['Progesterone, estrogen and the hormonal complex of pregnancy have been responsible for some degree of colon hypomotility in human pregnancy.', 'To find out if estrogen, progesterone and the hormonal complex of pregnancy decrease colon myoelectric activity.', 'The study was performed in 37 healthy female rats in which electrodes were implanted on the serosa of the proximal ascendent, distal ascendent, transverse, and descendent colon. We analyzed the records of colon myoelectric activity in vivo in five groups: control, ovariectomized, ovariectomized and treated with estrogen, ovariectomized and treated with progesterone, and pregnant rats.', 'We found a great variation in myoelectric activity in all groups studied. The mean of electric activity did not show statistical difference among the five groups, but pregnant rats had a statistically significant higher duration of maximum electric activity in all distances from the cecocolon junction.'] Do progesterone , estrogen and pregnancy decrease colon myoelectric activity in rats : an in vivo study?