Early exposure to oxytocin affects the age of vaginal opening and first estrus in female rats.

Neonatal exposure to exogenous oxytocin (OT) can have long-term effects on the subsequent expression of adult behavior and physiology. Here, we test the prediction that early postnatal exposure to OT can affect the timing of sexual maturation in females, as indicated by the age of vaginal opening and the onset of first estrus. To test this hypothesis, female Sprague-Dawley rats received one of four treatments beginning on the day of birth and continuing for the next 6 days. Three groups received an intraperitoneal injection of one of the following: OT (1 mug/g), an OT antagonist (OTA, 0.1 mug/g) or isotonic saline (vehicle control). The fourth group was handled but not injected. Females were then examined to determine the day of vaginal opening and first estrus. The potential effects of OT on body weight were also measured, with females being weighed on postnatal days 1-7, 70, 91 and 136. Treatment with OT significantly delayed the age of vaginal opening and the onset of first estrus. There was no effect on weight. Results indicate that early exposure to OT can affect the timing and development of female sexual maturation.