So far, the scientists -- who work at the University of Calgary -- have only studied prolactin in female mice, not in people.
But they note that MS symptoms often ease in human pregnancy, possibly because of prolactin.
If so, prolactin could hold promise as a treatment for MS, note the researchers, who included Samuel Weiss, PhD.
"It was thought that during pregnancy, [women's] immune systems no longer destroyed the myelin," Weiss says in a Society for Neuroscience news release.
"But no previous study has tested whether pregnancy actually results in the production of new myelin, which may explain improvement of symptoms," Weiss adds.
Weiss and colleagues studied pregnant and virgin female mice with damage to their myelin.
They found that pregnant mice had both more prolactin and myelin-producing cells than the virgin mice.
The pregnant mice also did better at repairing their myelin damage than the virgin mice, the study shows.
Next, the scientists injected prolactin into virgin mice. Afterwards, the virgin mice boosted their number of myelin-producing cells and improved their ability to repair myelin damage.
If the findings are confirmed in further studies, prolactin may prove useful in treating MS, note Weiss and colleagues.
However, they suggest that since prolactin can increase inflammation, it might need to be combined with anti-inflammatory medicine.
The study appears in The Journal of Neuroscience.