar level of LV end-diastolic pressure, indicating a preservation of passive myocardial stiffness. The examination of hearts has confirmed that chronic hypertension caused significant LV hypertrophy (P≤0.001) and myocardial fibrosis (P≤0.01) compared to NT rats. More important, HT rats in treated group revealed more pronounced concentric hypertrophy than animals in HT-V group. Conclusion Our findings establish that a combined treatment with IVA and SL augmented concentric LV hypertrophy and did not alleviate the hypertension-induced diastolic dysfunction.