Propagation of vasomotor responses coordinates arteriolar resistances

We tested the hypothesis that a conduction pathway intrinsic to the arteriolar wall possesses the properties necessary to coordinate vasomotor responses in the microcirculation. Acetylcholine (ACh) or norepinephrine (NE) was iontophoresed onto cheek pouch arterioles (15-35 microns diam) of pentobarbital-anesthetized hamsters, and diameter responses were observed using intravital video microscopy. ACh and NE induced vasodilation and vasoconstriction, respectively, that propagated both upstream and downstream from the site of application. Propagated vasomotor responses decayed with distance along the arterioles; this decay was characterized by mechanical length constants of 1.9 and 1.8 mm for ACh and NE, respectively. Vasodilations and vasoconstrictions initiated on daughter vessels of a branch propagated into parent arterioles that were approximately twice the diameter of the daughter vessels. Iontophoretic stimuli applied simultaneously to paired daughter vessels induced propagated responses that summed linearly in the parent vessel. We conclude that the arteriolar network functions as a highly coordinated syncytium and that diverse vasomotor stimuli can be summed and integrated within the peripheral microvasculature.