Structure and properties
Prolactin is a hormone composed of 198 amino acids that is closely related chemically to somatotropin.
Synthesis and release
Prolactin synthesis occurs primarily in the cells of the anterior pituitary. In addition, prolactin is also produced in the placenta, mammary glands, certain neurons, and T lymphocytes. Prolactin exhibits circadian rhythms in both sexes with maximal levels during non-rapid-eye-movement (NREM) sleep. Episodically, prolactin is released approximately every 90 minutes. During pregnancy and lactation, prolactin concentrations are elevated. Prolactin is also released during orgasm. TRH and neural stimuli stimulate its release. Dopamine and dopamine agonists inhibit prolactin secretion, and dopamine antagonists promote release.
Effects
Influence on reproduction:
- During pregnancy, prolactin, along with estrogens and progesterone, promotes growth of the mammary glands. After birth, it promotes milk production.
- Influencing the relationship of the parents to the child (maternal instinct).
- Suppression of the resumption of the menstrual cycle.
- Increasing the secretion of progesterone
- Inhibition of GnRH secretion
Influence on homeostasis:
- Immune modulation: prolactin plays an important role in the regulation of humoral and cellular immune responses and autoimmune diseases.
- Osmotic balance: increase water transport across the mammary cell membrane, sodium reabsorption in the small intestine.
- Promote the formation of new blood vessels
Influencing the central nervous system:
- Activation of dopaminergic neurons to regulate their own secretion.
- Stimulation of appetite
- Anxiety-relieving
- Reduction of stress
- Regulation of oxytocin-producing neurons.
- Stimulation of myelination in the CNS.
Mechanism of action
Binding to transmembrane prolactin receptors.
Pathophysiology
- Hyperprolactinemia
- Prolactinoma (pituitary tumor that secretes prolactin).
Things to know
Because prolactin is also produced in the brain, it can function as a neuropeptide and as a neuroendocrine hormone. Determination of prolactin levels is indicated in menstrual disorders, corpus luteum insufficiency, galactorrhea, mild virilization symptoms, female sterility, libido and potency disorders, hypogonadism, and pituitary as well as hypothalamic disorders. During lactation, prolactin secretion is suppressed by increased plasma osmolarity. This mechanism should prevent the development of hypertonic dehydration during lactation.
