The effect of essential fatty acid deficiency on the stimulation of intestinal calcium transport by 1,25-dihydroxyvitamin D3.
The effect of altering the lipid composition of the brush-border membrane on the ability of 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) to stimulate calcium transport across the intestinal mucosa was examined by raising chicks on a vitamin D, essential fatty acid-deficient diet (-DEFAD) and measuring calcium absorption from duodenal sacs in situ and calcium uptake into brush-border membrane vesicles in vitro. Administration of 1,25-(OH)2D3 to -DEFAD and to -D control chicks led to the same increase in calcium transport in situ, whereas calcium transport in isolated brush-border membrane vesicles was not stimulated in the EFAD group, but responded normally in the control group. When the incubation temperature was increased to 34 degrees C, brush-border membrane vesicles from 1,25-(OH)2D3-treated essential fatty acid-deficient (+DE-FAD) chicks accumulated calcium at a faster rate than did vesicles from -DEFAD chicks. There was a marked decrease in the linoleic acid content and an increase in the oleic acid content of both the total lipid extract of the brush-border membrane as well as the phosphatidylcholine and phosphatidylethanolamine fractions, which could explain the temperature sensitivity of the in vitro system. When the diet of the EFAD chicks was supplemented with linoleic acid, the rate of calcium uptake into subsequently isolated vesicles from +DE-FAD chicks correlated with the amount of linoleic acid in the brush-border membranes. These results support the concept that the action of 1,25-(OH)2D3 on membrane lipid turnover and structure plays a critically important role in the 1,25-(OH)2D3-mediated cellular transport responses.
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism*; D002645:Chickens; D005228:Fatty Acids, Essential / Q000172:deficiency*; D007422:Intestines / Q000648:ultrastructure*; D019787:Linoleic Acid; D008041:Linoleic Acids / Q000032:analysis; D008871:Microvilli / Q000032:analysis / Q000378:metabolism; D014808:Vitamin D Deficiency / Q000378:metabolism
D005228:Fatty Acids, Essential; D008041:Linoleic Acids; D019787:Linoleic Acid; D002117:Calcitriol; D002118:Calcium