Changes in the isoforms of the sodium pump in the placenta and myometrium of women in labor

Objective: We determined whether changes in sodium pump isoform abundance accompanied active human labor. Study Design: Specimens of placenta, amniochorion, and myometrium were collected from women in active spontaneous labor and from those not in labor. The abundance of the three sodium pump α-isoforms was determined by Western blot analysis. Results:Levels of the α1 and α2 isoforms were comparable in the three tissues for women in labor and not in labor. However, α3 isoform abundance in placenta and myometrium (but not amniochorion) was significantly decreased in women in active labor compared with women not in labor (sodium pump α3 in placenta: no labor 91.2 ± 27.6 vs labor 46.9 ± 3.6 density units, P = .002. Sodium pump α3 in myometrium: no labor 52.3 ± 7.7 vs labor 19.8 ± 1.6 density units, P = .0002). Conclusion: Because reductions in sodium pump number can result in hormone release from secretory tissues and in contraction of muscle, this suggests that the sodium pump may play a significant role in the initiation or maintenance of human labor. (Am J Obstet Gynecol 2003;188:759-64.)