Control of the arteriolar myogenic response by transvascular fluid filtration

Mechanisms of the myogenic response have not been completely established. We hypothesized that transvascular fluid filtration from plasma across smooth muscle cells (SMC) and into the surrounding interstitium helps regulate arteriolar myogenic tone. Arteriolar diameters in the rat mesentery were monitored before and following vascular occlusion with a glass micropipette. Arteriolar occlusion not only gave an increase in hydrostatic pressure that initiated myogenic constriction upstream of the pipette, but also allowed measurement of fluid filtration rate by monitoring the movement of vascular red blood cells. A statistically significant correlation (P < 0.001) existed between basal myogenic tone and fluid filtration. Additionally, the myogenic response was attenuated by 47% +/- 7% (N = 10) when an osmotic solution of albumin or albumin plus Ficoll was infused into the bloodstream to decrease fluid filtration by 53% +/- 3%. Moreover, the same inhibition of myogenic tone was found in isolated, cannulated rat soleus muscle arterioles when filtration was osmotically attenuated by intravascular dextran. Taken together, these results are consistent with the hypothesis that shear stress on arteriolar smooth muscle, induced by transvascular fluid filtration, is a contributing factor that helps control myogenic tone. (C) 2004 Elsevier Inc. All rights reserved.