[Duodenal enterocyte ultrastructure of rats fed different amounts of vitamin D]

Deficiency of vitamin D, responsible for impaired absorption of calcium in rat small intestine, did not affect the activity of saccharase (marker enzyme of microvilli) in homogenate of intestinal epithelium and in an isolated fraction of microvilli. Content of lipid phosphorus per mg of protein in the microvilli of rats, deficient in vitamin D, was decreased by 30% as compared with the control animals. Deficiency of vitamin D was accompanied by alterations in ultrastructure of 10-15% of enterocytes from small intestine. These alterations consisted in more widely spaced arrangement of microvilli, their fragmentation into separate vesicles with liberation of apical cellular surface, swelling of mitochondria with reduction of their crysts, enlargement of rough endoplasmic reticulum cisterns. The layer of glycocalix on the microvilli was decreased or completely disappeared in most enterocytes. The impairments found in submicroscopic organization of enterocytes might constitute the morphologic basis for the disturbed calcium absorption in the intestine under conditions of vitamin D deficiency.