Prolactin (PRL), or Luteotropic Hormone (LTH), is a protein consisting of peptide hormones, which regulate immune and endocrine functions within the human body.

Production and secretion of Prolactin

MRNA and DNA genetic structures govern how amino acids secrete peptide hormones into the blood stream for cell synthesis into the nucleus, which are then used for biological function. Prolactin is one of the peptide hormones released by the pituitary gland from the anterior, or adenohypophysis lactotrope cells, stimulating mammary glands. Prolactin is also secreted by cells in the breasts and uterine lining or endometrium (decidua).

Prolactin function

Prolactin and cytokine receptors impact immune system function through their interaction with Prolactin molecules. They are transmembrane protein receptors, which allow for intercellular communication and signal transduction for hormones, growth factors, cytokines, neurotransmitters and cell recognition. A receptor deficiency causes immunodeficiency within the body. Therefore, Prolactin function is vital to regulate healthy cell growth and differentiation, blood clotting, blood cell formation (Haematopoiesis), blood vessel growth (angiogenesis), metabolism, endocrine process, brain and behavioural function.

Pituitary Prolactin secretion

The hypothalamus region of the brain regulates pituitary Prolactin secretion through the endocrine neurons. These neurosecretory and tuberoinfundibular (TIDA) neurons inhibit Prolactin secretion through dopamine receptors and function. Dopamine and other hormones, such as estrogen, progesterone and thyrotropin, send out signals for Prolactin production and secretion throughout the human body. This secretion is further regulated by other peptides, such as vasoactive intestinal and histidine isoleucine peptides.

Prolactin function during pregnancy and childbirth

Prolactin function involves lactation, which is the stimulation of the mammary glands for breast milk production. During pregnancy these mammary glands enlarge due to Prolactin concentrations. The breast milk production, or lactogenesis, is contained through progesterone function during pregnancy (milk-ejection reflex) and only ejected for breast-feeding after birth, as the progesterone hormone levels reduce. Suckling by the infant stimulates further Prolactin release for lactation. The unborn baby is also affected by Prolactin, sometimes having milky secretion, or Witch's milk, from the nipples that soon subsides after birth.

Prolactin and infant breathing

Prolactin also plays a role in foetal lung development, allowing for surfactant molecules to diffuse and absorb at interfaces joining water and air, occurring at birth as the baby starts to breathe and use its lungs outside of the womb. After birth Prolactin levels in the baby's body deriving from the mother allow for immune tolerance and further immune system development.

Prolactin and sexual gratification

Recent research reveals that Prolactin may also play a role in sexual gratification after sexual intercourse. Dopamine is the hormone responsible for sexual drive and arousal. Prolactin levels repress dopamine's response for sexual arousal. Measures of Prolactin levels after intercourse may indicate degrees of sexual satisfaction. Libido loss, impotence and ovulatory cycle suppression in females may be identified by high levels of Prolactin.

Prolactin stimulates brain cell proliferation

Precursor cells may be multi-potent stem cells or differentiate later into organs. Prolactin functions to stimulate precursor cell proliferation, such as for oligodendrocyte precursor cells (neuroglia brain cells) for central nervous system function.

Role of Prolactin levels in diagnosis

From the functions of Prolactin you can soon deduce how useful Prolactin levels are for the diagnosis of immunodeficiency, metabolic, endocrine, lactation, sexual, vascular and blood-related medical conditions. Prolactin levels are often used to check for:

  • Normal sexual hormone function.
  • Ovarian cycle function for female fertility or poly-cystic ovarian syndrome.
  • Impotence, hypogonadism or erectile dysfunction in men.
  • Lactation for breastfeeding and galactorrhea (non-pregnancy milk production).
  • Dopamine function.
  • Epileptic versus non-epileptic seizures.
  • Hyperprolactinaemia.
  • Prolactinoma or tumour of the pituitary gland.
  • Hypothyroidism.
  • Kidney disease.
  • Medically-induced Prolactin deficiency, caused by anti-psychotic drugs.
  • Visual disturbances and headaches.
  • Eating disorders, such as bulimia and anorexia.

Different health conditions and diseases can be diagnosed based on high or low Prolactin levels. We all normally have small amounts of Prolactin levels in our blood stream.

Prolactin Testing

To test Prolactin levels for medical conditions a blood sample is drawn for testing, usually within about an hour of a person's waking to determine the type of seizure after occurrence. A doctor carries out Prolactin tests in a medical facility and no preparation is usually necessary. In certain cases Prolactin testing is combined with Magnetic Resonance Imaging (MRI) scans or other appropriate diagnostic tests.

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