Effects of the Antihypertensive Dilevalol on Aortic Compliance in Anesthetized Dogs

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Abstract
The present study examined the actions of dilevalol, an antihypertensive β-adrenoceptor blocker with arterial vasodilator actions, on aortic compliance (AC) in anesthetized dogs. AC was measured by sonomicrometric determination of the ratio of aortic systolic-diastolic diameters (mm) and arterial pulse pressure (mm Hg). One AC unit (ACU) equals 10−3 mm/mm Hg. Dilevalol (0.032, 0.1, and 3.2 mg/kg intravenously, i.v.) significantly (p < .05) increased AC by 1.4 ± 0.3, 3.7 ± 1.4, and 4.5 ± 1.2 ACU from basal values of 4.7 ± 0.4–5.6 ± 0.4 ACU while reducing blood pressure by 20 ± 2, 31 ± 9, and 41 ± 10 mm Hg, respectively (p < 0.05). Increases in AC were not the passive result of altered blood pressure. Proximal mechanical aortic occlusion dropped systolic blood pressure as much as 70 mm Hg without altering AC. Hydralazine also (0.3 and 1.0 mg/kg i.v.) lowered blood pressure significantly (p < 0.05) by 14 ± 3 and 40 ± 4 mm Hg but increased AC only at 1.0 mg/kg (+ 1.6 ± 0.4 ACU, p < 0.05). Phenylephrine (1–30 μg/kg i.v.) significantly raised blood pressure 25 ± 3–95 ± 8 mm Hg but decreased AC significantly by 1.2 ± 0.3–2.4 ± 0.3 ACU. Isoproterenol (ISO) (0.01–1.0 μg/kg) produced effects on AC similar to those of dilevalol. Propranolol pretreatment attenuated dilevalol and ISO-induced increases in AC. Propranolol (0.32 and 1.0 mg/kg) did not significantly change AC. Pindolol (0.1–1.0 mg/kg i.v.) lowered blood pressure 17 ± 3 (p < 0.05) to 34 ± 7 mm Hg (p < 0.05) while significantly increasing AC by 1.2 ± 2–2.7 ± .7 ACU. Nitroglycerin was the most effective agent studied: At 0.1–10 μg/kg i.v., it increased AC by 0.3 ± .1–7.9 ± 2.0 ACU. The data show that dilevalol, unlike propranolol, increases AC substantially at antihypertensive doses. The inhibition of dilevalol-induced AC increases by propranolol demonstrates a β-adrenoceptor agonist activity in large arteries.