Increased fetal breathing activity after fetal hypophysectomy.

Continuous recordings of tracheal pressure were made from seven control fetal sheep and seven in which hypophysectomy was attempted. Hypophysectomy was partial or complete in five fetuses, and in two the forebrain and brain stem were destroyed accidentally. The incidence of rapid, irregular breathing movements decreased in the control fetuses before spontaneous parturition. No fetal breathing movements were recorded from the two fetuses in which the forebrain and brain stem were destroyed. The incidence of fetal breathing movements (38.1 +/- 0.9 minutes per hour) was significantly greater in the fetuses after electrocoagulation of the fetal pituitary than in the control fetuses (24.5 +/- 1.7 min/hour, p less than 0.001). This was due to an increase in the incidence of rapid, irregular breathing movements and to intermittent, prolonged periods (more than 3 hours duration) of fetal breathing movements. The longest period of continuous fetal breathing recorded was 52 hours. There were two alternating patterns of breathing in these prolonged periods of fetal breathing movements. In one pattern, the breathing movements were irregular in rate and depth and resembled the episodes of breathing movements which occurred in the control fetuses. The other pattern consisted of breathing movements which were regular in rate and depth but among which were interspersed a few single deeper breaths. This pattern is similar to that reported previously for the lamb during quiet sleep after birth.