The effect of dietary protein, either casein (CAS) or soybean protein (SOY), on the polyunsaturated fatty acid (PUFA) composition of liver microsomal phospholipids and eicosanoid production was compared in normal and streptozotocin-induced diabetic rats fed diets containing perilla oil rich in alpha-linolenic acid. In normal rats the linoleic acid desaturation index in liver microsomal phospholipids was significantly higher in the CAS group than in the SOY group, whereas it was reversed in diabetic rats. The proportion of eicosapentaenoic acid (EPA) decreased in diabetic rats, in particular those fed SOY, whereas it was vice versa for arachidonic acid (AA). The ratio of aortic prostacyclin production to platelet thromboxane A2 production decreased only in diabetic rats fed SOY reflecting a reduction of the EPA/AA ratio. Thus, dietary protein differently modified the PUFA composition and eicosanoid balance even in the diabetic rat. In this respect, alpha-linolenic acid seemed to be less influential than linoleic acid.
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Ikeda et al. (1993) studied this question.