The effect of corticosteroids on microvillous vesicles from the small intestine of adult rats: an automated, morphometric analysis.

The hypothesis that the corticosterone-induced enhancement of D-glucose uptake by brush-border membrane vesicles from the small intestine of adult rats is caused by an alteration in vesicle volume was tested by means of structural morphometric computerized analysis. By using a Ca2+ precipitation method, microvillous membrane vesicles were prepared from different groups of adult rats: normal controls; animals sacrificed 8 days after adrenalectomy; sham-operated pair-fed controls; animals treated with corticosterone (1 or 10 mg x 100 g b.wt.-1 daily i.p. for 8 days); corticosterone vehicle-treated controls. The vesicles were processed by conventional electron microscopy techniques. Morphometric computerized analysis was carried out on electron micrographs at a 20,000 x magnification, after selecting by an interactive method the vesicles showing certain morphologic features. The morphometric parameters determined for the vesicles from each experimental group were diameter, shape factor (minimal to maximal diameter ratio), surface area and volume. The following main findings were obtained: the vesicles were consistently spherical, with the glycocalyx on the outer side; sham-operation and pair-feeding with adrenalectomized rats, as well as corticosterone-vehicle injection, significantly reduced vesicular volume as compared to normal controls; adrenalectomy significantly decreased vesicular volume as compared to pair-feeding; excess of corticosteroids caused opposite changes (i.e. a significant increase of vesicle volumes as compared to vehicle injection), which were apparently dose-dependent. A comparison with D-glucose vesicular transport data previously obtained under the same experimental conditions revealed the existence of a positive relationship between vesicular volume and D-glucose half-filling time (t 1/2). A positive relationship between vesicular volume and D-glucose vesicular space was found for all experimental conditions except vehicle injection. As a whole, the morphometric results were consistent with functional findings, supporting our previous hypothesis that the corticosterone-induced increase in D-glucose transport by small intestinal microvillous vesicles is due, at least in part, to enlargement of the vesicle.