Rapid Effects of the Intravenous Injection of a Medium-chain Triglyceride: Fish Oil Emulsion on the Triglyceride Fatty Acid Pattern of Soleus Muscle from ω3 Fatty Acid-depleted Rats

Abstract

Second generation rats depleted in long-chain polyunsaturated ω3 fatty acids display several features of the metabolic syndrome, including visceral obesity, liver steatosis, insulin resistance, hypertension, and cardiac hypertrophy. In the framework of an extensive study on such metabolic, hormonal and functional perturbations, the phospholipid fatty acid pattern and ex vivo metabolism of d-glucose were recently investigated in the soleus muscle of these ω3-depleted rats. The present study deals with the triglyceride fatty acid content and pattern of the soleus muscle in control animals and ω3-depleted rats. Some of the latter rats were injected intravenously 60-120 minutes before sacrifice with either an ω3 fatty acid-rich medium-chain triglyceride/fish oil emulsion (ω3-FO rats) or a control medium-chain triglyceride/olive oil emulsion (ω3-OO rats). The total fatty acid content of triglycerides was comparable in control and ω3-depleted rats and, in both cases, inversely related to their C20:4ω6 relative content. At variance with the situation found in control rats, no long-chain polyunsaturated ω3 fatty acid (C18:3ω3, C20:5ω3, C22:5ω3, C22:6ω3) was detected in the ω3-depleted rats. Unexpectedly, the triglyceride content in most long-chain polyunsaturated ω6 fatty acids (C18:2ω6, C20:3ω6, C20:4ω6 and C22:4ω6) had also decreased in the latter rats. Moreover, the activity of Δ9-desaturase was apparently increased in the ω3-depleted rats, as judged from the C16:1ω7/C16:0 and C18:1ω9/C18:0 ratios. The ω3-FO rats differed from ω3-OO rats by a lower contribution of C18:2ω6 metabolites (C18:3ω6, C20:3ω6, C20:4ω6 and C22:4ω6). These findings indicate that the prior injection of the medium-chain triglyceride/fish oil emulsion, known to increase the muscle phospholipid content in long-chain polyunsaturated ω3 fatty acids, may nevertheless accentuate the depletion in long-chain polyunsaturated ω6 fatty acids otherwise found in the triglycerides of ω3-depleted rats. Such a dual effect is reminiscent of that observed, under the same experimental conditions, for selected variables in d-glucose metabolism in the soleus muscle.

Keywords

long-chain polyunsaturated ω3 fatty acid-depleted rats - soleus muscle triglyceride fatty acid pattern - medium-chain triglyceride/fish oil emulsion

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