Prolactin
Prolactin is polypeptide hormone of 198 amino acids with 3 disulfide bonds.
Prolactin is secreted by the lactotrophe cells of the anterior pituitary, also by other organs placenta, uterus at the end of the cycle and at the beginning of pregnancy, but also by activated leukocytes and fibroblasts. The plasma concentration of prolactin is high at birth, then decreases, increases at puberty (especially in girls) and during pregnancy. After labor, if the mother does not nurse, its concentration falls, because it is the stimulation of the nipple which maintains its secretion at a high level.
The effects of prolactin are complex. Its physiological role, which seems negligible in the maintenance of pregnancy, is to prepare breasts for feeding. In addition, prolactin inhibits the secretion of gonadotrophins.
Prolactin hypersecretion, as observed during certain tumors, induces galactorrhea, amenorrhea, anovulation, sterility or erectile dysfunction and could be implicated in autoimmune diseases.
Several drugs modify the secretion of prolactin.
- Prolactin secretion is inhibited by dopamine and dopaminomimetic agents and is decreased by the adminisration of L-dopa, bromocriptine, lisuride or quinagolide. In addition to their use for the treatment of Parkinson's disease, these D2 receptor agonists, are used in endocrinology to inhibit prolactin secretion when it is excessive and causes manifestations, for example amenorrhea-galactorrhea syndrome, sterility in women, gynecomastia and erectile dysfunctions in men…
They are also used to inhibit lactation. The prescription of bromocriptine in this indication was critized because of its possible cardiovascular adverse effects. Lisuride is also be used in this indication.
- Prolactin secretion is increased by antidopaminergic drugs such as neuroleptics, which can induce gynecomastia, galactorrhea, sterility, etc It is also increased by TRH (thyrotropin releasing hormone) and by opioid derivatives and; this could explain the amenorrhea observed in sportswomen via an increased secretion of endogenous opioids. A hyperprolactinemia must always be suspected to be caused by a drug.
Prolactin is not used in therapeutics.
|
