Article

Regulation of free fatty acid metabolism by insulin in humans: Role of lipolysis and reesterification

Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-2230.
The American journal of physiology (Impact Factor: 3.28). 12/1992; 263(6 Pt 1):E1063-9.
Source: PubMed

ABSTRACT

The regulation of lipolysis, free fatty acid appearance into plasma (FFA R(a)), an FFA reesterification and oxidation were examined in seven healthy humans infused intravenously with insulin at rates of 4, 8, 25, and 400 mU.m-2.min-1. Glycerol and FFA R(a) were determined by isotope dilution methods, and FFA oxidation was calculated by indirect calorimetry or by measurement of expired 14CO2 from infused [1-14C]palmitate. These measurements were used to calculate total FFA reesterification, primary FFA reesterification occurring within the adipocyte, and secondary reesterification of circulating FFA molecules. Lipolysis, FFA R(a), and secondary FFA reesterification were exquisitely insulin sensitive [the insulin concentrations that produced half-maximal suppression (EC50), 106 +/- 26, 91 +/- 20 vs. 80 +/- 16 pM, P = not significant] in contrast to insulin suppression of FFA oxidation (EC50, 324 +/- 60, all P < 0.01). The absolute rate of primary FFA reesterification was not affected by the increase in insulin concentration, but the proportion of FFA molecules undergoing primary reesterification doubled over the physiological portion of the insulin dose-response curve (from 0.23 +/- 0.06 to 0.44 +/- 0.07, P < 0.05). This served to magnify insulin suppression of FFA R(a) twofold. In conclusion, insulin regulates FFA R(a) by inhibition of lipolysis while maintaining a constant rate of primary FFA reesterification.

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    • "In contrast, plasma insulin concentration increased from 1.9 ± 0.4 μIU/L to 10.5 ± 3.1 μIU/L (P < 0.05) by 2 hr and to 7.6 ± 2.0 μIU/L (P < 0.05) by 6 hr in response to the saury meal and returned to the basal level by the end of the study (Figure 5b). It has been well documented that insulin plays a crucial physiological role in postprandial glucose homeostasis and in inhibiting adipose tissue lipolysis, which may lead to reduced release of fatty acids into the blood stream [16,17]. Thus, the hyperinsulinemia after the saury meal may have caused the observed acute decreases in plasma glucose and free fatty acids. "
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