Dietary lipid absorption and lipoprotein secretion by the intestine of the crocodilian Caiman yacare (Daudin, 1802)

Abstract

Although it is stated that dietary lipids are absorbed proximally in the small intestine of vertebrates, there are variations of the primary site for lipid absorption even when closely related species are considered. Moreover, there are evidences suggesting that the small intestine distal segments are equally capable of absorbing lipids, although it is not known whether it is the case for crocodilians. The lipoprotein assembling process and secretion routes are also largely unknown for crocodilians and therefore, assumed to be similar to mammals. The aims of this study were to identify the crocodilian Caiman yacare intestinal segments where lipid absorption occurs, to characterize the intestinal lipoproteins secreted by enterocytes and to evaluate lymphatic system contribution to exportation of lipoproteins from the intestine. For this, soybean oil was injected into C. yacare stomach and intestinal lipid absorption process was characterized by light and electron microscopy 24, 48 and 72 h after oil injection. The same amount of lipid inclusions was present in the duodenum, in the proximal jejunum and in the distal jejunum. The colon also showed a few lipid inclusions. The bulk of lipoproteins secreted by the enterocytes was <200 nm in diameter and was observed inside the lymphatic central lacteals. Lipid inclusions were absent from the intestinal mucosa and from the lacteals of the control animals. Finally, the high amount of lipids ingested did not recruit innate immune cells to the mucosa in any intestinal segment, suggesting that soybean oil is not pro-inflammatory for intestinal mucosa of C. yacare in the short time analyzed.