Development of the motor activity of the rat gastrointestinal tract by in vitro measurement.

To clarify the postnatal developmental changes of the motor activity of the gastrointestinal tract, the frequency and amplitude of spontaneous intraluminal pressure of the isolated stomach, duodenum, jejunum, and ileum of the 1- to 5-week-old rat and adult (over 12 weeks old) were examined in vitro. The spectral frequencies of the spontaneous motor activity of 1- to 2-week-old rat were significantly lower than those of the adult. They became similar to the values of the adult at 3-4 weeks after birth. The amplitudes of spontaneous motor activity of 1- to 3-week-old rats were significantly smaller than those of adults. They became similar to the values of adults at 4 weeks after birth. Body weight, stomach wet weight and the length of the total intestine increased gradually and they were still below the values of the adult even at 5 weeks after birth. The stomach was filled with just milk until the end of 2 weeks. However, by the end of 3-4 weeks, milk and solid food were found in the stomach. By the end of 5 weeks, just solid food was seen in the stomach. Therefore, the motor activity of the gastrointestinal tract at birth seems immature and gradually develops postnatally. It seems to be mature by the end of 3-4 weeks after birth. Interestingly, the time of the pacemaker or motor maturity of the gastrointestinal tract according to spontaneous frequency or pacemaker activity and amplitude seemed almost consistent with the weaning time.