PRL a single-chain peptide hormone.

Prolactin is secreted and synthesized by Lactotrophs that initiates milk production together with other hormones in the mammary gland. Prolactin by itself has a weak effect. It is considered a stress hormone it possess vital functions necessarily related to reproduction.

"Prolactin is structurally related to growth hormone and human placental lactogen.. It is unique among the anterior pituitary hormones because its major mode of hypothalamic regulation is tonic inhibition rather than intermittent stimulation." - Clinical Chemistry; Bishop et.al

Prolactin secretion is regulated by the hypothalamus which secretes both the inhibitory and excitatory hormone. Neuroendocrine neurons in the hypothalamus regulates pituitary prolactin secretion. Dopamine is a nuerotransmitter which is the major prolactin-inhibiting hormone inhibit the release of prolactin from the anterior lobe of the pituitary. Thyroid-releasing hormone, gonadotropin-releasing hormone and vasoactive intestinal polypeptide positively regulate prolactin secretion which has stimulatory effect on prolactin release.



photo source:

http://neurosurgery.ucla.edu/images/Pituitary%20Program/Prolactin.jpg

"Only after the mammary gland have been primed by estrogens, progesterones, glucocorticoids, human growth hormone, thyroxine and insulin, which exert permissive effects, does prolactin bring about milk secretion. Ejection of milk from mammary glands depends on the hormone oxytocin, which is released from the posterior pituitary. Together, milk secretion and ejection constitute lactation." - Principles of Anatomy and Physiology; 12th edition; Tortora et.al



Precautionary measures before the prolactin test. (as the patient):

1. Fasting hours as instructed by your health professional before having a prolactin test.
   
   
2. A blood prolactin determination is usually done about 2-3 hours after you wake up, sometime between 8 a.m. and 10 a.m.
   
   
3. Avoid emotional stress or strenuous exercise just before the test
   
   
4. Avoid nipple stimulation for 24 hours prior to prolactin testing.
   
   

Procedure of the test:

The health professional drawing blood will:

1. Apply tourniquet or an elastic band around your upper arm to make the veins below the band larger so it is easier to put a needle into the vein.
   
   
2. Sterilize the needle and the puncture site (most commonly with the use of alcohol)
   
   
3. Insert the needle into the vein. More than one needle stick may be needed.
   
   
4. Hook a tube to the needle to fill it with blood.
   
   
5. Release the band or tourniquet.
   
   
6. Put a sterile gauze pad or cotton ball over the needle site as the needle is removed.
7. Apply pressure to the site of puncture and then a bandage.
   
   

Reference values:

Normal values may vary in many different laboratories:

Pregnant Women: 20 to 400 ng/mL or 20 to 400 mcg/L (SI units)
Non-pregnant women: Less than 25 nanograms per milliliter (ng/mL) or 25 mcg/L (SI units)
Men: Less than 20 ng/mL or 20 mcg/L (SI units)

External and Internal Factors affecting the Tests:

1. Doing heavy and strenuous exercise before prolactin test may cause variation of the results.
   
   
2. Suffering a lot of emotional stress
   
   
3. Suffering from sleep disorders, prolactin levels are highest during sleep so if you do not sleep well, your levels may be lower than normal.
   
   
4. Nipples stimulation.
   
   
5. Taking certain medicines or even medicines for mental illness, such as phenothiazines.
   
   
   
6. Use of cocaine.

We can measure prolactin hormone level in the laboratory to asses the cause of abnormal nipple discharge, amenorrhea which is known as the absence of menstrual period in women or if a woman is infertile. In a man we test for the prolactin hormone level to detect when a pituitary gland problem is suspected. Also, a prolactin test may be done to check levels if a man lacks sexual desire or suffering erectile dysfunction. Prolactin levels may be checked when a man's testosterone levels are really low. Prolactin test is also done to see prolactinoma, a pituitary tumor that directly secretes prolactin and represents the most common type of pituitary tumor.

Hyperprolactinemia may be due to many cause such as physiologic, pathologic or even pharmacologic. Substantial increase in prolactin levels is obtaining more than 200 ng/ml indicates presence of prolactinoma. The higher the prolactin level, the more likely a pituitary gland tumor is present. Tumor size in prolactinoma is correlated in the degreee in increase in level of prolactin. Modest increase in the prolactin levels such as obtaining 25 to 100 ng/ml may be due to other medical conditions such as use of dopaminergic antagonist medication.


References:

Electronic references:

http://www.labtestsonline.org/understanding/analytes/prolactin/test.html

http://www.medic8.com/healthguide/articles/prolactin.html

http://www.vivo.colostate.edu/hbooks/pathphys/endocrine/hypopit/prolactin.html

http://www.webmd.com/a-to-z-guides/prolactin-15129?page=2

Book references:
Clinical Chemistry; Bishop et.al
Principles of Anatomy and Physiology 12th edition Tortora et.al