Comparative Cardiovascular Effects of the Angiotensin II Type 1 Receptor Antagonists ZD 7155 and Losartan in the Rat

Binding experiments show that ZD 7155 is a potent angiotensin II type 1 receptor antagonist. In this study this novel substance was studied in normotensive and hypertensive rats. The relative potency and duration of the antihypertensive effects of ZD 7155 were compared with those of the reference substance, losartan. The inhibitory effects of both compounds on angiotensin II-induced pressor actions were studied in the conscious normotensive Sprague-Dawley (SD) rat and in the conscious, spontaneously hypertensive rat (SHR). Arterial blood pressure and heart rate (HR) were obtained by direct intraarterial recording. Angiotensin II infusion was administered intravenously in the dose range 53.3 ng-12.8 micrograms kg-1 min-1 to the conscious rats. ZD 7155 was administered in a bolus dose of 1.082 mumol kg-1 (0.51 mg kg-1) and losartan in bolus doses of 2.165 and 6.495 mumol kg-1 (1.0 and 3.0 mg kg-1). In conscious SD rats, ZD 7155 and losartan behaved as competitive antagonists and the pressor response curve to angiotensin II was shifted to the right. Experiments in conscious SD rats also showed that ZD 7155 was approximately ten times as potent as losartan in suppressing the angiotensin II-induced pressor response (240 ng kg-1; 10 min infusion). In addition, experiments with conscious rats demonstrated that ZD 7155 could suppress the angiotensin II-induced pressor response for approximately 24 h when ZD 7155 was administered intravenously in a 1.082 mumol kg-1 bolus dose and angiotensin II was given at 240 ng kg-1 (in a 10-min infusion). Experiments in conscious SHRs using ZD 7155 (1.082 mumol kg-1) and losartan (6.495 mumol kg-1) as intravenous boluses indicated that both ZD 7155 and the reference compound losartan exhibited a significant antihypertensive effect. These results demonstrate that ZD 7155 is a potent angiotensin II-type 1 antagonist which is approximately ten times as potent as losartan in suppressing the angiotensin II-induced pressor response. Furthermore, ZD 7155 may suppress the angiotensin II-induced pressor response for 24 h and in the SHR ZD 7155 induces a pronounced and persistent antihypertensive effect.