Immunoreactive endomorphin 2 is generated extracellularly in rat isolated L4,5 dorsal root ganglia by DPP-IV.

Background and Aims: The gene(s) encoding for endomorphin precursor(s) is/are still unknown. We have raised the possibility of and did find some evidence for a potential de novo biosynthetic route starting from Tyr-Pro precursor. To pursue further this possibility we measured the generation of immunoreactive endomorphin-2 (E2-IR) in adult rat isolated L4,5 dorsal root ganglia.
Results and Conclusions: In rat isolated dorsal root ganglia the combination of presumed biosynthetic precursor of endomorphin 2 (E2), Tyr-Pro with the dipeptidyl peptidase IV (DPP-IV) inhibitor Ile-Pro-Ile generated 1.60+/-0.37 pg/mg Wet Tissue Weight_30 min E2-IR in the bathing fluid (n=4) with an 8-fold increase upon depolarization whereas the tissue content was low (0.50+/-0.08 pg/mg_WTW). Substance P, as determined by ELISA in the pilot experiments, was found almost exclusively within the tissues. It is concluded that E2-IR was generated extracellularly by a membrane-bound DPP-IV, which was switched to "synthase" mode by the hydrolase inhibitor Ile-Pro-Ile. DPP-IV was depolarization-sensitive in "synthase" functional mode.