Shaking of the intact rat and intestinal angulation diminish the jejunal unstirred layer

A sizeable pre-epithelial diffusion barrier (unstirred layer) is present during perfusion of the rat jejunum. In the present study, three rapidly transported compounds, CO, [¹⁴C]warfarin, and glucose (5.5 mmol/L), were used as probes to assess the ability of manipulations to reduce the unstirred layer. This layer was 700-800 μm thick in a 30-cm jejunal segment perfused in conventional fashion on the abdominal wall. Placement of four sharp angulations in the segment or replacement in the abdominal cavity reduced the maximal unstirred layer to 200-400 μm. Increasingly rapid shaking of the anesthetized, intact rat on a platform shaker produced progressively thinner unstirred layers. At 250 revolutions per minute, the maximal layer ranged from 32 to 68 μm for the three probes and may have been appreciably less if the epithelium offered appreciable resistance. Shaking yields a > 15-fold reduction in unstirred layer resistance and provides a means for measuring this resistance and for obtaining more accurate assessment of the true in vivo transport Michaelis constant (K_m) of any compound.