Prolactin | You and Your Hormones from the Society for Endocrinology
Prolactin stimulates the production of breast milk and is necessary for normal milk What's the Difference Between a Brand-Name Drug and a Generic Dru. What can interfere with oxytocin and what can help? Oxytocin is also the hormone involved in social relationships, bonding, trust, and love. Oxytocin The hormone related to the production of breast milk is called prolactin. Prolactin (PRL), also known as luteotropic hormone or luteotropin, is a protein that is best known for its role in enabling mammals, usually females, to produce milk. It is influential in over separate processes in various vertebrates, including humans. Prolactin is secreted from the pituitary gland in response to eating, mating, . The suckling stimulus also triggers.
A number of other hormones, such as oestrogen, are involved indirectly in lactation 2. When a baby suckles at the breast, sensory impulses pass from the nipple to the brain. In response, the anterior lobe of the pituitary gland secretes prolactin and the posterior lobe secretes oxytocin. Prolactin Prolactin is necessary for the secretion of milk by the cells of the alveoli. The level of prolactin in the blood increases markedly during pregnancy, and stimulates the growth and development of the mammary tissue, in preparation for the production of milk However, milk is not secreted then, because progesterone and oestrogen, the hormones of pregnancy, block this action of prolactin.
After delivery, levels of progesterone and oestrogen fall rapidly, prolactin is no longer blocked, and milk secretion begins. When a baby suckles, the level of prolactin in the blood increases, and stimulates production of milk by the alveoli Figure 4. The prolactin level is highest about 30 minutes after the beginning of the feed, so its most important effect is to make milk for the next feed During the first few weeks, the more a baby suckles and stimulates the nipple, the more prolactin is produced, and the more milk is produced.
This effect is particularly important at the time when lactation is becoming established. Although prolactin is still necessary for milk production, after a few weeks there is not a close relationship between the amount of prolactin and the amount of milk produced.
However, if the mother stops breastfeeding, milk secretion may stop too — then the milk will dry up. More prolactin is produced at night, so breastfeeding at night is especially helpful for keeping up the milk supply. Prolactin seems to make a mother feel relaxed and sleepy, so she usually rests well even if she breastfeeds at night.
Suckling affects the release of other pituitary hormones, including gonadotrophin releasing hormone GnRHfollicle stimulating hormone, and luteinising hormone, which results in suppression of ovulation and menstruation. Therefore, frequent breastfeeding can help to delay a new pregnancy see Session 8 on Mother's Health. Breastfeeding at night is important to ensure this effect. Oxytocin Oxytocin makes the myoepithelial cells around the alveoli contract. This makes the milk, which has collected in the alveoli, flow along and fill the ducts 21 see Figure 5.
Sometimes the milk is ejected in fine streams. Oxytocin is produced more quickly than prolactin. It makes the milk that is already in the breast flow for the current feed, and helps the baby to get the milk easily.
Oxytocin starts working when a mother expects a feed as well as when the baby is suckling. The reflex becomes conditioned to the mother's sensations and feelings, such as touching, smelling or seeing her baby, or hearing her baby cry, or thinking lovingly about him or her.
If a mother is in severe pain or emotionally upset, the oxytocin reflex may become inhibited, and her milk may suddenly stop flowing well. If she receives support, is helped to feel comfortable and lets the baby continue to breastfeed, the milk will flow again.
It is important to understand the oxytocin reflex, because it explains why the mother and baby should be kept together and why they should have skin-to-skin contact. Oxytocin makes a mother's uterus contract after delivery and helps to reduce bleeding. The contractions can cause severe uterine pain when a baby suckles during the first few days. Signs of an active oxytocin reflex Mothers may notice signs that show that the oxytocin reflex is active: If one or more of these signs are present, the reflex is working.
However, if they are not present, it does not mean that the reflex is not active. The signs may not be obvious, and the mother may not be aware of them. Psychological effects of oxytocin Oxytocin also has important psychological effects, and is known to affect mothering behaviour in animals. In humans, oxytocin induces a state of calm, and reduces stress It may enhance feelings of affection between mother and child, and promote bonding.
You and Your Hormones
Pleasant forms of touch stimulate the secretion of oxytocin, and also prolactin, and skin-to-skin contact between mother and baby after delivery helps both breastfeeding and emotional bonding 23 Feedback inhibitor of lactation Milk production is also controlled in the breast by a substance called the feedback inhibitor of lactation, or FIL a polypeptidewhich is present in breast milk Sometimes one breast stops making milk while the other breast continues, for example if a baby suckles only on one side.
This is because of the local control of milk production independently within each breast. If milk is not removed, the inhibitor collects and stops the cells from secreting any more, helping to protect the breast from the harmful effects of being too full. If breast milk is removed the inhibitor is also removed, and secretion resumes.
