In vivo subcutaneous adipose tissue glucose kinetics after glucose ingestion in obesity and fasting

Abstract

The kinetic pattern of subcutaneous adipose tissue extracellular glucose following glucose ingestion was investigated in vivo with a microdialysis technique in normal-weight (n=21) and obese subjects (n=18) before and after a 7-day fast (n = 9). A dialysis probe (4×0.5 mm) was implanted subcutaneously, and was continuously perfused (5 μl/min). The tissue dialysate glucose concentration was determined in 15-min samples before and during a period of 180 min after a 75-g oral glucose load. A comparison was made between the tissue dialysate concentrations and the venous blood glucose levels. In all study groups the increase in subcutaneous tissue dialysate glucose following glucose ingestion paralleled that in blood, with a time-lag of up to 15 min. In the normal-weight subjects the maximum relative increase in abdominal adipose tissue dialysate glucose was 25% higher (p <0.005) than the corresponding blood glucose level, and the total relative glucose level (area under curve, AUC) in abdominal fat was 20% (p<0.01) higher than in blood. In contrast, the kinetics of gluteal subcutaneous tissue dialysate and blood glucose levels were similar. In the obese patients before the fasting period the maximum relative glucose level in abdominal fat was almost twice as high as in blood (p<0.005), and the total glucose level (AUC) was 50% higher than the blood glucose AUC (p<0.005). After the fast, on the other hand, almost identical relative dynamics of abdominal subcutaneous tissue and blood glucose levels were found. It is concluded that ingested glucose is rapidly distributed to the interstitial compartment of subcutaneous adipose tissue. In normal-weight subjects the hexose is retained to some extent in the abdominal, but not in the gluteal, fat depot, which indicates regional differences in subcutaneous tissue glucose kinetics following glucose ingestion. In obesity the accumulation of glucose in abdominal fat is markedly increased, whereas after fasting the abdominal subcutaneous tissue glucose level closely resembles the venous blood glucose level. It remains to be elucidated whether the observed effects of obesity and fasting on the handling of glucose by adipose tissue following glucose ingestion are due to changes in subcutaneous tissue blood flow and/or tissue glucose utilization.

Key Words:

• fat cell
• interstitial fluid
• microdialysis