Lactation: The final phase of mammalian reproduction BIOL30001 Reproductive Physiology Lactation, G Shaw BIOL30001 Reproductive Physiology Lactation: The final phase of mammalian reproduction Geoff Shaw

References EssRep7 Chapter 18 J&E6: Chapter 14. Hormonal control of lactation, A.Cowie in Hormonal Control of Reproduction: Austin & Short. Book 3, Chapter 8: Physiology of Reproduction 1994 4th Ed. Knobil & Neill: Chapter 56, p.1099:Control of Mammary Gland Growth and Differentiation. W. Imagawa, J. Yang, R. Guzman & S. Nandi Chapter 57, p.1065 :Lactation and Its Hormonal Control. H. Allen Tucker Chapter 59, p.1131:Milk Ejection and Its Control. JB. Wakerley, G. Clarke & A.J.S. Summerlee Lactational control of Reproduction, A.S. McNeilly, in Reproduction Fertility and Development (2001) 13: 583-590 Margaret C. Neville. (1998) Milk Secretion: an overview. http://mammary.nih.gov/reviews/lactation/Neville001/index.html

Lactation Primary source of nutrition and energy for newborn mammal Immune protection Mammary glands change – hormones and development Variation between species: eg number of glands: human 2; wallaby 4; pig 18; cow 4 (apposed in single udder)

Milk composition varies with species Component (g / 100 mL) Human Elephant Seal Water 90 35 Protein 1.1 10 Carbohydrate 7.5 2 Lipid 4.2 55 Energy (MJ / L) 3.3 23

Structure of a mammary lobule eg. cluster of alveoli in the goat myoepithelial cells arteriole alveolar epithelial cells venule capillaries milk Alveolus milk duct From Austin and Short 1984

Structure of mammary lobules and alveoli Note vascular supply around alveolus myoepithelial cells surrounding alveolus contract, increasing intra-mammary pressure at milk let-down J and E, Fig 14.3

duct systems in different species 15-20 mammary lobes Dilating as a lactiferous sinus emerging at nipple J and E Fig14.2

Development of mammary gland in fetal mouse Ovariectomised female Normal female Normal male Castrated male androgens cause regression of the mammary primordia From Austin and Short 1984

Postnatal mammary growth in rat pre-pubertal late-pregnancy  lactation pubertal Oestrogen, progesterone, cortisol, growth hormone, placental lactogen and prolactin needed for mammary growth during first pregnancy post- pubertal From Austin and Short 1984 cyclic changes through oestrous / menstrual cycles

Mammary gland cycle http://mammary.nih.gov/atlas/wholemounts/normal/index.html

Summary: structure and development Mammary gland: Structure of mammary gland – variations on a theme ducts and cisterns alveoli open into milk ducts ducts join and empty via nipple or teats. galactophores are common ducts leading to teat: rabbits 6-8; man 15-20; agile wallaby approx. 20. supernumerary teats Fetal development present in both sexes but poorly developed in men Regress in male mice and rats as a result of androgens Development after birth full growth not achieved until end of puberty or in early lactation

Hormonal regulation of milk secretion differs between species To maintain high milk production after removal of the pituitary gland: Rats need: Prolactin Adrenocorticotrophin Sheep & goats need: Growth hormone Prolactin Adrenocorticotrophin* Thyrotrophin† Rabbits need: Prolactin Milk secretion requires hormonal support but species’ needs vary ACTH maintains cortisol secretion from the adrenal gland † TSH maintains thyroid hormone secretion from the thyroid gland

Milk secretion: hormonal control Mammary gland transplanted to the neck of a goat (Jim Linzell’s experiment) separated from nerve supply continued milk secretion Control is hormonal, not neural However milk removal necessary for continued lactation (Malcolm Peaker)

Pregnancy, hormones and milk secretion Onset of lactation in women Colostrum high protein rich in immunoglobulins Mature milk 7% lactose 4% fat 1% protein +minerals, vitamins etc Two 25 mL samples of human breast milk. The left hand sample is foremilk, the watery milk coming from a full breast. The right hand sample is hindmilk, the creamy milk coming from a nearly empty breast http://en.wikipedia.org/wiki/Human_milk J & E 14.5

pregnancy  mammary gland development high progesterone and oestrogens hPL (hCS) prolactin peripartum  transition to lactogenesis fall in progesterone and oestrogens no hPL slow fall in PRL  needs nipple stimulation (suckling) to maintain PRL and milk production

Local regulation FIL – Feedback inhibitor of lactation Small protein secreted in alveolus If not removed by emptying alveolus, it acts to suppress further milk secretion.

