Because dietary n-3 polyunsaturated fatty acids (n-3 PUFA) from fish oils have profound effects on lipid metabolism, we examined whether they influence the growth of adipose tissue at different locations in growing rats. Rats were fed for 4 wk on high-fat (HF) diets (20% fat) containing very low (L), medium (M), and high (H) amounts of n-3 PUFA but similar amounts of saturated fatty acids and n-6 PUFA. A fourth group was fed a standard laboratory diet (control group) to estimate changes in adipose tissue mass related to growth. At the end of the dietary treatment, the lipid mass (LM) of the four major adipose depots (subcutaneous, SC; mesenteric, MES; retroperitoneal, RP; epididymal, EPI) and total adiposity were significantly higher in each of the three HF groups than in the control group. The lipid gain in EPI was due to fat cell hypertrophy alone, whereas RP showed both hypertrophy and hyperplasia. Energy intake, fatty acid excretion, and body mass were the same in the three groups fed HF diets. Similarly, there was no difference in the LM or in lipid gains specifically caused by HF feeding of SC and MES between the HF groups. In contrast, the LM of RP was significantly lower in the H than in the L and M groups (50 and 30%, respectively). The LM of EPI was also 30% lower in the H than in the L group.(ABSTRACT TRUNCATED AT 250 WORDS)
The objective of the present study was to investigate the mobilization of individual fatty acids from human white fat cells. Mammary adipose tissue from eight healthy non-obese women in their normal dietary state was collected, and isolated adipocytes were incubated with lipolytic agents. The mobilization of 34 individual fatty acids was measured by comparing the composition of non-esterified fatty acids (NEFA) with that of the triacylglycerols (TAG) from which they originated through lipolysis. Compared with TAG, NEFA were enriched in some polyunsaturated fatty acids with 18-20 carbon atoms. Conversely, the percentage of very-long-chain (20-22 carbon atoms) saturated and monounsaturated fatty acids was approx. 2 times lower in NEFA than in TAG. The relative mobilization (% in NEFA/% in TAG) of the most readily mobilized fatty acid (C20:5, n-3; 2.25) was more than 6-fold higher than that of the least readily mobilized (C22:1,n-11; 0.37). Relationships were found between the molecular structure of fatty acids and their mobilization rate. For a given chain length, the relative mobilization rate increased with increasing unsaturation, whereas for a given unsaturation, it decreased with increasing chain length. The relative mobilization rate for essential fatty acids decreased in the following order: C20:5,n-3>C20:4,n-6>C18:3,n-3>C18:2, n-6>C22:6,n-3. Interestingly, C20:5,n-3 and C20:4,n-6, which are respectively precursors of the 3- and 2-series of prostaglandins, were preferentially mobilized. It is concluded that fatty acids are selectively mobilized from human fat cells according to molecular structure, in full agreement with animal studies. By modulating the qualitative fatty acid supply to organs and by remodelling the fatty acid composition of adipose tissue, this selectivity would be relevant for consideration in physiology, health and epidemiology.
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