If the baby cannot suckle, then milk must be removed by expression. FIL enables the amount of milk produced to be determined by how much the baby takes, and therefore by how much the baby needs. This mechanism is particularly important for ongoing close regulation after lactation is established. At this stage, prolactin is needed to enable milk secretion to take place, but it does not control the amount of milk produced. Reflexes in the baby The baby's reflexes are important for appropriate breastfeeding.
The main reflexes are rooting, suckling and swallowing. When something touches a baby's lips or cheek, the baby turns to find the stimulus, and opens his or her mouth, putting his or her tongue down and forward. This is the rooting reflex and is present from about the 32nd week of pregnancy. When something touches a baby's palate, he or she starts to suck it.Endocrinology - Prolactin
This is the sucking reflex. When the baby's mouth fills with milk, he or she swallows. This is the swallowing reflex. Preterm infants can grasp the nipple from about 28 weeks gestational age, and they can suckle and remove some milk from about 31 weeks. Coordination of suckling, swallowing and breathing appears between 32 and 35 weeks of pregnancy.
Infants can only suckle for a short time at that age, but they can take supplementary feeds by cup. A majority of infants can breastfeed fully at a gestational age of 36 weeks When supporting a mother and baby to initiate and establish exclusive breastfeeding, it is important to know about these reflexes, as their level of maturation will guide whether an infant can breastfeed directly or temporarily requires another feeding method.
How a baby attaches and suckles at the breast To stimulate the nipple and remove milk from the breast, and to ensure an adequate supply and a good flow of milk, a baby needs to be well attached so that he or she can suckle effectively Difficulties often occur because a baby does not take the breast into his or her mouth properly, and so cannot suckle effectively.
Good attachment Figure 6 shows how a baby takes the breast into his or her mouth to suckle effectively. This baby is well attached to the breast.
Good attachment — inside the infant's mouth. The points to notice are: As the baby suckles, a wave passes along the tongue from front to back, pressing the teat against the hard palate, and pressing milk out of the sinuses into the baby's mouth from where he or she swallows it. The baby uses suction mainly to stretch out the breast tissue and to hold it in his or her mouth. The oxytocin reflex makes the breast milk flow along the ducts, and the action of the baby's tongue presses the milk from the ducts into the baby's mouth.
When a baby is well attached his mouth and tongue do not rub or traumatise the skin of the nipple and areola.
Suckling is comfortable and often pleasurable for the mother. She does not feel pain. Poor attachment Figure 7 shows what happens in the mouth when a baby is not well attached at the breast. Poor attachment — inside the infant's mouth. This is a classical neuroendocrine reflex; an acute stimulus tightly accompanied by a transient secretory response that persists as long as the stimulus is applied. Following the mating stimulus, the female rat secretes a nocturnal peaking between h and a diurnal peaking between h surge of prolactin 5 - 8.
The nocturnal surge is consistently greater in magnitude compared to the diurnal surge 58. These surges function to maintain progesterone secretion by rescuing the short-lived corpus luteum.
Progesterone induces changes of the endometrium allowing implantation of the blastocyst and is responsible for maintaining uterine quiescence throughout gestation. If the mating was fertile, the prolactin surges persist for 10 days 89 at which point a prolactin-like luteotrophic factor, secreted from the placenta, maintains progesterone secretion for the remainder of pregnancy.
If the mating was sterile, the female rat enters into a period of pseudopregnancy and these prolactin surges recur for 12 days 68.
Artificial stimulation of the uterine cervix is a copulomimetic model in ovariectomized rats, in which the female secretes surges of prolactin for 12 days even in the absence of a continued stimulus. Because these rats lack ovaries, this demonstrates that ovarian steroids are not required for initiation or maintenance of this unique secretory response. Conversely, in response to rising titers of oestradiol during the 4-day oestrous cycle of the female rat, prolactin secretion is sharply elevated on the evening of pro-oestrus just prior to the luteinizing hormone surge 6.
Prolactin returns to basal levels the following morning and remains there throughout the rest of the oestrous cycle. In ovariectomized animals, the administration of a bolus injection of oestradiol initiates a surge of prolactin release, which is similar in timing and magnitude to that secreted on pro-oestrus 9. The condition of having too much prolactin circulating in the blood is called hyperprolactinaemia.
The most common causes of hyperprolactinaemia include pregnancy, medications that reduce dopamine action in the body, thyroid underactivity and benign pituitary tumours known as prolactinomas. Symptoms can include the unwanted production of milk, disturbances to the menstrual cycle and symptoms due to oestrogen deficiency in women or testosterone deficiency in men.
The vast majority of patients with a prolactinoma can be treated successfully using drugs which mimic the action of dopamine. The most commonly used is cabergoline.
Prolactin - Wikipedia
What happens if I have too little prolactin? The condition of having too little prolactin circulating in the blood is called hypoprolactinaemia.
This condition is very rare and may occur in people with pituitary underactivity.