Placental transfer of central nervous system depressants in sheep.

Continuous monitoring of the foetal electrocorticogram, eye movements and heart rate in ewes during the last month of gestation showed rapid placental transfer from the mother to the foetus of phenothiazine derivatives (acepromazine maleate), short-acting barbiturates (thiopental sodium) and narcotic analgesics (meperidine). Acepromazine and thiopental partially disrupted the foetal sleep cycle by synchronization of the ECoG for 1-2 h but increased the heart rate for 2-3 h. The effects of meperidine were similar but lasted only 5-10 min for the ECoG and less than 0.5 h for the heart rate.