Chronic oxytocin treatment during late gestation and lactation impairs development of rat offspring.

The nonapeptide oxytocin (OT) plays an important role in timing and course of parturition, and in milk ejection during lactation. Exogenously enhanced OT levels were reported to impair body development of rat offspring at birth and during postnatal stages. In the present study, this effect was further investigated by giving pregnant rats of postcoital day 17 a SC implant that delivers small amounts of OT for 2 months (approximately threefold enhancement of OT levels), and by introducing a crossfostering protocol for the offspring. A slightly reduced body weight of 5 to 7% was again observed in pups born to OT-implanted dams. When reared postnatally by OT-treated mothers, pups lost weight gain (-7 to -10%). During the weaning period, however, body size caught up with that of control animals. When nursed by an untreated mother, this recovery took place before that period. Growth of control offspring was also hampered when placed with OT-treated mothers, but these pups failed to recover from low body weights which lasted up to at least 70 days of age (-7%). Daily urine production of the pups born of and reared by the OT-treated mothers was reduced at 1 month of age, but this effect was only transient and had disappeared at 70 days of age. Notwithstanding, the recovery of body growth, brain sizes, and cerebellar DNA, i.e., cell content was reduced in the pups born and reared by OT-treated mothers, indicative of a lasting effect on brain development.(ABSTRACT TRUNCATED AT 250 WORDS)