Effect of insulin concentration, subcutaneous fat thickness and skin temperature on subcutaneous insulin absorption in healthy subjects.

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.