AJP - Gastrointestinal and Liver Physiology, Vol 239, Issue 4 300-G305, Copyright © 1980 by American Physiological Society
Permeability characteristics of colonic capillaries
P. D. Richardson, D. N. Granger, D. Mailman and P. R. Kvietys
Blood flow, lymph flow, lymph protein concentration (CL), lymph oncotic
pressure, plasma protein concentration (CP), and plasma oncotic pressure
were determined under steady-state conditions at venous pressures of 0, 10,
20, 30, and 40 mmHg in autoperfused segments of dog colon. Venous pressure
elevation increased colonic vascular resistance, lymph flow, lymphatic
protein flux, and the transcapillary oncotic pressure gradient, whereas the
lymph-to-plasma protein concentration ratio (CL/CP) declined. The osmotic
reflection coefficient (sigma d) was estimated using sigma d = 1-CL/CP when
CL/CP is filtration independent (high lymph flows). For total protein sigma
d = 0.85 +/- 0.02. Values of sigma d for plasma protein fractions with
molecular radii ranging between 37 and 120 A increased as molecular radius
increased. The results of this study suggest that 1) colonic capillaries
selectively restrict macromolecules on the basis of molecular size, and 2)
an increased lymph flow and transcapillary oncotic pressure gradient may
play an important role in preventing interstitial edema subsequent to
venous pressure elevation in the dog colon.
