Antihypertensive action of amiodarone in spontaneously hypertensive rats

The antihypertensive effect of amiodarone was investigated in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The SHR and WKY were treated with amiodarone (1 mg/mL PO) or tap water (control) fo r 20 weeks. The indirect arterial pressure (AP) was monitored weekly using the tail-cuff method. At the end of the 20th week, the direct AP was measur ed, and the systolic AP and pulse interval time series were submitted to au toregressive spectral analysis. In addition, cardiac baroreflex sensitivity and left ventricular weight were evaluated as well. The indirect AP was re duced 1 week after the beginning of amiodarone treatment. The direct mean A P and pulse interval were, respectively, 135 +/-8 mm Hg and 191 +/-3 ms in SHR treated with amiodarone (187 +/-8 mm Hg and 156 +/-7 ms in control SHR, P <0.05) and 87 +/-3 mm Hg and 207 +/-8 ms in WKY treated with amiodarone (105 +/-8 mm Hg and 174 +/-4 ms in control WKY, P <0.05). In SHR treated wi th amiodarone, the low-frequency oscillations of AP were lower (8.5 +/-1.2 mmHg(2) versus 14.4 +/-2.9 mmHg(2) in control SHR, P <0.05), whereas the re flex bradycardia was higher (0.84 +/-0.12 ms/mm Hg versus 0.32 +/-0.22 ms/m m Hg in control SHR, P <0.05). The left ventricle weight was also smaller i n SHR treated with amiodarone (2.94 +/-0.12 mg/g versus 3.45 +/-0.24 mg/g i n control SHR, P <0.05). In WKY, amiodarone induced similar changes as in S HR, except for a lack of effect in the left ventricle weight. These data in dicate that amiodarone has an antihypertensive action in SHR that is associ ated with a reduction in vasomotor sympathetic modulation, an increase in v agal cardiac baroreflex sensitivity, and a decrease in cardiac hypertrophy.