Abstract
The aim of this study was to investigate the influence of feeding and UVB exposition on the occurrence and distribution patterns of vitamin D receptors (VDR) and calbindin D28k (Cb-D28k) in the gastrointestinal tract of veiled chameleons. Thus, 56 hatchlings were divided into 6 treatment groups: UV (with UVB exposure); No (no supplements); CaAUV (with calcium (Ca), vitamin A (vitA), UVB exposure); CaA (Ca, vitA); CaADUV (Ca, vitA, vitD, UVB exposure); CaAD (Ca, vitA, vitD) and reared for 6 months on locust-based diets. Finally, tissue sections of stomach, duodenum, ileum and colon were stained immunohistochemically (IHC) against Cb- D28k or VDR and assessed semi-quantitatively. VDR stained stronger in the luminal epithelium of duodenum than ileum, with more intense signals localized at the base of the villi when compared with the tip. Cb-D28k was mostly targeted to the luminal epithelium of the duodenum. In CaADUV and CaAD (groups with all supplements) Cb-D28k staining was stronger than in UV group. The important role of duodenum in the active transcellular absorption of Ca in veiled chameleons is suggested. Whereas the expression of Cb-D28k seems to be regulated by dietary supplementation with vit. D and A, the expression of VDR appears higher in animals not supplemented with Ca or vit D and A. The latter may be due to the decreased Ca concentrations, causing mobilization of vitamin D in the skin of animals exposed to UVB only.
Haxhiu, Driton