Abstract
The aim of this study was to evaluate the effectiveness of an angiotensin-converting enzyne inhibitor (ACEI, quinapril) or angiotensin II receptor blocker (ARB, candesartan) on atrial natriuretic peptide (ANP) activity in rats with hypertension induced by nitric oxide (NO) inhibition. ACEI and ARB have a number of pharmacologic effects, including blood pressure reduction, myocardial preservation, and an unknown effect in the circulation. The changes in ANP in NO inhibitor-induced hypertensive rats were evaluated in order to elucidate the interaction between ANP and NO in the regulation of blood pressure. Thirty-six rats were divided into 4 groups and administered the experimental agents for 8 weeks: group Control was given regular food (n=9), group NG-nitro-L-arginine (L-NNA) was administered L-NNA (25 mg · kg-1 · day-1, n=9), group ACEI was administered L-NNA and quinapril (10 mg · kg-1 · day-1, n=9), and group ARB was administered L-NNA and candesartan (10 mg · kg-1 · day-1, n=9). Blood pressure, plasma ANP, atrial ANP, ANP mRNA, and ANP granules were measured. A significant elevation in blood pressure was observed in group L-NNA. However, there were no increases in plasma ANP (L-NNA: 138.8±64.4, Control: 86.7±36.4), ANP mRNA (L-NNA: 2.2±1.0, Control: 1.7±0.5) or ANP granules (L-NNA: 61.1±10.2, Control: 64.5±8.5). No increase in blood pressure was seen in groups ACEI and ARB. However, plasma ANP (ACEI: 1,392.3±1,034.4, ARB: 1,142.8±667.3), ANP mRNA (ACEI: 52.8±29.1, ARB: 42.9±21.2), and ANP granules (ACEI: 122.5±23.4, ARB: 136.3±33.2) increased significantly. NO inhibitor-induced hypertension caused no changes in ANP concentrations. However, the ACEI and ARB had a direct effect on the induction of ANP secretion. The findings suggest that ANP secretion is directly effected by ACEI and ARB, which seems to play a key role in lowering blood pressure, relieving heart failure symptoms, and preserving the myocardium. (Circ J 2003; 67: 1053 - 1058)
