Prolactin (PRL) is one of several polypeptide factors known to exert trophic effects on the prostate. Prolactin is currently viewed as a hormone of pituitary origin, whose production (i.e. serum levels) is controlled by dopamine. Prolactin is closely related to growth hormone. It is secreted by so-called lactotrophs in the anterior pituitary. It is also synthesized and secreted by a broad range of other cells in the body, most prominently various immune cells, the brain and the decidua of the pregnant uterus.
In women the major action of prolactin is to initiate and sustain lactation (producing milk). It occurs through a process known as lactogenesis and works along with the hormone oxytocin, which is a neurotransmitter in the brain that has not been studied extensively. Prolactin lowers levels of sex hormones (estrogen and testosterone) in both men and women. Too much prolactin and the resulting drop in estrogen or testosterone can lead to sexual and menstrual dysfunction.
Men with hyperprolactinemia (too much prolactin in the blood) typically show hypogonadism (low serum testosterone), with decreased sex drive, decreased sperm production and impotence. Many drugs, including antipsychotic agents, can cause impotency problems, often associated with excessive prolactin release. Although prolactin is known as a survival factor that supports tumor growth and confers chemoresistance in both breast and prostate cancers
Breast and prostate cancer have many parallels, including a similar lifetime risk, responsiveness to hormones, and a similar disease progression pathway. The prolactin signaling cascade is initiated upon binding of prolactin to its dimerized membrane receptor. This triggers a series of molecular events which culminate in the proliferation, anti-apoptosis, and/or chemoresistance of breast or prostate cancer cells.
Prolactin can alter cell morphology and increase DNA synthesis in prostate cells. Stat5 is the main signaling pathway triggered by prolactin, a growth factor whose local production is also increased in high-grade prostate cancers. Unlike the breast, Stat5 is constitutively active in prostate cancer and activation of Stat5 predicts earlier prostate cancer recurrence. Stat5 promotes metastatic behavior of prostate cancer cells.
Blocking prolactin release or at least partial release is necessary for patients with breast cancer and prostate cancer. Dopamine serves as the major prolactin-inhibiting factor or brake on prolactin secretion. Dopamine is secreted into portal blood by hypothalamic neurons, binds to receptors on lactotrophs, and inhibits both the synthesis and secretion of prolactin.
Estrogens are known to cause hyperprolactinemia, most probably by acting on the tuberoinfundibular dopaminergic (TIDA) system. Therefore, to stimulate prolactin secretion, estrogens inhibit TIDA neurons to decrease dopamine production. Dopamine neurons are well known to enhance libido and sexual performance. One of the roles of dopamine D2 receptor agonists or activators is to block prolactin secretion. Agents and drugs that interfere with dopamine secretion or receptor binding lead to enhanced secretion of prolactin.
Chaste tree (Vitex agnus-castus) herb contains several different constituents, including flavonoids, iridoid glycosides, and terpenoids. It has been used since ancient Greek times and has been shown clinically to be effective for the treatment of premenstrual syndrome (PMS). Chaste berry does not contain hormones. Currently, the fruit extract is used as a dietary supplement for estrogen hormone imbalance which can produce menstrual cycle disorders and PMS. Some men use chaste tree berries for increasing the flow of urine, for treating benign prostatic hyperplasia (BPH)
Chaste berry extracts have been shown to exhibit antitumor activities in different human cancer cell lines, including prostate cancer. Chaste tree berries contain compounds that directly activate dopamine D2 receptors. These receptors are well known to activate neurological pathways. These pathways also inhibit the release of prolactin from the pituitary gland at the base of the brain. It is clear that excessive prolactin secretion plays a role in prostate cancer. Chaste berry extracts act on the dopamine D2 receptor to block this affect. ProstaZym contains the purest, most highly bioavailable chaste berry extracts. It is possible to modulate the prolactin response.