Component analysis of change in fluid shear stress (Δτ) stimulus and basal capillary hydraulic conductivity (Lp)

Abstract

One δτ stimulus consists of two components: flow increase and flow plateau. Previously, we reported lower Lp following acute, ramp versus square wave δτ, consistent with rate sensing capability (Microvasc Res 66:2003). Here, basal capillary Lp following δτ was evaluated in terms of rate and magnitude of change. We hypothesized that rate and magnitude of δτ would correlate with Lp. Frogs (Rana pipiens, N=26) were pithed and the mesentery was exteriorized and superfused with frog Ringer's (14‐16°C). Either one or two true capillaries/frog were cannulated at 10 cm H2O and perfused with 10 mg.ml−1 BSA dissolved in Ringer's. After 2 min of low flow each capillary was stimulated with ramp δτ (steady infusion pump) and a plateau was established (2 min). Lp was assessed at 30 cm H2O using the modified Landis technique. Range for acceleration (a) was 27.1 to 202.6 μm▸s−2 and 9.5 to 82.6 dynes▸cm−2 for δτ. Mean±SE Lp was 3.1±0.2 x 10−7 cm.s−1.cm H2O−1 (n=31). Lp correlated negatively with a (slope=‐0.020; R2=0.45; P=0.0002) and positively with magnitude of δτ (slope=0.048, R2=0.37, P=0.0003). δτ /a strengthened the relationship (slope=2.95, R2=0.63, and P<0.0001). These data are consistent with a transducer/signaling mechanism in the capillary wall that senses both components of δτ, integrates them, and adjusts Lp accordingly. Both rate and magnitude of change in blood flow likely impact tissue hydration. Supported by RO1 HL63125