Losartan is more effective than angiotensin (1-7) in preventing thyroxine-induced renal injury in the rat

Studies have shown that renal hypertrophy seen in experimental hyperthyroidism induced by thyroxine (T4) is due to angiotensin (Ang) II. However, other renal effects of Ang II in experimental hyperthyroidism have not been investigated. In addition, Ang 1-7 is believed to be protective against renal injury, but its possible role in thyroxine-induced renal injury is not known. The aim of this study is to elaborate the role of Ang II in thyroxine-induced renal injury and the possible protective role of Ang 1-7. We hypothesize that Ang 1-7 will be as protective against thyroxine-induced renal injury as the use of an ACE inhibitor or an Ang II receptor blocker. Adult Sprague Dawley rats were used in this study and were divided into 5 groups: (1) Control (treated with vehicle), (2) Treated with thyroxine (T4, 100 µg/kg), (3) Treated with T4 and Ang 1-7 (500 µg/kg), (4) Treated with T4 and captopril (20 mg/kg), and (5) Treated with T4 and losartan (10 mg/kg). Parameters tested after fourteen days of treatment were creatinine clearance, protein excretion rate, glomerular volume, renal ACE1 and ACE2 protein expression. Data were compared using One-way-ANOVA followed by Tukey's HSD post hoc test. Thyroxine caused glomerular hypertrophy and proteinuria but had no effect on glomerular filtration rate (GFR). Glomerular hypertrophy was prevented by losartan and captopril, but not by Ang 1-7. Captopril and losartan had no effect on GFR; however, Ang 1-7 caused an increase in GFR in T4-treated rats. The increase in protein excretion rate was prevented by losartan but not by captopril or Ang 1-7. Renal expression of ACE1 protein was not altered in any of the treatment groups except in captopril treated rats were ACE1 expression was increased. Renal ACE2 protein expression was only increased in T4-losartan-treated rats and not affected by any of the other treatments. We conclude that losartan was more protective than captopril against thyroxine-induced renal changes while Ang 1-7 offered no protection.