Histological organization of intestinal villi in the crocodilian caiman yacare (Daudin, 1802) during dietary lipid absorption

Abstract

Intestinal villi of Caiman yacare form longitudinal folds instead of the finger-like projections of most birds and mammals. Moreover, they lack Crypts of Lieberkuhn and the lamina epithelialis organization is dynamic, changing from pseudostratified to simple columnar epithelium after feeding. Because of these differences, we sought to verify whether intestinal villi of the crocodilian Caiman yacare are functionally compartmentalized along their length similarly to the finger-like villi that harbors Crypt of Lieberkuhn. For this, Caiman yacare were force-fed soybean oil, the intestinal mucosa was harvested and analyzed under light microscopy after lipid staining or immunohistochemistry for the proliferative marker PCNA. Functional compartmentalization was assessed by evaluating differences in lipid absorption along intestinal villi base-to-tip axis, by localizing the proliferative enterocytes and by verifying whether such cells were capable of absorbing lipids. Histological morphometric analyses of the extent of enterocyte hypertrophy caused by lipid inclusions and the contribution of such inclusions to histological remodeling from pseudostratified to simple columnar epithelium were also evaluated. Although lacking Crypts of Lieberkuhn, enterocytes present at villi base were PCNA positive and devoid of the great amount of lipid inclusions observed in the other intestinal villi domains, in a similar pattern to finger-like villi. Enterocytes doubled their volume because of lipid inclusions, and in spite of such enterocyte hypertrophy, lamina epithelialis continued to be pseudostratified within lateral sides, whereas villi tip were organized in a simple columnar epithelium.