Background: High doses of dihydropyridine calcium channel blockers can activate the sympathetic nervous system and the renin-angiotensin system. Both noradrenaline and angiotensin II stimulate preproendothelin-1 gene expression, yet the effects of high doses of dihydropyridines on preproendothelin-1 expression in vivo remain unknown.
Objectives: To investigate the effects of high doses of dihydropyridines on preproendothelin-1 expression in the ventricles and aorta of normotensive rats.
Methods: Sprague-Dawley rats were treated with amlodipine 5 or 20 mg/kg per day (Amlo 5 or Amlo 20) in drinking water for 5 days or 5 weeks. Systolic blood pressure and heart rate were measured by tail-cuff plethysmography. Gene expression was examined by reverse transcriptase polymerase chain reaction.
Results: Amlo 5 increased heart rate during the first week only and had no effect on blood pressure and ventricular weight and gene expression. Amlo 20 reduced blood pressure transiently and increased heart rate consistently. It did not change relative left ventricular weight (corrected for body weight) after 5 days, but increased it after 5 weeks; it increased relative right ventricular weight at both time points. Aorta weight (mg/mm) was decreased after 5 weeks of treatment with both dosages of amlodipine. Preproendothelin-1 mRNA levels were increased by Amlo 20 in the ventricles and aorta and, concomitantly, renin mRNA was increased in the kidney. Less consistently, interleukin-6 mRNA also increased in ventricles, whereas cardiotrophin-1 mRNA remained unchanged. The sensitivity of isolated aorta to the contractile effect of noradrenaline was decreased by Amlo 5, but not by Amlo 20.
Conclusions: In Sprague-Dawley rats, high-dose amlodipine, while promoting neurohormonal activation, induced overexpression of preproendothelin-1 mRNA in the ventricles and aorta. Endothelin-1 overexpression could contribute to the lack of inhibitory effect of high-dose amlodipine on ventricular mass in normotensive rats.