Ang II receptor expression and effect of Ang II receptor blockade in thyrotoxic rat myocardium

To investigate the relationship between expression of the angiotensin II (Ang II) receptors and thyroid hormones in the myocardium of rats with thyrotoxicosis.

Forty-four adult male Sprague-Dawley rats were divided into four groups: control group (saline), losartan group (10 mg/kg), thyrotoxicosis group (0.5 mg/kg L-thyroid hormone sodium) and thyrotoxicosis-plus-losartan group (0.5 mg/kg L-thyroid hormone plus 10 mg/kg losartan) and treated intragastrically daily for four weeks. The heart weight (HW), body weight (BW) and HW/BW ratios were determined. The Ang II protein contents in cardiac homogenates and serum were determined by ELISA. The serum concentrations of levothyroxine (T3), trilodothyronine (T4) and thyroid stimulating hormone (TSH) were measured by radioimmunoassay. The expression of angiotensin II type 1 receptor (AT1R) and angiotensin II type 2 receptor (AT2R) were quantified by real-time PCR and Western blotting.

The thyrotoxicosis group had an increased BW/HW and higher cardiac AT1R and AT2R expression compared to controls. AT1R and AT2R expressions significantly reduced in the thyrotoxicosis-plus-losartan group, compared to the thyrotoxicosis group.

Thyroid hormone upregulated cardiac AT1R and AT2R, leading to cardiac remodeling, which was reversed by losartan. Cardiac damage in thyrotoxic rats may be related to upregulation of the Ang II receptors.