AJP - Gastrointestinal and Liver Physiology, Vol 256, Issue 1 188-G197, Copyright © 1989 by American Physiological Society
Influence of distension on absorption and villous structure in rat jejunum
G. Holzheimer and D. Winne
Pharmakologisches Institut, Universitat Tubingen, Federal Republic of Germany.
In urethan-anesthetized rats the appearance rates of urea (U), antipyrine
(A), and alpha-methyl-D-glucoside (MG) in the venous blood of perfused
jejunal segment were measured in the undistended state and after elevation
of the intraluminal pressure up to 10 cmH2O. Serosal and inner cylindrical
surface area of the jejunal segment were enlarged by maximally 100 and
150%, respectively. The absorption rates, however, increased only by 34
(U), 28 (A), and 26% (MG). The increase of the supravillous diffusion
resistance contributed only partially to this effect. The "cylindrical"
permeability coefficient (Pcyl, average permeability coefficient related to
inner cylindrical area, neglecting villous structure) decreased by 39, 57,
and 50%, respectively. Due to circular stretching, broad intervillous
spaces were formed that covered finally approximately 40% of the mucosal
surface area. The additional intervillous diffusion resistance in these
spaces was more effective than the absorption through the lateral surface
of the villi. Thus the overall permeability of the mucosa, i.e., Pcyl, was
reduced. Calculations based on a simplified model of the mucosa confirmed
the experimental results.
