Yes , breastfeeding stimulates the pituitary gland to release  the hormone oxytocin, This hormones primary acts to contract the smooth muscles  such as sacs of milk in your breast. Contraction of the breast causes your milk to move to the front of the breast making it available for your baby. With each feeding, the hormone oxytocin causes the smooth muscles in the uterus to contract, enabling  it  to get to its pre-pregnancy size.

Oxytocin has one other important effect . They induce a  loving feeling in the mom towards the baby. This is why it is called the love hormone.