Lipolysis in adipocytes isolated from deep and superficial subcutaneous adipose tissue

Abdominal subcutaneous adipose tissue (SAT) occurs in two depots separated by a fascial plane: deep SAT and superficial SAT. In a recent study it was demonstrated that the amount of deep SAT has a much stronger relationship to insulin resistance than does superficial SAT. Because insulin resistance may be related to fatty acid release from adipose tissue, we hypothesized that the two SAT depots may have a different lipolytic activity.

To test this hypothesis, we obtained samples of deep and superficial SAT from patients undergoing elective abdominal surgery. The rate of lipolysis was determined in the collagenase-digested adipocytes obtained from the two fat depots by measuring glycerol release in the presence and absence of isoproterenol. In addition, the relative concentration of hormone-sensitive lipase was determined in both SAT depots by Western blot analysis.

Our results showed that the rate of isoproterenol-stimulated lipolysis was approximately 20% higher in cells from deep SAT compared with those from superficial SAT, indicating that the deep SAT is more lipolytically active. The concentration of hormone-sensitive lipase did not differ between the two adipose tissue depots.

These findings suggest that the higher lipolytic activity of deep SAT may account for its stronger association with insulin resistance. The mechanism seems to be independent of differences in hormone-sensitive lipase concentration.