INTERSTITIAL INSULIN DURING EUGLYCEMIC-HYPERINSULINEMIC CLAMP IN OBESE AND LEAN INDIVIDUALS

Transcapillary insulin transport has been considered a rate-limiting s tep of insulin action. However, direct measurement of interstitial ins ulin levels during physiologic levels of insulinemia have not been per formed. We determined changes in interstitial insulin in eight healthy non-obese men and seven healthy obese men by microdialysis during a e uglycemic-hyperinsulinemic clamp. Interstitial insulin was determined in the subcutaneous tissue of the abdomen and thigh. Steady-state insu lin concentrations were reached approximately 10 minutes after the sta rt of insulin infusion in the subcutaneous tissue of the abdomen and t high and returned to basal levels approximately 10 minutes after the i nfusion was discontinued. There was no difference in the rapidity of c hange in interstitial insulin between obese and lean individuals at ei ther site studied, irrespective of the pattern of fat distribution. Th e relative change in dialysate insulin concentration during the euglyc emic clamp did not differ between obese and lean individuals at either site studied. It was also unaffected by the waist to hip ratio. The r apid change in interstitial insulin concentration could be of physiolo gic significance in determining the effects of changes in circulating insulin concentration. We conclude that transcapillary insulin transpo rt in adipose tissue is unaffected by obesity and the pattern of fat d istribution in healthy men. It is also concluded that when interstitia l insulin is determined directly, transcapillary insulin transport is rapid and does not demonstrate a significant lag phase. Copyright (C) 1996 by W.B. Saunders Company