Delayed transcapillary delivery of insulin to muscle interstitial fluid after oral glucose load in obese subjects.

Obese subjects exhibit a delay in insulin action and delivery of insulin to muscle interstitial fluid during glucose/insulin infusion. The aim of the present study was to follow the distribution of insulin to skeletal muscle after an oral glucose load in obese subjects. We conducted an oral glucose tolerance test (OGTT) in 10 lean and 10 obese subjects (BMI 23 +/- 0.6 vs. 33 +/- 1.2 kg/m(2); P < 0.001). Insulin measurements in muscle interstitial fluid were combined with forearm arteriovenous catheterization and blood flow measurements. In the obese group, interstitial insulin was significantly (35-55%) lower than plasma insulin (P < 0.05) during the 1st h after the OGTT, whereas in lean subjects, no significant difference was found between interstitial and plasma insulin levels during the same time period. The permeability surface area product for glucose, representing capillary recruitment, increased in the lean group (P < 0.05) but not in the obese group (NS). Obese subjects had a significantly higher plasma insulin level at 90-120 min after oral glucose (398 +/- 57 vs. 224 +/- 37 pmol/l in control subjects; P < 0.05). The significant gradient between plasma insulin and muscle interstitial insulin during the first hour after OGTT suggests a slow delivery of insulin in obese subjects. The hindered transcapillary transport of insulin may be attributable to a defect in insulin-mediated capillary recruitment.