104: Heme oxygenase in human myometrial cells and tissue

Abstract

MARTIN SLODZINSKI, Johns Hopkins University, Anesthesiology and Critical Care Medicine, Baltimore, Maryland OBJECTIVE: Heme oxygenase 1 (HO-1) has been extensively studied as an inducible stress response protein essential to heme metabolism. HO-1 may also be present in other systemic tissues and may in fact be inducible by non-heme substrates such as heavy metals, endotoxin, heat shock, inflammatory cytokines, and prostaglandins. Little is known regarding HO-1 and human myometrium. We postulate that HO-1 is critical for myometrial homeostasis and is instrumental in maintaining gravid uterine quiescence. STUDY DESIGN: With IRB approval, human myometrial tissue was obtained from the lower uterine segment of pregnant women undergoing cesarean delivery for pre-term and term labor. A western blot analysis was performed using polyclonal rabbit antibody (1:2000) to identify the presence of HO-1. Ratiometric imaging of intracellular calcium and isometric myometrial tissue force were measured in response to oxytocin and the competitive HO-1 inhibitor zinc protoporphyrin IX (PPN-9) and bilirubin. RESULTS: HO-1 is expressed in term and preterm human myometrial tissue. In primary cultured human myocytes, PPN-9 (10uM, 5minutes) inhibition of HO-1 irreversibly increased intracellular calcium. This increase was prevented if bilirubin (100uM) was applied with the PPN-9. In isometric myometrial contractions, PPN-9 (1nM)increased the amplitude and rate of contraction compared with controls. H202 (10uM-1mM) increased the amplitude of contraction in the PPN-9 more than the control tissue. Bilirubin partially abolished the H202 increase in amplitude. CONCLUSION: While extensive research has been performed regarding the function of HO-1 in heme degradation, HO-1 physiology is unexplored in human myometrium. Our investigation demonstrates that HO-1 is present within gravid myometrium and influences myometrial intracellular calcium homeostasis and myometrial tissue contractibility.