title: A shear stress component to the modulation of capillary hydraulic conductivity (Lp).
abstract: OBJECTIVE
  Two major factors that determine transcapillary exchange are Starling forces and hydraulic conductivity (Lp) of capillary walls. Although chemical stimuli alter Lp, the influence of mechanical stimuli has been neglected. Therefore, we tested the hypothesis that the Lp of intact capillaries would increase with the magnitude of changes in shear stress presented to each capillary.
  
  
  METHODS
  Capillaries (n = 26) in the mesentery of pithed frogs (n = 23) were cannulated at 30 cm H2O (average in situ pressure = 9.2) to alter shear stress. For the calculation of shear stress, velocities of both frog red blood cells (RBC) and human RBC in the pipette solution were measured in each capillary before and after cannulation, respectively. Lp was assessed 2 min after cannulation.
  
  
  RESULTS
  Venular capillaries only responded to the changes in shear stress. The magnitude of the changes in shear stress correlated positively with the values for capillary Lp (Kendall's tau = 0.56; p = 0.02).
  
  
  CONCLUSIONS
  While Starling forces influence the movement of fluid by acting perpendicular to the long axis of capillaries, shear stress acts in a plane tangential to the capillary walls and appears to alter capillary Lp. In addition to chemical stimuli, the mechanical stimulation of capillaries can alter the barrier itself and consequently alter filtration rate.
authors.affiliation: Department of Physiology, University of Missouri-Columbia 65212, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Williams
mesh_terms: D000818:Animals; D001160:Arterioles / Q000502:physiology; D001783:Blood Flow Velocity; D002199:Capillary Permeability / Q000502:physiology*; D004912:Erythrocytes; D018056:Hemorheology; D006801:Humans; D007552:Isotonic Solutions / Q000493:pharmacokinetics; D008643:Mesentery / Q000098:blood supply; D011894:Rana pipiens; D000077331:Ringer's Solution; D012710:Serum Albumin, Bovine / Q000493:pharmacokinetics; D013314:Stress, Mechanical; D014699:Venules / Q000502:physiology
chemical_list: D007552:Isotonic Solutions; D012710:Serum Albumin, Bovine; D000077331:Ringer's Solution