The Origin of Prolactin, Its Relationship with HGH, and Its Central Role
Prolactin is a hormone crucial for reproduction that primarily promotes lactation, but it is also important for non-pregnant women and men.
This is a protein hormone secreted from the anterior pituitary gland and belongs to the somatotropin family along with human growth hormone (HGH); this family also includes hormones like chorionic somatomammotropin (lactogen).
HGH and prolactin have similar structures and amino acid sequences, suggesting they evolutionarily derived from a common ancestor.
In 1928, researchers discovered that pituitary extracts stimulated milk secretion in rabbits, and lactation requires a combination of several hormones, including estrogen, prolactin, and progesterone.
Prolactin acts on protoplasmic receptors in the mammary alveoli, while estrogen promotes the proliferation of prolactin receptors, and progesterone inhibits it.
Additionally, estrogen stimulates prolactin secretion from the pituitary gland, and during pregnancy, prolactin production surges.
Estrogen infusion directly activates prolactin gene transcription, thereby increasing its synthesis.
The Role, Effects, and Side Effects of Prolactin in Men
Besides promoting lactation, prolactin can also affect testicular function.
In rat experiments, the inhibition of pituitary prolactin secretion was associated with a decrease in testicular LH receptors, suggesting that prolactin is essential for maintaining LH receptors.
However, excessive prolactin can cause hypogonadism, so maintaining an appropriate level is important.
Prolactin increases the number of LH receptors and acts as a mild gonadotropin, but it inhibits GnRH secretion.
In men, prolactin affects libido and orgasm, with levels increasing after orgasm to regulate the refractory period.
Antagonistic substances like dopamine can increase orgasm intensity and shorten the refractory period.
Conversely, chronically elevated prolactin can lead to decreased libido and orgasmic dysfunction.
In cases of hyperprolactinemia, side effects such as nipple lactation can occur; this phenomenon is generally mild and happens upon physical stimulation.
In some cases, the nipples and surrounding tissue may swell, and in severe instances, it can be accompanied by gynecomastia.
Normal Physiological Range of Prolactin
Like other hormones, prolactin is necessary for the body, so there is an ideal range in which it should be present.
Just as prolactin levels should not be too high, they should not be too low either.
Below are general indicators representing the levels an individual should ideally maintain after a blood test.
Generally, men should be in the 5-15 µg/L range.
Non-pregnant women should be in the 5-25 µg/L range, while pregnant women should be in the 35-385 µg/L range.
