Cardiac microvascular rarefaction in hyperthyroid rats is reversed by losartan, diltiazem, and propranolol

Cardiac microvascular rarefaction appears to be involved in hyperthyroidism-induced left ventricular hypertrophy and dysfunction. We investigated the effects of losartan, an AT1 receptor antagonist; diltiazem, a calcium channel blocker; and propranolol, a β-adrenergic receptor antagonist, on cardiac function and structural microcirculatory cardiac alterations in an experimental model of l-thyroxin-induced hyperthyroidism in rats. Hyperthyroidism (HYPER) was induced by intraperitoneal injections of l-thyroxin for 35 days (600 μg/kg/day; n = 32). The euthyroid group was treated with distilled water (EUT + VEH; n = 8). On the 14th day, the HYPER group was divided into four groups that received an oral treatment for 21 days with saline (HYPER + VEH; n = 8), losartan (10 mg/kg/day; HYPER + LOS, n = 8), diltiazem (10 mg/kg/day; HYPER + DILT, n = 8), or propranolol (10 mg/kg/day; HYPER + PROP, n = 8). An echocardiographic study was performed at baseline, at the beginning and at the end of the pharmacological treatment protocol (35th day). The structural capillary density in the left ventricle (LV) was analyzed using histochemical analysis with fluorescein isothiocyanate-conjugated Griffonia simplicifolia lectin. HYPER + VEH (182 ± 5 mmHg; P < 0.001) presented higher systolic blood pressure (SBP) compared with EUT + VEH (132 ± 3 mmHg). HYPER + LOS (144 ± 2 mmHg), HYPER + DILT (147 ± 3 mmHg) and HYPER + PROP (153 ± 4 mmHg) presented lower SBP compared with HYPER + VEH (P < 0.001). Chronic treatment with losartan, diltiazem, and propranolol reversed cardiac structural microvascular rarefaction (HYPER + VEH 0.16 ± 0.01; EUT + VEH 0.35 ± 0.02; HYPER + LOS 0.46 ± 0.03; HYPER + DILT 0.49 ± 0.02; HYPER + PROP 0.58 ± 0.04 (Vv[cap]/Vv[fib]); P < 0.001) and enhanced the LV ejection fraction of hyperthyroid rats (HYPER + VEH 71 ± 3; EUT + VEH 85 ± 2; HYPER + LOS 90 ± 3; HYPER + DILT 85 ± 3; HYPER + PROP 86 ± 2%; P < 0.05). In conclusion, chronic treatment with losartan, diltiazem, and propranolol improved the cardiac microcirculation and function in an experimental model of hyperthyroidism in rats.