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