Heterogeneity in conducted arteriolar vasomotor response is agonist dependent

Microiontophoresis of acetylcholine onto cheek pouch arterioles of the pentobarbital-anesthetized hamster results in both a local response at the pipette tip and a conducted dilator response. The conducted response is not dependent on blood flow, and its magnitude decays with distance from the site of stimulation. In an attempt to define the mechanism responsible for activation of arteriolar conduction, vasoactive agonists directed toward different vascular wall cell types, receptor types, and second messengers were applied to arterioles by pressure-pulse microejection. As expected, microapplication caused a consistent arteriolar response at the site of application with each of the agonists tested (local response). However, a high degree of variability was observed among agonists in their ability to produce conducted responses. Acetylcholine, muscarine, and phenylephrine, invariably induced both local and conducted responses. In contrast, bradykinin, substance P, papaverine, isoproterenol, and adenosine, though consistently inducing local responses, displayed a highly variable ability to induce the conducted responses. When conduction was observed, the arteriolar response was similar regardless of the agonist used to induce the response. Microejection of sodium nitroprusside or arginine vasopressin produced local arteriolar responses with no evidence of a conducted response regardless of the dose. These studies reveal previously undetected heterogeneity among microvessel responses and may reflect variations in the coupling mechanisms linking the local vasomotor response to the conducted response.