Chronic antihypertensive treatment with captopril plus hydrochlorothiazide improves aortic distensibility in the spontaneously hypertensive rat.

1. Adult male spontaneously hypertensive rats (SHR) were given captopril plus hydrochlorothiazide mixed in the diet for 10 weeks. Calculated daily doses were 44 mg kg-1 per day for captopril, and 22 mg kg-1 per day for hydrochlorothiazide. Separate groups received captopril or hydrochlorothiazide alone, at similar doses, or no treatment. A final group of WKY normotensive rats received no drug. 2. Systolic arterial blood pressure, measured at regular intervals throughout the 10 weeks' period was lowered but not normalized, in groups receiving either captopril plus hydrochlorothiazide, or captopril alone, but not in the group receiving hydrochlorothiazide alone. 3. Following pentobarbitone anaesthesia, systolic arterial blood pressure, measured in the femoral artery, was found to be lower in all treated groups, but the greatest effect was observed in SHR previously treated with captopril plus hydrochlorothiazide. Aortic pulse wave velocity was also lower in treated SHR, and once again the greatest decrease was observed in the group previously treated with captopril plus hydrochlorothiazide. 4. Following pithing, systolic arterial blood pressures were similar in all SHR groups. Aortic pulse wave velocity was lower in pithed rats previously treated with captopril and hydrochlorothiazide. 5. In conclusion, antihypertensive treatment of SHR produces falls in blood pressure and pulse wave velocity, an indicator of aortic distensibility. Results in pithed rats suggest that treatment with the combination of captopril plus hydrochlorothiazide may increase aortic distensibility independently of blood pressure.