Prolactin | You and Your Hormones from the Society for Endocrinology
J Endocrinol Invest. Sep;18(8) Relationship between beta- estradiol and prolactin in the regulation of natural killer cell activity during. The ovarian secretion of estradiol, androstenedione, testosterone, and progesterone and the concentration of LH, FSH, and prolactin were measured. During pregnancy, prolactin secretion increases and stimulates growth of the breast, but high estrogen and progesterone secretion prevent milk production.
Hyperprolactinemia Prolactin Regulation Prolactin is the hormone that stimulates milk production in the breast. During pregnancy, prolactin secretion increases and stimulates growth of the breast, but high estrogen and progesterone secretion prevent milk production. After delivery, estrogen and progesterone levels drop, and prolactin stimulates the production of milk by alveolar cells in the breast.
Figure 1 illustrates how bursts of prolactin secretion are stimulated so as to maintain milk production during lactation. Suckling by the infant stimulates nipple mechanoreceptors that are connected by neural circuits to two types of neurosecretory cells in the hypothalamus. One type of neurosecretory cell is a magnocellular cell that releases the hormone oxytocin from the posterior pituitary.
Role of estrogen in the dopaminergic control of prolactin secretion.
These cells are stimulated by suckling. Oxytocin causes milk ejection, in which smooth muscle-like cells called myoepithelial cells contract to push the milk from the glands into the breast ducts so that the infant can easily suck it out. The other neurosecretory cell is a parvocellular cell that releases dopamine at the median eminence. Dopamine acts as a hormone, traveling to the anterior pituitary via the hypophyseal portal vessels to inhibit prolactin secretion by anterior pituitary cells.
Suckling, via neural connections inhibits dopamine secretion, thereby removing inhibition to allow increased prolactin secretion and stimulation of milk production in the breast.
- Role of estrogen in the dopaminergic control of prolactin secretion.
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- You and Your Hormones
Causes and Treatments Hyperprolactinemia is most often caused by a prolactinoma, a common type of pituitary tumor that hypersecretes prolactin. Hyperprolactinemia high prolactin secretion causes infertility because prolactin inhibits GnRH secretion. Thus, hyperprolactinemia is an example of the type of infertility called hypogonadotropic hypogonadism, where low gonadal function results from low gonadotropin secretion.
Drugs that mimic the action of dopamine are therefore useful in treating patients with high serum prolactin concentrations.Pregnancy hormones - Hormones during pregnancy
Prolactin-stimulating factors also exist, and included among them are GnRH, thyrotropin-releasing hormoneand vasoactive intestinal polypeptide. However, the physiologic importance of these prolactin-stimulating factors is not well-defined. One example of a prolactin-stimulating factor for which a role has been identified is estrogenwhich stimulates prolactin synthesis and secretion in the late stages of pregnancy to prepare the mammary glands for lactation.
Prolactin deficiency and excess Prolactin deficiency occurs as a result of general pituitary hormone deficiency, which is characterized by the deficiency of other pituitary hormones in addition to prolactin. A primary cause of pituitary hormone deficiency is a pituitary tumour. The most striking example of prolactin deficiency is that of Sheehan syndromein which the anterior pituitary gland of pregnant women is partly or totally destroyed during or shortly after giving birth.
This syndrome tends to occur more frequently in women who have excessive bleeding during delivery.
Affected women do not produce breast milk and cannot nurse their infants. Prolactin deficiency does not cause abnormalities in women who are not trying to nurse their infants and does not cause abnormalities in men.
Increased prolactin secretion can be caused by damage to the pituitary stalk, thereby interrupting the flow of dopamine from the hypothalamus through the hypophyseal-portal circulation to the lactotrophs. In addition, increased prolactin secretion may be caused by prolactin-producing pituitary tumours, such as lactotroph adenomas or prolactinomas, and by several systemic diseases, notably thyroid deficiency.
Many drugs, particularly those used for the treatment of psychological or psychiatric disorders, high blood pressure hypertensionand pain may also increase prolactin secretion.
In some patients with high serum prolactin concentrations hyperprolactinemiahowever, no cause is discernible, and they are said to have idiopathic hyperprolactinemia. In women of reproductive age, high serum prolactin concentrations result in decreased secretion of gonadotropins and therefore decreased cyclic ovarian function.
The frequency of menstrual cycles decreases oligomenorrheaand the cycle may even cease amenorrhea altogether. Symptoms of estrogen deficiency, such as loss of sexual desire, dryness of the vaginainfertilityand, less often, abnormal lactation galactorrhea also occur.
High serum prolactin concentrations are not usually associated with any symptoms in postmenopausal women, although in very rare cases galactorrhea may occur. In men, high serum prolactin concentrations also decrease gonadotropin secretion but therefore decrease testicular function, resulting in low serum testosterone concentrations.
The major symptoms are loss of sexual desire, erectile dysfunctionmuscle weakness, and infertility.
Prolactinomas are the most common type of hormone-secreting pituitary tumour. They are four to five times more common in women than in men. However, prolactinomas tend to be larger in men at the time of diagnosis.