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Amounts of plasma lipids, apolipoprotein AI (apo AI) and apolipoprotein E (apo E) were measured in streptozotocin-induced diabetic rats. Plasma triglyceride and cholesterol levels of diabetic rats were not significantly different from those of control rats. Plasma apo AI levels of diabetic rats were significantly higher than those of control rats (78.2 +/- 29.3 vs 27.2 +/- 3.4 mg/dl, P less than 0.001), while plasma apo E levels of diabetic rats were significantly lower than those of control rats (4.2 +/- 1.0 vs 13.9 +/- 5.3 mg/dl, P less than 0.001). Insulin treatment (12U/day) of diabetic rats decreased plasma apo AI levels significantly (treated: 32.8 +/- 3.4, untreated: 48.7 +/- 6.2, control: 28.5 +/- 2.4 mg/dl) and normalized plasma apo E levels (treated: 16.1 +/- 1.7, untreated: 5.4 +/- 0.7, control: 15.8 +/- 1.3). Insulin injection (4U/day) to normal rats did not cause any changes in both plasma apo AI and apo E levels. The data indicate that diabetes is not always accompanied by hyperlipidemia, however this inevitably carries apoprotein abnormalities characterized by the high plasma apo AI and low apo E levels, which are reversible with insulin treatment. The changes in the levels of plasma apo AI and apo E could be related to the development of atherosclerosis in diabetes.

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In an attempt to examine whether the VLDL secreted by diabetic rats may be different from that by normal rats, plasma obtained after Triton WR-1339 treatment was analyzed. After Triton treatment, a marked increase in plasma triglyceride levels with lesser increases in cholesterol and phospholipids was observed in both diabetic and control rats. The degree of such increases was almost equal between two groups of rats. The large increases in plasma lipid levels presumably reflect the increase in plasma VLDL fraction. The lipid composition of VLDL of diabetic rats was very similar to that of normal controls. The LDL fraction of diabetic rats was low in its contents of both cholesterol and phospholipids compared with that of normal controls. The composition of IDL and HDL in diabetic rats was similar to that of controls. From these data, we suggest that the VLDL of diabetic rats secreted under basal fasting condition is not different in its lipid composition as well as in amounts from that of controls.