IMPORTANCE OF VENULAR FLOW IN CONTROL OF ARTERIOLAR DIAMETER IN HAMSTER CREMASTER MUSCLE

These experiments tested the hypothesis that an intact venular flow is important for the control of upstream arteriolar diameter during an increase in metabolism. A silicone stopcock grease dam was placed across the distal portion of the cremaster muscle to localize treatment of the metabolic stimulator 2,4-dinitrophenol (DNP). Thus only the distal area would have an increased metabolic rate, with the proximal area of the cremaster having a normal metabolic rate. During DNP treatment, the first-order venule, approximately 5 mm proximal to the Silastic dam, was occluded to prevent the transport of metabolites. DNP treatment (10 mM) resulted in a significant increase in the arteriolar diameter from 75 +/- 3 to 90 +/- 4 mum (n = 7, P < 0.05), 12.1 +/- 0.3 mm upstream from the distal region. After venular occlusion, arteriolar diameter decreased to 78 +/- 3 mum (P < 0.05). As an additional test of our hypothesis we altered the experimental sequence. DNP treatment during venular occlusion did not affect arteriolar diameter, but after release of the occlusion there was a significant increase in arteriolar diameter from 78 +/- 3 to 91 +/- 4 mum (P < 0.05). These results suggest that an intact venular flow is necessary for control of arteriolar diameter during an increased metabolic rate caused by DNP treatment, providing evidence for the significance of the venular-arteriolar diffusion of vaso-active metabolites.