Regulation of prolactin secretion at the pituitary level

[Physiopathological link between polycystic ovary syndrome and hyperprolactinemia: myth or reality?]

Polycystic ovary syndrome (PCOS) and hyperprolactinemia are the two most common etiologies of disorders of the cycle in women. In clinical practice, it is not unusual to find hyperprolactinemia associated with clinical, hormonal and ultrasound features of PCOS. However, currently, there is no evidence of a pathophysiological link between these two entities. Thus, this association seems to be fortuitous. Therefore, hyperprolactinemia in women with PCOS must lead to etiological investigations, including eliminating macroprolactinemia (excess of "big prolactin" and/or "big-big prolactin"). Finally, symptomatic hyperprolactinemias (excluding macroprolactinemia) can "mask" an underlying PCOS through a gonadotropic inhibition. Moreover, symptomatic hyperprolactinemias can provide clinical and ultrasound features of a "moderate" PCOS. Therefore, in agreement with the consensus of Rotterdam, PCOS must remain a diagnosis of exclusion, after eliminating symptomatic hyperprolactinemias (excluded macroprolactinemia) and all other etiologies of hyperandrogenism.

Prolactin: structure, function, and regulation of secretion

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.