Prolactin (PRL or PRL1), chorionic somatomammotropin, and related pituitary gland hormones
Prolactin is primarily responsible for stimulating milk production and breast development in mammals. Aside from roles in reproduction, various functions have been attributed to prolactin, more than for other pituitary gland hormones combined. These are roles in growth and development, metamorphosis, metabolism of lipids, carbohydrates, and steroids, brain biochemistry and even immunoregulation, among others. Most of these roles are poorly understood, but it has become clear that many prolactin-like hormones are actually produced in the placenta and not the pituitary.
Jiyao W et al.(2023). "The conserved domain database in 2023.",