Ramp acceleration and hydraulic conductivity (L(p)) of living capillaries.

Living mesenteric capillaries with either an intact or disrupted glycocalyx were challenged with ramp change in shear stress (Deltatau). Animals (Rana pipiens) were divided randomly into two experimental groups, and two true capillaries (TC) per animal were investigated. The modified Landis technique was combined with intravital microscopy to view individual TC and assess hydraulic conductivity (L(p)), an index of capillary function. Median L(p) was 3.2 x 10(-7) for control and 11.8 x 10(-7) cm s(-1) cm H(2)O(-1) after mild, brief (1 min) pronase treatment (P<0.0001). Analysis by stimulus component showed that L(p) for untreated capillaries was related negatively to ramp acceleration (R(2)=0.46, P<0.0001, n=38) and positively to Deltatau magnitude (R(2)=0.28, P=0.0006, n=38). Disrupting the capillary glycocalyx revealed a positive and previously unknown relationship between ramp acceleration and L(p) (R(2)=0.44, P=0.002, n=19) plus an upward shift (increased intercept) of the magnitude Deltatau-L(p) relationship compared to abrupt stimulation. These data suggest that bloodstream hemodynamics may impact capillary function. Further, an intact glycocalyx may protect capillaries when blood flow changes. Copyright 2009 Elsevier Inc. All rights reserved.