Abstract

Subcutaneous insulin absorption kinetics were assessed in 50 healthy study subjects (21 female, 29 male; age 26 +/- 3 years, BMI 22.5 +/- 1.8 kg/m2; mean +/- SD) during 45 min after periumbilical injection of soluble human U40- or U100-insulin (0.15 IU/kg). Subcutaneous fat thickness was measured by ultrasound, and skin temperature at the injection site was registered. Serum insulin concentrations increased within 30 min from basal values of 37 +/- 15 to 140 +/- 46 pmol/l after U40-insulin and from 36 +/- 10 to 116 +/- 37 pmol/l after U100-insulin (p < 0.001). After 45 min serum insulin concentrations were 164 +/- 43 pmol/l with U40-insulin and 128 +/- 35 pmol/l with U100-insulin (p < 0.001). Decline in blood glucose levels and suppression of C-peptide were comparable. The serum insulin levels reached 30 and 45 min after U40- and U100-insulin injection were positively correlated with skin temperature (p < 0.0008), and negatively correlated with subcutaneous fat thickness (p < 0.009). In conclusion, the lower insulin concentration of U40-insulin, higher skin temperature, and a thinner subcutaneous fat tissue at the injection site are associated with accelerated and enhanced subcutaneous insulin absorption.