Prolactin

INTRODUCTION:

• Prolactin is a hormone that plays a role in fertility by inhibiting FSH and GnRH the hormones that trigger ovulation and allow eggs to develop and mature.
• Also called luteotropic hormone (LTH) or luteotropin, a protein hormone produced by the pituitary gland of mammals that acts with other hormones to initiate secretion of milk by the mammary glands. 

PHYSIOLOGY:

• In breast-feeding mothers, tactile stimulation of the nipples and the breast by the suckling infant blocks the secretion of hypothalamic dopamine (which normally inhibits prolactin)
• This results in a sharp rise in serum prolactin concentrations
• High serum prolactin concentrations inhibit secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus,
• Decreasing the secretion of gonadotropins(luteinizing hormone and follicle-stimulating hormone), and may also inhibit the action of gonadotropins on the gonads.
• Thus, high serum prolactin concentrations during lactation reduce fertility, protecting lactating women from a premature pregnancy.
• Prolactin acts to maintain the corpus luteum of the ovary & thus helps to sustain pregnancy. 
• The secretion of prolactin is stimulated by 
• High doses of estrogens
• Stress and exercise. 
• Pregnancy
• Increased FSH
• Increased libido
• Increased testosterone
• Sleep 

REGULATION OF SECRETION:

• Hypothalamic control of prolactin secretion is primarily inhibitory.
• Factor that inhibits prolactin secretion is dopamine
• Drugs that mimic the action of dopamine are therefore useful in treating patients with high serum prolactin concentrations.
• Prolactin-stimulating factors : GnRH, TRH, and VIP.
• Estrogen, which stimulates prolactin synthesis and secretion in the late stages of pregnancy to prepare the mammary glands for lactation.

PROLACTIN DEFICIENCY  & EXCESS:

General pituitary hormone deficiency

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Prolactin deficiency

CAUSES:

• Pituitary tumour
• Sheehan syndrome:Anterior pituitary gland of pregnant women is partly or totally destroyed during or shortly after giving birth. 

Increased prolactin secretion

CAUSES:

• Damage to pituitary stalk→ interrupting flow of dopamine from the hypothalamus to the lactotrophs.
• Prolactin-producing pituitary tumours:Lactotroph adenomas or prolactinomas
• Thyroid deficiency.
• Drugs:
• Psychological or psychiatric disorders
• Antihypertensive, and pain 
• Metoclopramide: Hyperprolactinemia 

EFFECTS:

In women of reproductive age:

• Decreased secretion of gonadotropins and therefore decreased cyclic ovarian function.
• Oligomenorrhea
• Amenorrhea

Symptoms of estrogen deficiency

• Loss of sexual desire
• Dryness of the vagina
• Infertility
• Galactorrhea 

In postmenopausal women:Galactorrhea

In men:

• Decrease testicular function, resulting in low serum testosterone concentrations. 
• Loss of sexual desire, erectile dysfunction, muscle weakness, and infertility.

Prolactinomas :

• Most common type of hormone-secreting pituitary tumour.
• Four to five times more common in women than in men.
• Larger in men at the time of diagnosis.
• Symptoms:
• Rarely symptomatic
• Headaches
• Disturbances in vision
• Symptoms and signs of other pituitary hormone deficiencies.
• Treated with drugs :Bromocriptine and cabergoline. 
• Surgery or radiation therapy. 
• Patients with few symptoms may not require treatment. 
• These patients tend to have tumours that do not grow and tend to have mild hyperprolactinemia that does not increase.