Hydralazine decreases blood pressure and endothelin-1 mRNA expression in tissues but not cardiac weight in SHR-SP/Izm rats

Although evidence has been accumulated to support a role of endothelin-1 (ET-1) in cardiac hypertrophy, details of the pathophysiological significance of ET-1 in cardiac hypertrophy remain to be elucidated. In the present study, we investigated the effects of the vasodilator hydralazine on the blood pressure, cardiac hypertrophy and ET-1 gene expression in various tissues of spontaneously hypertensive rats (SHR-SP/Izm). Hydralazine (20 mg/kg/day) was administered orally from the age of 4 weeks for 8 weeks. Tissues of the kidney, heart, aorta and brain were obtained at the age of 12 weeks. Tissue expression of ET-1 mRNA was determined by reverse transcriptase polymerase chain reaction (RT-PCR) followed by Southern blot analysis. Administration of hydralazine resulted in a significant decrease in the blood pressure (156 ± 1 mmHg vs 212 ± 4 mmHg in controls) and an increase in the heart rate (470 ± 20 bpm vs 402 ± 23 bpm in controls). ET-1 mRNA expression was significantly decreased in the heart (x 1/2), kidney (x 1/4) and brain (x 1/2). There was no significant change of the cardiac weight (309 ± 4 mg/100 g body weight vs 307 ± 5 mg/100 g body weight in controls). The dissociation between ET-I mRNA expression and cardiac hypertrophy in hydralazine-treated rats may suggest that the increased tissue ET- I is not an indispensable factor of cardiac hypertrophy in hypertension. Sympathetic activation, as shown by the reactive tachycardia, may overcome the effects on the blood pressure and ET-1 expression.