The effects of pentobarbitone and pethidine on foetal breathing movements in sheep.

1 Small doses of pentobarbitone (4 mg/kg i.v.) administered to sheep in the last third of pregancy had little overt effect on the mothers. In the foetus they caused arrest of breathing movements, an alteration in the character of the electrocorticogram and cardiovascular changes which varied with gestational age. 2 In contrast, relatively large doses of pethidine (100-200 mg) admininstered to the mother had no consistent effect on normal foetal breathing movements, though they abolished the foetal response to hypercapnia. 3 The results are discussed in relation to feotal sleep state.