Rates of depletion of linoleic acid from fat depots of selected lines of mice differing in growth rate and adiposity

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Abstract
Rates of depletion and half‐lives of linoleic acid from epididymal, subcutaneous and retroperitoneal fat pads and the residual body were compared among 5 genetically diverse strains of mice: M16, a polygenic obese line developed by selection for high postweaning gain; ICR, a control line from which M16 was derived; H6, a nonobese strain selected for large 6‐week body weight; L6, selected for small 6‐week body weight; and C2 a control line from which H6 and L6 were initiated. Rates of depletion and half‐lives of linoleic acid were obtained on a fat‐free diet following an enrichment period of feeding a diet high in linoleic acid. The M16 mice have an increased capability of synthesizing fat from carbohydrates as shown by a continued increase in fat depot weights when fed the fat‐free diet. The 4 other lines showed no subsequent increase in fat depot weights on the fat‐free diet. Rates of depletion of linoleic acid were significantly different among lines in each of the 4 depots. Ranking of lines for depletion rates was similar among the 3 discrete depots, but a more rapid rate of depletion was observed in subcutaneous and retroperitoneal fat depots than in the epididymal fat depot. Rates of depletion in line M16 were slower than in the ICR control line. Line H6 had a slower rate of depletion than line L6. Line L6 deviated more from the C2 control than did line H6, indicating an asymmetric correlated selection response. The decreased depletion rate of linoleic acid in fat tissue of M16 and H6 mice suggests the possibility that the turnover rates of fatty acids have been reduced in these lines as a result of a reduction in lipolytic activity. The increased depletion rate of linoleic acid in L6 mice suggests that selection for small body size has substantially increased the rate of fat turnover. The experiment demonstrates that genetic differences among lines in fat turnover have accurued as corelated responses to selection for growth rate.