No effect of prostaglandin synthesis inhibition on muscle reflexes in fetal lambs.

The effects of inhibiting prostaglandin (PG) synthesis on fetal breathing movements and on the amplitude of reflex contraction of the digastric muscle (five trials) or hindlimb semitendinosus muscle (seven trials) has been studied in six fetal lambs at 123-139 days gestation. Infusion of either indomethacin (100 mg) or acetaminophen (300 mg) in 30 ml saline over 30 min resulted in an increase in the amplitude and incidence of breathing movements for 3-18 h in the different trials, but there was no change in the mean amplitude of either reflex or in the normal variation of reflex amplitude with changes in electrocortical activity. It is concluded that PGs modulate fetal breathing movements by an action on the brain stem chemoreceptors but do not alter the excitability of neural pathways subserving some cranial and spinal reflexes.