ATTENUATION OF BLOOD FLOW-INDUCED DILATION IN ARTERIOLES AFTER MUSCLE-CONTRACTION

The response of third-order arterioles (n = 15) in rat-cremaster muscl e to increased luminal flow was studied after brief (20-30 s) occlusio n of a neighboring arteriole in pentobarbital-anesthetized rats. Red c ell velocity increased almost fivefold (485 +/- 54% of control) during occlusion, and vessel diameter increased 63 +/- 11%. Initially, the c alculated wall shear rate increased to 430 +/- 40% of control during o cclusion but then decreased to 308 +/- 35% of control as a consequence of arteriolar dilation. The muscle was subsequently stimulated to con tract for 1 min, and the occlusion procedure was repeated after arteri olar diameter and red cell velocity had returned to control levels. In this instance the vessel dilation was 34 +/- 10% or about one-half of that seen during the previous occlusion, although velocity and shear rate rose to a similar degree (474 +/- 54 and 397 +/- 35%, respectivel y). Dilation during a third occlusion 2-7 min after the vessel recover ed from the second occlusion was as great as during the first occlusio n (77 +/- 20%). The results indicate that flow-induced dilation in art erioles of rat cremaster muscle is transiently attenuated after muscle contraction.