Inhibition of breathing movements in fetal sheep by prostaglandins.

We studied the effects of infusions (duration 13.4 +/- 2.9 h) of prostaglandins (PG) on fetal breathing movements (FBM) in 12 fetal sheep at 122-141 days gestation. We gave similar doses (1.1 +/- 0.7 microgram . kg-1 . min-1) of PGE2 (8 studies), PGF2 alpha (5 studies), and cyclic endoperoxide analogues (6 studies). During control periods (304 h), incidence of FBM was 41%; this decreased during every infusion. With PGE2, incidence of FBM markedly decreased to 9.8% of control (P less than 0.001). With the other agents the decrease was less profound; incidence of FBM with PGF2 alpha was 63.7% of control and with endoperoxide analogues 69.4% of control (P less than 0.05 for both). During infusions there were no changes in fetal heart rate, arterial blood pressure, pH, or blood gas tensions. In three fetuses (5 infusions) with electrocorticogram recordings, incidence of low-voltage fast activity was unchanged from control values. Inhibition of FBM by PGE2, combined with previous results showing stimulation of FBM by PG synthetase inhibitors, suggests that endogenous PG may inhibit breathing movements in utero and that a change in PG metabolism may contribute to the change in control of breathing at birth.