Assessment of in vivo Aortic Wall Characteristics at the Early Stage of Atherosclerosis in Rabbits

To assess wheter vascular responsiveness to α-receptor agonist is altered or not at the early stage of atherosclerosis, in vivo aortic pressere-diameter relationship of aorta over a wide range of pressere was analyzed before and after the acute administration of α-receptor agonist (phenylephine) in 9 hyper cholesterolemic fat-fed (7 weeks) rabbits and 8 normal diet-fed (7 weeks ) rabbits. There was no significant difference in the aortic wall thickness between both groups, suggesting the early stage of atherosclerosis. Using a modified three element Max well model, diastolic stress-strain relationship was computed after applying several assumptions to the astual aortic pressure-diameter relationship. After the intravenous administration of phenylephrine at a rate of 5 mg/ kg/ min, the atress (ordinate)-atrain (abscissa) relation curves were shifted to the left, indicating the activation of aortic smooth muscle by phenylephrine. The difference in the stress before and after phenylephrine infusion showed a single peak at a certain strain. The peak difference in the stress was smaller in hypercholesterolemic fat-fed rabbits than in normal diet-fed rabbits, indicating the decreased vascular responsiveness at the early stage of atherosclerosis.

Hypercholesterolemia

Aortic smooth mscle

Atherosclerosis

Stess-strain relationship

Phenylephrine