Prolactin: the bright and the dark side

Abstract

Prolactin is a phylogenetically old signaling molecule whose gene can be traced to lampreys more than 500 million years ago. This fact poses the question of aprimitive function for prolactin, which would explain its retention during premammalian evolution. With the origin of mammals, prolactin became linked inextricably to the development of the mammary gland and lactation.