A model for transport of glucose in adipose tissue to a microdialysis probe.

A model is presented, describing diffusion of solutes (as glucose) through adipose tissue. The model is based on the well-known extraction equation for diffusion across capillary walls or across the membrane of microdialysis probes, but adapted for use in adipose tissue. Arguments are presented for a simple scheme in which the mean capillary concentration of a solute (i.e., glucose) is substituted for the interstitial fluid solute concentration in the extraction equation, as the driving force for diffusion of glucose from capillary to cell or from capillary to a microdialysis probe. The model is discussed by evaluating the results of previous studies by our group and others on the equilibrium concentration of glucose in a microdialysis probe, as well as the effect of insertion on recovery of glucose by the probe and the time it takes for glucose in adipose tissue to diffuse to the probe. The results of these studies are in good agreement with the predictions derived from the model: The equilibrium concentration of glucose in the microdialysis probe is equal to the capillary glucose concentration. Insertion effects can be explained by a lower glucose concentration around the probe because of inflammation (12-18 h) and by a slow increase in the number of functioning capillaries around the probe due to wound healing (4-6 days). Transport time of glucose from capillaries to a microdialysis probe is not more than a few seconds. Reported delay times in the literature are probably caused by an uneven distribution of blood glucose after a glucose challenge.