Transplacental transfer of beta-adrenergic drugs studied by an in vitro perfusion method of an isolated human placental lobule.

A study was made of the transfer across an in vitro perfused human placenta of four beta-mimetics commonly used in obstetric practice. Between 2% and 3% of fenoterol, ritodrine, and salbutamol appeared on the fetal side after bolus injection into the maternal circulation. For hexoprenaline, the transfer (1%) was significantly lower than that observed with other beta-mimetics studied. With constant infusion of fenoterol into the maternal circulation and recycling of a small volume of perfusate on the fetal side, a fairly rapid rise in the concentration was seen. Some sulfate conjugation of fenoterol during its diffusion from the maternal to the fetal side of the placenta could be seen. In the in vitro perfused human placental lobule there is no apparent effect of synthetic beta-mimetics on the transfer of antipyrine or glucose and no stimulation of the production of lactate and pyruvate.