Effects of ofx-Blockade on Arterial Compliance in Normotensive and Hypertensive Rats

The effects of blockade of cq-adrenergic receptors on the mechanical properties of the arterial wall were studied in 10 spontaneously hypertensive rats (SHR) as compared with 10 matched normotensive Wistar-Kyoto (WKY) rats. Ascending aortic pressure and flow were recorded in open-chest anesthetized rats, and the systemic arterial compliance was calculated. Intravenous injection (1 mg/kg) of Urapidil, a selective «,-adrenergic antagonist, induced a significant decrease in arterial pressure (-26%, p<0.01 and -37%, p<0.001 in WKY rats and SHR, respectively) without significant changes in cardiac output. In control conditions, systemic arterial compliance was lower in SHR (3.29 ±1.52 /il/mm Hg) than in WKY rats ( 4 J 5 ± U 5 fil/mm Hg, p<0.01). Urapidil injection induced significant increases in systemic arterial compliance values in both strains (p<0.001). In another set of experiments (15 WKY rats and 15 SHR), the carotid compliance (filjmm Hg) was determined from the arterial volumepressure relation under control conditions, after local incubation with Urapidil, and after total abolition of the vascular smooth muscle by KCN. In WKY rats, the carotid compliance increased markedly after incubation with Urapidil at doses corresponding to 1 mg/kg (+31%, p<0.01). A further increase in the carotid compliance was observed after KCN poisoning (+11%, p<0.05). In SHR, incubation with Urapidil at doses corresponding to 2 mg/kg were necessary to induce a significant increase in compliance (+38%). At this dosage, there was no further increase in compliance after KCN poisoning. The present study suggests that (^blockade influences the arterial compliance in normotensive and hypertensive rats independently of its effects on the arterial blood pressure. (Hypertension 1991;17:534-540)