Effects of oxytocin treatment early in pregnancy on fetal growth in ad libitum-fed and food-restricted rats

The effects of oxytocin on fetal and placental growth and on maternal weigh t gain and accumulation of body fat were studied in ad libitum-fed and food -restricted (receiving 70% of the food intake of the ad libitum-fed group) pregnant rats. Further, a possible role of the IGF axis in mediating oxytoc in-induced changes was assessed. Pregnant rats were injected subcutaneously once a day during gestational d 1-5 with saline or oxytocin (1 mg/kg;). Ad libitum-fed oxytocin-treated pregnant rats had higher circulating levels o f IGF-I, larger placentas, fetuses, and newborn pups and contained less bod y fat at the end of pregnancy. In food-restricted darns, oxytocin-treatment had no effect on fetal and placental growth. Additionally, food restrictio n attenuated the normal increase in IGF binding protein-3 protease proteoly sis during pregnancy. The results show that oxytocin may affect maternal ad aptations to pregnancy and stimulate fetal growth. We suggest that this eff ect may be mediated by increased IGF-I in ad libitum-fed animals, whereas f ood restriction may block this effect by resulting in low levels of circula ting IGF-I and by attenuating the pregnancy-associated increase in IGF bind ing protein-3 protease activity and, thereby, further compromise IGF bioava ilability.