Effects of angiotensin II receptor antagonist and angiotensin converting enzyme inhibitor on blood pressure and angiotesin II contents in plasma and renal tissue of renovascular hypertensive rats

Objective To study the therapeutic effects and characteristics of ACEI and AngⅡ receptor antagonist.Methods The 2K1C hypertensive rat model was made.Vascular ring was isolated to assess the AngⅡ-induced vasoconstriction.Blood pressure was measured through carotid canula and tail-cuff manometer.The plasma and renal tissue AngⅡ contents were determined using radioimmunoassay kit.Results ①Isolated vascular ring study:AngⅡinduced a dose-dependent vasoconstriction response.Losartan(1×10~(-6) mol/L) could completely block the AngⅡ-induced vasoconstriction,while captopril(1×10~(-6) mol/L) did not show effects on AngⅡ-induced vasoconstriction except a slight inhibitory action at small doses of AngⅡ.②Acute depressor effects:captopril of 0.1 mg/kg(the maximal effective dosage) decreased the mean blood pressure(MAP) from control value of(18.4±3.9) kPa to(8.7±1.2) kPa(decrease by 9.6 kPa),whereas losartan 2 mg/kg(the maximal effective dosage) decreased the MAP from(16.8±1.1) kPa(contol) to(11.4±2.4) kPa(decrease by 5.30 kPa).Following the first administration of captopril,reapplication of losartan could not further decrease the MAP;However,after the first administration of losartan,reapplication of captopril could still further decrease the MAP by 2.12 kPa(P0.05).③Chronic depressor effects:after gavage administration of the agent for four weeks,captopril and losartan decreased the MAP from(18.9±2.5) kPa to(11.8±1.6) kPa and from(19.7±2.4) kPa to(11.7±2.0) kPa respectively,with no significant differences between two groups.Radioimmunoassay:after the four-week gavage administration,the plasma AngⅡ content was(376±72) ng/L,which was significantly lower than control value(526±78) ng/L in captopril group,and the plasma AngⅡ content was(1 036±159) ng/L in losartan group which was significantly higher than control value.The renal tissue AngⅡ content was(392±81) pg/g in captopril group and(294±86) pg/g in losartan group,both were significantly lower than control value(431±80) pg/g.Conclusion The acute depressor effects of captopril are larger than that of losartan,while the chronic depressor effects are no significant differences between the two agents,indicating that the plasma AngⅡ contents are unrelated to the maintenance of hypertension,while the renal tissue AngⅡ contents are responsible for the chronic hypertension.