Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were distributed mainly in the sn-1,3 positions of seal oil triglyceride and in the sn-2 position of squid oil triglyceride. Seal oil-rich or squid oil-rich fats having constant saturated/monounsaturated/polyunsaturated fatty acid (PUFA) and n-6/n-3 PUFA ratios were fed to exogenously hypercholesterolemic rats for 1 60 d. The control fat contained linoleic acid as the sole PUFA. Before starting the experimental diets, rats were orally treated with high doses of vitamin D for 4 d to accelerate atherogenesis. The percentage of arachidonic acid in phosphatidylcholine and phosphatidylethanolamine of liver, platelets, and aorta was lower in the marine oil groups than in the control group, seal oil being more effective than squid oil. Maximal platelet aggregation induced by collagen was significantly lower in both marine oil groups. Platelet thromboxane (TX) A2 production induced by collagen or thrombin was markedly reduced by feeding seal or squid oils, the reduction being more pronounced in the seal oil than in the squid oil group. Aortic prostacyclin (PGI2) production was the same among the three groups. The ratio of the productions of aortic PGI2 and platelet TXA2 was significantly higher in the seal oil than in the control group. Although there was no difference in intimal thickness among the three groups, the aortic cholesterol content was significantly lower in the marine oil groups than in the control group. These results showed that the main effects in rats of the different intramolecular distributions of EPA and DHA in dietary fats were on arachidonic acid content in tissue phospholipids and on platelet TXA2 production.
1In order to examine the role of airway epithelium in the responsiveness of smooth muscle in man, we measured the contractile responses to acetylcholine (ACh), histamine, and prostaglandin F2, (PGF2,) and the relaxation response to isoprenaline (Isop), in 48 bronchi obtained from 10 patients who received surgery. Responses were measured in the presence and absence of the epithelium. 2 Removal of epithelium (by rubbing the mucosa gently with forceps) significantly increased the contractile responses evoked by ACh, histamine and PGF2,.3 In contrast, removal of epithelium did not alter the relaxation response to Isop. 4 To clarify the mechanism underlying this epithelial inhibitory effect on smooth muscle contraction, we measured the contractile responses of dog trachea with the epithelium removed to increasing concentrations of ACh. After measuring the control response, we added about 0.1 g of the chopped epithelium in the organ chamber, and measured the response again. 5 After adding airway epithelium and incubating with tracheal strips, the contractile response of tracheal strips decreased significantly as compared to the control response. 6 These results show that airway epithelium possesses the ability to decrease the smooth muscle contraction to ACh, histamine and PGF2X in man and dogs.7 The mechanism of this inhibitory effect of the airway epithelium is not explained by a change in mechanical property of the airway nor the change in diffusion of these drugs to the smooth muscle across the epithelium. Thus, these results suggest that airway epithelium may have an important role in modulating smooth muscle tone, possibly by inactivation of these mediators, or by releasing an epithelium-derived relaxing factor.
SummaryEicosapentaenoic and docosahexaenoic acids were distributed mainly in the sn-1 and 3 positions of seal oil triacylglycerols and in the sn-2 position of fish oil triacylglyc erols. Seal oil-rich or fish oil-rich fats having constant polyunsaturated (PUFAs)/monoun saturated/saturated fatty acids and n-6/n-3 PUFAs ratios were fed to hamsters for 3 weeks. The control fat contained linoleic acid as the sole PUFA. The concentration of triacylglyc erols in the liver was significantly lower in the fish oil group than in the control group. Phospholipid concentration in serum was lower and that in the liver was higher in the seal oil group compared with the fish oil group. The activities of fatty acid synthase (FAS), glu cose-6-phosphate dehydrogenase (G6PDH), and the malic enzyme were significantly lower in both the fish and seal oil groups than in the control group. Dietary seal oil more effec tively reduced arachidonic acid content in liver phosphatidylcholine and phos phatidylethanolamine and serum phosphatidylcholine than fish oil. These results showed that different intramolecular distribution of n-3 PUFAs influenced glycerolipid metabolism and arachidonic acid content in serum and liver phospholipids of hamsters. Key Words eicosapentaenoic acid, docosahexaenoic acid, fatty acid synthesis, seal oil, hamster It has been well established that eicosapentaenoic (EPA) and docosahexaenoic acids (DHA) have beneficial physiological effects in humans and animals (1-3). Seal oil contains EPA and DHA mainly at the sn-1 and 3 po sitions of the triacylglycerols. We previously reported in rats that plasma and liver triacylglycerol concentrations were more effectively reduced by dietary seal oil than by fish oil in which EPA and DHA are mainly distributed at the sn-2 position of the triacylglycerols. The predomi nant effect of seal oil was ascribed to the suppression of fatty acid synthesis in the liver (4). Seal oil also more ef fectively lowered arachidonic acid content in phospho lipids of various tissues in rats (4, 5). These results sug gest that structural difference of EPA and DHA in tria cylglycerols may differently affect lipoprotein and lipid metabolism in rats. It has been known that rats are a poor animal model for human lipoprotein metabolism. They lack cholesterol ester transfer protein (CETP), and therefore they transport most plasma cholesterol in high density lipoprotein. In contrast to rats, hamsters transport plasma cholesterol mainly in the low density lipoprotein fraction, because they have CETP in plasma. However, there are only a few studies on the effect of marine oils on lipid metabolism in hamsters (6-9). In the present study, we examined the effect of seal and fish oils on lipid metabolism in hamsters.
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