[The role of circular and tangential smooth-muscle fibers in arteriole constriction and closure].

Equations reflecting relationships between the thickness of blood vessel wall (w) and internal radius (r) of the vessel during the process of smooth muscle fiber contraction involved two types of the fibers orientation in vessel wall: at an angle of 45 degrees and 90 degrees to the longitudinal axis of the vessel. Experimental values of w and r were determined on arterioles of the rat mesentery after vasopressin or epinephrine administration. According to the degree of longitudinal and transversal efforts participation in the process of vessel closure, heterogeneity of the arterioles was revealed by comparison of the theoretical and experimental values of w and r. The ability of arterioles for closure did not depend on the initial value of relative vessel wall thickness (w/r).