Prolactin is secreted from the pituitary gland in response to eating, mating, estrogen treatment, ovulation, and nursing. Prolactin is secreted in a pulsatile fashion in between these events.Prolactin also plays an essential role in metabolism, regulation of the immune system, and pancreatic development.here is a diurnal as well as an ovulatory cycle in prolactin secretion. In many mammals, there is also a seasonal change in prolactin release. During pregnancy, high circulating concentrations of estrogen and progesterone increase prolactin levels by 10- to 20-fold.