MECHANICAL CHARACTERISTICS AND ACTIVE TENSION GENERATION IN RAT INTESTINAL ARTERIOLES

The contributions of active and passive wall tension to regulation of arteriolar diameters were determined for large (1A), intermediate (2A), and small (3A) arterioles in the small intestine of the anesthetized rat. Active tension (T(a)) contributed > 85% of total wall force at rest in 2A and 3A and 75-80% of total force in 1A. T(a) was approximately 90% of peak active tension (T(a,peak)) for large through small arterioles, even though absolute T(a) varied by fourfold. A linear relationship between microvascular pressure and T(a) was observed for decreases in pressure in all arterioles. T(a) remained nearly constant for pressure increases of 40% in 2A and 3A but was increased in 1A. Because of the plateau of the circumference-T(a) relationship near T(a,peak), superfusion of progressively increasing concentrations of norepinephrine or adenosine resulted in maintenance of the close T(a)-T(a,peak) relationship unless the vessel diameter changed > 25%. These results indicate that, while arteriolar diameters vary substantially, near-peak T(a) is generated for a variety of physiological conditions.