The massive surge in the maternal hormone oxytocin that occurs during delivery might help protect newborns against brain damage, a new study in rats suggests. Researchers say the findings should encourage scientists to investigate whether elective caesarean sections, which lack this oxytocin surge, disrupt normal brain development. Yehezkel Ben-Ari, a neuroscientist at the Mediterranean Institute of Neurobiology in Marseille, France, and colleagues compared brain tissue samples from rat pups born naturally or by caesarean section. Brain cells from the naturally born pups did not fire in response to the nerve signalling chemical GABA, the researchers found. By comparison, at least 50% of the sampled cells from rats delivered by caesareans responded to the GABA signals.
When the team gave pregnant rats atosiban – a drug that specifically blocks oxytocin’s effects – the brain cells from these rats were easily excited by GABA. This revealed that oxytocin was the hormone that made neurons from naturally delivered pups less receptive to GABA. Oxytocin levels surge dramatically during labour – partly due to the pressure exerted by the baby’s head on the cervix – along with other hormones such as prostaglandins. Ben-Ari believes that by “quieting” cells, oxytocin may prevent brain damage due to oxygen deprivation that can occur during labour. In fact, they found that the brain cells of rat pups delivered naturally lived for an hour when placed in a solution that lacked oxygen. Brain cells from pups with a mother whose oxytocin was blocked by atosiban lived only 40 minutes.
By making cells less responsive, oxytocin reduces the oxygen they require for energy production, the team says. The hormone could provide a natural, temporary safety net to avoid damage from lengthy or difficult deliveries, says Ben-Ari. “It’s like putting a television in standby mode to reduce energy consumption,” explains team member Rustem Khazipov. Intense exposure to oxytocin during natural delivery might also encourage brain cell maturation, says Ben-Ari. He wonders if babies born by elective caesarean section miss out. “I think the oxytocin and other hormones the mother is providing are important – we should not ignore them,” he says. In many places the rate of caesarean deliveries is going up. According to the US National Institutes of Health, the rate has increased 40% over the last decade and now accounts for three deliveries in every 10. This is partly due to a rise in the number of women having elective caesareans, rather than for emergency delivery purposes.
“This is exactly the kind of study that gives me pause,” says Carol Sakala, director of programs at the New York-based Childbirth Connection, a maternity care advocacy group. “We have grave concerns about the trend for caesareans,” says Sakala. “Instead of going full-steam ahead, shouldn’t we be calling on the precautionary principle?” But others say it is too soon to view these findings as reason to avoid c-sections wherever possible. “It is premature to translate these findings into clinical practice for women,” says Cynthia Chazotte at the Albert Einstein College of Medicine in New York. “While the fetuses delivered by elective caesarean will not have the protective effect of oxytocin, they presumably will not be at the same risk for [oxygen deprivation] as fetuses exposed to the stresses of labour,” says Ashley Roman at the New York University School of Medicine. “I don’t think that these results can be used to counsel patients against elective caesarean delivery,” she adds.
January 9, 2007
Original web page at New Scientist