Physiology of the breasts
High concentrations of oestrogen, growth hormone, and glucocorticoids stimulate the breast ducts to proliferate during pregnancy. Progesterone and prolactin stimulate alveolar growth (63).
From 34 months until the first 30 hours after delivery the breasts secrete a thick, protein-rich fluid called colostrum. This is stimulated by prolactin and placental lactogen. During pregnancy, the high levels of oestrogen and progesterone prevent alveolar transcription of alpha-lactalbumin, the protein contained in milk, thus preventing full lactation. Following delivery, the sudden decrease in progesterone and oestrogen levels allows prolactin to act directly on the alveolar cells to stimulate synthesis of milk (64). Suckling sends impulses to the hypothalamus which stimulates release of prolactin and oxytocin. By day 5 after delivery, milk production is at full flow of approximately 500-1000 ml/24 hours (65). This demands an additional 500 kcal intake per day of the mother. Oxytocin causes the myoepithelial cells to contract and milk to be ejected. This reflex may be inhibited by catecholamine release or adverse environmental or emotional factors (66).Clinical considerations
• Dopamine antagonists such as bromocriptine act as prolactin antagonists and prevent milk production.
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