A test of the role of flow dependent dilation in arteriolar responses to occlusion. McGahren, Eugene D., Kim A. Dora, David N. Damon, and Brian R. Duling. Departments of Molecular Physiology and Biological Physics, and Surgery, University of Virginia Health Sciences Center, Charlottesville, Virginia 22908
APStracts 3:0320H, 1996.
At an arteriolar bifurcation, occlusion of one of the branch arterioles has been reported to result in an increase in flow, shear stress, and vasodilation in the opposite unoccluded branch. This dilator response in the unoccluded branch, often referred to as the "parallel occlusion response", has been cited as evidence that flow dependent dilation is a primary regulator of arteriolar diameter in the microcirculation. It has not been previously noted that during this maneuver, flow through the feed arteriole would be expected to decrease, and logically should causecausing that vessel to constrict. We tested this prediction in vivo by measuring red blood cell (RBC) velocity and diameter changes in response to arteriolar occlusion in the microcirculatory beds of three preparations, the hamster cheek pouch, hamster cremaster, and the rat cremaster. In all preparations, a vasodilation was observed in the feed arteriole, despite a decrease in both flow and calculated wall shear stress through this vessel. Unexpectedly, we found that dilation occurred in the unoccluded branch arterioles even in those cases where RBC velocity and shear stress did not increase in the unoccluded branch arterioles. All values returned to baseline after removal of occlusion. The magnitude of the dilation of the feed and branch arterioles varied between species and tissues, but feed and branch arterioles within a given preparation always responded in a similar way to each other. We conclude from our experiments that mechanisms other than flow dependent dilation are involved in the vasodilation observed in the microcirculation during occlusion of an arteriolar branch. 

Received 4 August 1995; accepted in final form 22 July 1996.
APS Manuscript Number H736-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996