Histological organization of intestinal villi in the crocodilian caiman yacare (Daudin, 1802) during dietary lipid absorption
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Intestinal villi of Caiman yacare form longitudinal folds instead of the finger-like projections of most birds and mammals. Moreover, they lack Crypts of Lieberkühn 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 Lieberkühn. 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 Lieberkühn, 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.
KeywordsIntestinal villi Crypt of Lieberkühn Proliferative intestinal stem cells Lipid absorption Non-avian sauropsids Crocodilian
The authors would like to thank: COOCRIJAPAN (Cooperativa dos Criadores de Jacaré-do-Pantanal) for donating the animals used in the experiments and for sharing the facilities; Fundação de Amparo à Pesquisa do Estado de Mato Grosso (FAPEMAT) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)/São Paulo Research Foundation for supporting this work.
This work was supported by Fundação de Amparo à Pesquisa do Estado de Mato Grosso (FAPEMAT) contract Grant Number 715823/2008 and by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)/São Paulo Research Foundation contract Grant Number 2010/04527-5. RMB has received a scholarship from FAPESP, contract Grant Number 09/52884-4.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving animals were in accordance with the ethical standards of the institution or practice at which the studies were conducted. Animal handling and experimentation were approved by the committee on animal welfare and ethical experimentation from Institute of Biomedical Sciences, University of Sao Paulo (Protocol Number 131, page 110, book 02; issued September 20th, 2011) and by Brazilian environmental agency (ICMBIO/MMA/SISBIO: authorization number 30509-2; issued August 30th, 2011).
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