Effects of dietary fats on red blood cell membrane insulin receptor in normo- and hypercholesterolemic miniature swine

It has been demonstrated that the type of dietary fat affects insulin recep tors in various tissues in normal humans and animals by altering membrane f luidity. This study compares the effects of n-3 fatty acids from fish oil a nd n-6 fatty acids from corn oil on red blood cell membrane insulin recepto rs in normal and hypercholesterolemic minipigs. A group of minipigs were ma de hypercholesterolemic by feeding cholesterol and lard for 2 months; the o ther group served as controls and was fed stock diet. Both groups were then fed experimental diets containing either com. oil or menhaden oil or a mix ture of the two for 23 additional weeks. Blood was collected at 0, 2, 12 an d 23 weeks after the start of the experimental diets and membranes were pre pared from the red blood cells. Insulin binding to red blood cell membranes was measured by radioreceptor assay. Plasma insulin was measured by radioi mmunoassay. Insulin binding to red blood cell membrane was compared with th e fluidity of the membrane measured and reported earlier. There was no sign ificant effect of cholesterol feeding on plasma insulin concentrations. Aft er 23 weeks on experimental diet plasma insulin was significantly higher in minipigs fed menhaden oil compared to those fed com. oil. No such effect w as observed in hypercholesterolemic minipigs. No significant effect of eith er hypercholesterolemia or fish oil was observed on red blood cell insulin binding. A significant negative relationship was observed between insulin b inding and anisotropy at 4 degreesC for all probes but at 37 degreesC signi ficant negative relationship was observed only with polar probes. The data suggest that n-3 fatty acids from fish oil significantly increases plasma i nsulin in minipigs compared to n-6 fatty acids from com oil. However, the u nsaturation has no significant effect on insulin receptors on erythrocytes. Similarly, prior hypercholesterolemic state also has no effect on plasma i nsulin levels or the insulin binding to red blood cell membranes. (C) 2001 Elsevier Science Inc. All rights reserved.