Free-insulin profiles after intraperitoneal, intramuscular, and subcutaneous insulin administration

The aim of our study was to compare the time course of plasma free-insulin appearance after injection of equal amounts of insulin into the peritoneal cavity above and below the transverse mesocolon, intramuscularly, and subcutaneously. Seven nondiabetic subjects undergoing cholecystectomy received in random sequence 0.2 IU/kg of insulin into the peritoneal cavity above or below the transverse mesocolon. Concentrations of plasma free insulin were compared with those obtained from seven other nondiabetic subjects after repeated injections of equal amounts of insulin intramuscularly and subcutaneously. Intraperitoneal insulin above the transverse mesocolon yielded a faster rise of free insulin, peaking at 15 min, whereas intraperitoneal insulin below the transverse mesocolon produced a somewhat slower rise, peaking at 30 min. The area under the curves between 0 and 15 min was greater after the injection above than below the transverse mesocolon (P less than .05). Intramuscular and subcutaneous insulin injections resulted in a slower rise of plasma free insulin, peaking at 60 and 90 min, respectively. We conclude that the pattern of insulin appearance in the plasma resembles more closely physiologic events after intraperitoneal than after subcutaneous or intramuscular insulin administration.