Abstract

Objective: To examine insulin's effect on the tissue glucose concentration at the site of subcutaneous insulin administration.

Research Design And Methods: A CMA-60 microdialysis (MD) catheter and a 24-gauge microperfusion (MP) catheter were inserted into the subcutaneous adipose tissue of fasting, healthy subjects (n=5). Both catheters were perfused with regular human insulin (100 U/ml) over a 6-h period, and used for glucose sampling and simultaneous administration of insulin at sequential rates of 0.33, 0.66, and 1.00 U/h (each rate was used for 2h). Before and after the insulin delivery period, both catheters were perfused with an insulin-free solution (5%-mannitol) for 2h, and used for glucose sampling only. Blood plasma glucose was clamped at euglycemic levels during insulin delivery.

Results: Start of insulin delivery with MD and MP catheters resulted in a decline of the tissue glucose concentration and the tissue-to-plasma glucose ratio for ∼60 min (p<0.05). However, during the rest of the 6-h period of variable insulin delivery, tissue glucose concentration paralleled the plasma glucose concentration and the tissue-to-plasma glucose ratio for MD and MP catheters remained unchanged at 83.2 ± 3.1 and 77.1 ± 4.8 %, respectively. After subsequent switch to insulin-free perfusate, tissue glucose concentration and tissue-to-plasma glucose ratio increased slowly and re-attained pre-insulin-delivery levels by the end of the experiments.

Conclusions: The results show the attainment of a stable tissue-to-plasma glucose ratio at the site of insulin administration, thus indicating that insulin delivery and glucose sensing may be performed simultaneously at the same adipose tissue site.