Mammary secretory processes Milk Fat Globule exocytosis: proteins made via RER and Golgi; Lactose apocrine secretion of lipids; vesicle membranes  phospholipids trans-membrane: water; small molecules; drugs trans-cytosis: immunoglobulins; some hormones & growth factors paracellular: immune cells; leakiness may be high in disease states increasing transfer of interstitial fluids. http://mammary.nih.gov/reviews/lactation/Neville001/index.html

lactation Milk secretion Initiation of milk secretion begins in pregnancy Prolactin and other hormones Synthesis of milk constituents within alveolar cells Intracellular transport of milk components Discharge of constituents into alveolar lumen Local control - FIL Milk removal Passive removal of milk from cisterns and large ducts Stimuli Sucking Sights, smells, sounds, tactile stimuli associated with suckling Reflex ejection of milk from alveoli (‘let down’ or ‘draught’) Oxytocin

Milk secretion: The importance of sucking Sucking induced release of prolactin. Prolactin VIP = Vasoactive intestinal peptide , VIP a potent Prl releasing factor Dopamine from TIDA nerves, - DA a Prl release inhibitory factor EssRep7 18.6

The milk ejection reflex Sucking-induced release of oxytocin. EssRep7: 18.7

Milk ejection: Anticipation of milking on oxytocin concentrations in dairy cows PM preparation for milking; MA application of teat cups; S stripping; C control level. From Austin and Short 1984

Milk ejection: the role of oxytocin Hottentot method of inducing milk let down (Ferguson Reflex)

Milk ejection: Oxytocin receptors regulate response Oxytocin receptors during pregnancy and lactation in rat mammary gland from Soloff and Weider 1983

Hormonal control of lactation: consists of milk secretion and milk removal stages. Maintenance of lactation usually requires several anterior pituitary hormones prolactin is critical in non-ruminants, and growth hormone in ruminants. Oxytocin essential for milk ejection. Milk removal essential for continued lactation responses mediated by receptors.

Milk composition: Changes in peripartum period colostrum Milk composition in women pre- and post-partum. 0 indicates time of birth From Kulski and Hartmann, 1981

Milk Composition: Colostrum: post-partum secretion high in protein, sodium and chloride. also antibodies (IgG and IgA). Milk: large species differences in concentrations of milk fat, lactose, protein and water. Milk fat mixture of lipids: triglycerides, diglycerides, monoglycerides, free fatty acids, phospholipids and sterols. Arctic, aquatic, desert mammals produce milk with 75% energy in lipid fraction Frequent nursing species produce milk with lower nutrient density

Lactation in marsupials Lipids Proteins Carbohydrates Milk composition changes in marsupials From Green 1984

Milk ejection in the agile wallaby - concurrent asynchronous lactation difference in response to OT allows milk ejection in gland with PY continuously attached sucking by young at foot causes ME in both glands intra-mammary pressure from Lincoln and Renfree 1981

Prolactin related suppression of reproductive cycle sucking stimulus Dopamine and agonists (bromocriptine) inhibit prolactin synthesis. High levels of Prolactin in lactation inhibits GnRH. pituitary LH response to GnRH reduced, failure of positive feedback ovarian response to LH same. naloxone (opiate inhibitor) also inhibits prolactin release (alternate pathway) nipple spinal cord hypothalamus β-endorphin release - - dopamine release GnRH pulse generator oxytocin - prolactin milk production lactational infertility milk ejection

Contraceptive effects of breastfeeding Non lactating, no contraception Lactating, no contraception Probability of pregnancy Cumulative % % women amenorrheic -▽- Monthly % risk of pregnancy Months postpartum Months of lactational amenorrhoea Post partum, lactating + post menstrual contraception Short RV, Lewis PR, Renfree MB, Shaw G (1991) The contraceptive effects of extended periods of lactational amenorrhoea. The Lancet 337, 715-717.

Lactational control of hormonal cycles: Lactational control of reproduction: Prolactin release important in suppressing cyclic release of gonadotrophins. Endogenous opiates (beta endorphins) are also involved. Frequency of suckling very important in lactational amenorrhoea

Summary nutrition, energy, water, immune protection for newborn mammary gland has multiple lobules alveoli  secretory epithelium myoepithelial cells  OT & milk ejection well vascularized development induced by hormones – prolactin, Prog, E2 etc placental lactogens in pregnancy initially colostrum (immunoglobulins)  mature milk oxytocin & Fergusson reflex + CNS lactational control of reproductive cycles - role of endorphins anoestrus diapause