Final answer:
Dopamine serves as the prolactin inhibiting factor to regulate prolactin levels by inhibiting its release from the anterior pituitary gland, thus controlling milk production in females, especially outside of pregnancy when milk production is not necessary.
Step-by-step explanation:
The function of the prolactin inhibiting factor, which is now known to be dopamine, is to inhibit the release of prolactin from the anterior pituitary gland. Prolactin is a hormone essential for the production of milk in the mammary glands following childbirth. The hypothalamus produces dopamine, acting as the prolactin-inhibiting hormone (PIH), to maintain prolactin levels at a balance so that milk production is regulated appropriately. It counteracts the function of prolactin-releasing hormone (PRH), which stimulates the release of prolactin. In non-pregnant females, dopamine keeps prolactin secretion in check, preventing unnecessary lactation. During pregnancy, PRH levels increase, leading to a rise in prolactin and subsequent milk production.