Effects of biaxial stretch on arteriolar function in vitro

Mounting evidence suggests that the normal biomechanical state of arteries may include a nearly equibiaxial intramural stress, and that arteries tend to undergo rapid and dramatic remodeling when perturbed from this normal state. Technical developments in the early 1980s and late 1990s enabled in vitro and ex vivo studies, respectively, of isolated perfused microvessels, and it is clear that they share many similarities in behavior with arteries. To date, however, there has been no systematic study of the effects of biaxial loading on the biomechanical behavior of arterioles. In this project, we describe a modification to a prior in vitro arteriole test system that allowed us to investigate the role of altered axial stretch on the passive, myogenic, and fully contracted biaxial behavior of isolated rat cremaster arterioles. We show that axial stretches from 85% to 110% of normal values induce modest changes in the measured circumferential and axial stress-stretch behavior and similarly in traditional measures of distensibility and myogenic index. Nevertheless, altered axial stretch has a dramatic affect on the biaxial state of stress and it appears that near equibiaxial stress occur at axial stretches larger than those used previously. Whereas this finding will not affect prior estimates of material and functional behavior, it may have important implications for the design of long-term ex vivo and in vivo studies wherein vessel growth and remodeling are critical.