Microvascular permeability to endogenous plasma proteins in the jejunum.

Steady-state lymph flow and lymph (CL) and plasma (CP) protein concentrations were measured at venous outflow pressures of 0, 10, 20, and 30 mmHg in an autoperfused segment of cat jejunum. In addition to determining total protein concentrations in lymph and plasma, polyacrylamide gradient gel electrophoresis was used to determine lymph and plasma protein concentrations of albumin and nine other plasma proteins. The osmotic reflection coefficient (sigma d) for total proteins, albumin, and each of the nine protein fractions was estimated using CL/CP at a capillary filtration rate independent state, when 1 - CL/CP = sigma d. A sigma d of 0.83 was obtained for total proteins, a value similar to that reported for both dog jejunum and descending colon (0.85) but appreciably different from that reported for both cat stomach (0.78) and ileum (0.92). Additionally, sigma d for albumin and each of the nine plasma protein fractions (molecular radii ranging from 37 to 120 A) increased as molecular radius increased. A two-pore model composed of a ratio of 3,750 48-A radius small pores to one 250-A radius large pore describes the data obtained, with 82% of the total volume flow occurring through the small pores and 16% through the large pores.