Cross-over study comparing effects of treatment with an angiotensin converting enzyme inhibitor and an angiotensin II type 1 receptor antagonist on cardiovascular changes in hypertension.

OBJECTIVE: To compare the blood-pressure-lowering effects of an angiotensin converting enzyme inhibitor, perindopril, with those of an angiotensin II type 1 receptor antagonist, L-158,809, for adult spontaneously hypertensive rats.
DESIGN: A cross-over design was used, to treat adult spontaneously hypertensive rats with one drug for 10 weeks, and then with the other for 5 weeks.
METHODS: Adult, male spontaneously hypertensive rats (aged 15 weeks) were treated daily by gavage for 10 weeks with perindopril (P group) or L-158,809 (L group), then treatment was crossed over so that rats in the P group were treated with L-158,809 (P/L group) and rats in the L group were treated with perindopril (L/P group) for 5 weeks. Blood pressure was measured weekly. Plasma angiotensin converting enzyme activity, renal angiotensin receptor density, and arterial structure and functioning were measured after the single and crossover treatment periods.
RESULTS: Treatment lowered the blood pressure from 206 +/- 2 mmHg in rats in the control group, to 126 +/- 2 in rats in the P group and 150 +/- 2 in rats in the L group. After the cross-over period, blood pressure decreased further from 150 +/- 2 to 129 +/- 3 mmHg in rats in the L/P group, whereas blood pressure of spontaneously hypertensive rats in the P/L group increased from 126 +/- 2 to 148 +/- 2 mmHg. Perindopril treatment almost abolished plasma angiotensin converting enzyme activity, whereas L-158,809 treatment had no effect. Renal angiotensin II receptor density was decreased versus baseline in rats in the P and L groups. The affinity of binding was decreased versus baseline in rats in the L group. A positive correlation to blood pressure was found for mesenteric artery wall thickness and wall: lumen ratio. Concentration for half-maximal effect for the response of mesenteric arteries from rats in the P group to norepinephrine was lower than that of the control group rats. Angiotensin II potentiated the norepinephrine-stimulated contraction of arteries from rats in the control and P groups, but not that of arteries from rats in the groups treated with L-158,809.
CONCLUSION: Perindopril was more effective than was L-158,809 at lowering the blood pressure of adult spontaneously hypertensive rats, and at altering the structure and functioning of the arteries.