Background and purpose:
Recently, the use of inhaled insulin formulations for the treatment of type I and type II diabetes has been approved in Europe and in the United States. For regular use, it is critical that airway function remains unimpaired in response to insulin exposure.
We investigated the effects of insulin on airway smooth muscle (ASM) contraction and contractile prostaglandin (PG) production, using guinea-pig open-ring tracheal smooth muscle preparations.
It was found that insulin (1 nM-1 μM) induced a concentration-dependent contraction that was insensitive to epithelium removal. These sustained contractions were susceptible to inhibitors of cyclooxygenase (indomethacin, 3 μM), Rho-kinase (Y-27632, 1 μM) and p42/44 MAP kinase (PD-98059, 30 μM and U-0126, 3 μM), but not of PI-3-kinase (LY-294002,10 μM). In addition, insulin significantly increased PGF2α-production which was inhibited by indomethacin, but not Y-27632. Moreover, the FP-receptor antagonist AL-8810 (10 μM) and the EP1-receptor antagonist AH-6809 (10 μM) strongly reduced insulin-induced contractions, supporting a pivotal role for contractile prostaglandins.
Conclusions and implications:
Collectively, the results show that insulin induces guinea-pig ASM contraction presumably through the production of contractile prostaglandins, which in turn are dependent on Rho-kinase for their contractile effects. The data suggest that administration of insulin as an aerosol could result in some acute adverse effects on ASM function.