Uptake of triglyceride fatty acids in adipose tissue in vivo in man

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Abstract
Currently available information on adipose tissue metabolism in man is mainly based on studies in vitro. In the present work adipose tissue lipid uptake was studied in vivo in man. 100 g glucose and 120 g milk fat with 10 μCi U-14C oleic acid were given in the overnight fasting state to eight women and 2 h after a carbohydrate-rich meal to eight women. After 4 h, 1-day, 1 week and 1 month radioactivity levels were determined in the lipids of adipose tissue in the femoral and abdominal regions and in plasma. At 4 h 30 and 20% of the oleic acid was estimated to remain in the extracellular space in the fasted and fed groups respectively, measured in plasma. Contents of oleic acid radioactivity was higher in the abdominal than femoral region. An estimated 27 and 46 g of fat was taken up in adipose tissue of the fasted and fed groups, constituting 1/3 and 1/2 of total tissue uptake respectively. After 1 day these figures were 43 and 60 g respectively. At 1 week and 1 month adipose tissue radioactivity was increasing slowly. Lipoprotein lipase (LPL) activity in adipose tissue at 4 h was higher in the femoral than abdominal adipose tissue and higher in the fed than fasted state in the abdominal region. A significant correlation was found between uptake and LPL in abdominal adipose tissue only. These results show that uptake of fat measured in vivo is probably not necessarily reflected by LPL measurements only, suggesting other regulatory factors. The results also suggest that priming of adipose tissue mechanisms for lipid uptake requires some period of time. Primary storage in tissues other than in adipose tissue is probably slowly, partially transferred to adipose tissue.