Clinical Significance

PRL is a protein hormone secreted by the pituitary gland and is composed of 199 amino acid residues. Its effect on mammary gland and lactation is mainly to promote mammary gland development and growth, and to cause and maintain lactation. 

During puberty, mammary gland development is mainly stimulated by estrogen, while progesterone and growth hormone also play a synergistic role. During pregnancy, prolactin, human chorionic growth hormone, progesterone and estrogen cause further development of breast tissue.

Prolactin loses its effectiveness due to high concentrations of estrogen and progesterone in the blood, which compete with prolactin for mammary cell receptors. After delivery, the concentration of progesterone and estrogen in the blood decreases, and prolactin plays a role in initiating and maintaining lactation. The fetal pituitary gland is capable of secreting, storing and releasing prolactin. Its concentration in the blood peaks in the weeks before delivery. Its concentration in amniotic fluid is also 5 to 10 times higher than in maternal serum.