Dietary omega-3 fatty acids and cholesterol modify desaturase activities and fatty acyl constituents of rat intestinal brush border and microsomal membranes of diabetic rats.

The diabetes-associated changes in intestinal uptake of nutrients are modified by isocaloric alterations in the type of dietary lipids, and is associated with alterations in the phospholipid and fatty acyl content of the intestinal brush border membrane. We wished to test the hypothesis that diet- and diabetes-associated changes in brush border membrane phospholipid fatty acids are due to alterations in the activity of enterocyte microsomal delta-5, delta-6 and delta-9 desaturases. Adult female Wistar rats were divided into two groups. In half of the animals, diabetes was produced with the injection of streptozotocin, and the other half of the animals served as nondiabetic controls. Both groups were raised on chow for two weeks and were then randomized to one of four semisynthetic diets for two weeks: beef tallow low in cholesterol (BT), beef tallow high in cholesterol (BTC), fish oil low in cholesterol (FO), or fish oil high in cholesterol (FOC). Feeding a high cholesterol diet increased the activity of jejunal enterocyte microsomal membrane activity of delta-5 and delta-9-desaturases when fed with FO in non-diabetic control rats, increased delta-5-desaturase in diabetic rats fed FO, and increased the ileal activity of delta-5 and delta-6-desaturases in control and diabetic animals fed FO. Dietary fatty acids, cholesterol and diabetes did not produce the changes in the amount of fatty acids in BBM phosphatidylcholine or phosphatidylethanolamine expected from the measured alterations in delta-5 (20:4 omega 6 and 20:5 omega 3), in delta-6 (18:3 omega 6 and 18:4 omega 3), or in delta-9 desaturase (18:1 omega 9 and 16:1 omega 7). In summary, 1) the activities of enterocyte microsomal membrane delta-5, delta-6 and delta-9-desaturases are independently influenced by dietary fatty acids or cholesterol, or by diabetes; 2) changes in dietary fatty acids, cholesterol and diabetes are associated with alterations in the fatty acyl constituents of brush border membrane phosphatidylcholine and phosphatidylethanolamine, but these fatty acyl changes are not explained on the basis of variations in the activities of the microsomal desaturases. Thus, the intestinal brush border membrane and the enterocyte microsomal desaturases are capable of adapting in response to changes in dietary lipids or diabetes, but the two alterations are not necessarily causally interrelated.