November 21 (HealthDay News) -- Researchers say they've found the switch that activates the uterine muscles for contraction during childbirth, a finding that may lead to therapies for preterm labor.

The molecule prostacyclin normally binds the protein IP on the surface of these uterine muscle cells, keeping them relatively inactive during pregnancy.

But researchers from Dartmouth Medical School in New Hampshire, testing uterine tissue strips from pregnant women undergoing Caesarean birth, found that agonist chemicals can stimulate IP, which then activated proteins involved in muscle contraction. The same chemicals also increased the contraction of these tissue strips in response to the hormone oxytocin.

The findings were published in the latest issue of the Journal of Clinical Investigation.

In an accompanying commentary, researchers from Newcastle University in the United Kingdom said the finding might be viewed as contentious, because prostacyclin is a smooth muscle relaxant. They explained the paradoxical observation by saying that one of the major signaling molecules produced by the uterus just prior to labor is prostacyclin.

SOURCE: The Journal of Clinical Investigation, news release, Nov. 20, 2008