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In a previous study of glucose tolerance, plasma insulin levels were greatly elevated in genetically obese Wistar fatty rats but not lean rats fed a diet containing polyunsaturated fatty acids. In the present study, triacylglycerol-regulation of levels of circulating insulin and glucagon-like peptide-1 (7-36) (GLP-1) has been investigated in these rats. In the glucose tolerance test, the two plasma insulin peaks appeared in obese and lean rats intubated with glucose + corn oil, at 15- 30 min and 4 h, whereas only the first peak appeared in rats intubated with glucose alone, although the glucose response did not differ. After intubation of corn oil only, the insulin peak at 15 min was not detected but the peak at 4h was large. The two plasma GLP-1 peaks appeared 15 min and 4 h after intubation of glucose + corn oil similarly to the insulin responses, although the first peak was small and the second peak was very large. A small peak at 15 min was not significant in rats intubated glucose alone and no peak was seen at 4 h. The GLP-1 concentrations were significantly higher in the following order: portal vein > inferior vena cava > tail vein. The plasma GLP-1 increment in response to oral triacylglycerols was significantly higher in obese rats than in lean rats as was the insulin increment. Thus, oral triacylglycerols (possibly polyunsaturated) appeared to act at the gut lumen to stimulate GLP-1 secretion, which may be responsible for the second (4 h) insulin peak. [ABSTRACT FROM AUTHOR]

An examination was conducted of the time courses of incorporation of polyunsaturated fatty acids (PUFA) into lipids of plasma, liver and its nuclei, and the time courses of hepatic lipogenic enzyme gene expression after oral administration of perilla oil by a stomach tube to rats fed a fat-free diet. Linolenic acid, 18:3(n-3), and eicosapentaenoic acid, 20:5(n-3), were considered indices of exogenous fatty acids. In total lipids of liver and its nuclei, linolenic acid was detected 1 h after the intubation, continued to increase during the first 4 h, then decreased and almost disappeared by 48 h. Eicosapentaenoic acid also increased within only 1 h of intubation, reached a maximum after 8 h and then gradually decreased. In contrast with the increase of exogenous PUFA, the mRNA concentrations of hepatic lipogenic enzymes began to decrease 2 h after the perilla oil intubation, were at a minimum at 8 h, and then increased. In another experiment to examine the effects of dietary perilla oil concentration on PUFA incorporation and gene expression, rats were given diets containing 0-10% perilla oil (supplemented with hydrogenated fat to 10% fat) for 3 d. Only 1% perilla oil elevated the exogenous PUFA concentrations in liver and its nuclei in comparison with concentrations in rats fed a hydrogenated fat diet. Perilla oil at 2% of the diet was sufficient to suppress lipogenic enzyme gene expressions, which were suppressed to the minimum level by 5% perilla oil in the diet. Thus, lipogenic enzyme gene expression was quickly suppressed by a small amount of exogenous PUFA, in contrast with the increase of PUFA incorporation into liver and its nuclei. Newly incorporated exogenous PUFA appear to be involved in suppression of lipogenic enzyme gene expression. [ABSTRACT FROM AUTHOR]