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Hormones Control of Lactogenesis and Galactopoiesis Hormone Levels at Calving Blocking Prolactin Secretion Prolactin Effects on Lactation Effect of Prolactin Secretion on Milk Yield In Vitro Lactogenesis Alpha Lactalbumin in Bovine Tissue 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Control Cortisol PRL Cortisol+PRL Control contains insulin and T3. Modifi ed from: G.T. Good man, R.M. Ake rs, K.H. Friderici and H .A. Tucke r. Endoc rinology 112:1324, 1983. ng/ml media/mg tissue/hour Progesterone on Lactogenesis Alpha Lactalbumin by Bovine Tissue 3 - PRL + PRL 2 1 0 0 10 100 1000 Progesterone (ng/ml) Control contains insulin,cortisol and T3. Modifi ed from: G.T. Good man, R.M. Ake rs, K.H. Friderici and H .A. Tucke r. Endoc rinology 112:1324, 1983. GH on Lactogenesis Alpha Lactalbumin Production 5 ng/ml media/mg tissue/h 4 3 - Prl + Prl (100 ng/ml) 2 1 0 0 10 100 1000 Growth Hormone (ng/ml) Modifi ed from: G.T. Good man, R.M. Ake rs, K.H. Friderici and H .A. Tucke r. Endoc rinology 112:1324, 1983. Hormone Priming on Lactogenesis Bovine Tissue In Nude Mice Alpha lactalbum (microgram/mg DNA) 150 100 Saline F+Prl 50 0 Saline E+P Priming (20 days) From:Sheffield, l.G. and C.W. Welsch, J. Dairy Sci, 71:75-83, 1988. Extracellular Matrix on Lactogenesis 20 Mouse Mammary Epithelial Cells Beta Casein 15 10 - Prl + Prl 5 0 -EGF + EGF Culture Prior to Lactogenesis Laminin Model of Lactogenesis Pregnancy Estrogen, Progesterone Lactation Cortisol, Prolactin Progesterone Low Progesterone Direct + indirect effects TGFa Growth P4 receptor Inhibits Lactation ECM Synthesis Epithelial cell Laminin-Rich Basement Membrane Milk Milk Protein, Other Genes Low P4 receptor Epithelial cell Laminin-Rich Basement Membrane Hormonal Regulation of Lactation Effects of Estrogen and Progesterone on Lactation Hormonal Maintenance of Lactation Hormones and the Maintenence of Lactation Insulin and Growth Hormone Throughout Lactation Growth Hormone Levels in Cattle Selected for Higher Milk Production vs. Control Cattle Prolactin Throughout Lactation Insulin, Growth Hormone and Cortisol Through Lactation Oxytocin • Oxytocin is a 9 amino acid long peptide. The amino acid structure of oxytocin is: • Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly • It has a molecular mass of 1007 daltons. Oxytocin has a disulfide bond between the two cysteines. Reduction of the disulfide bond inactivates oxytocin. One IU (international Unit) is approximately 2 micrograms of pure peptide. Oxytocin Synthesis • Oxytocin is synthized in the hypothalamus in specific nuclei, the paraventricular nucleus and the supraoptic nucleus in the hypothalamus. [A cluster of nerve cells in the brain is often called a nucleus. This is different from the nucleus of a single cell.] Neurons in these hypothalamic nuclei synthesize the oxytocin precursor and package it into vesicles. Oxytocin is initially synthesized as a large molecular weight precursor which also consists of the oxytocin-carrier peptide neurophysin. The precursor is proteolytically cleaved in the neuron in the oxytocincontaining vesicle to yield oxytocin bound to neurophysin. The oxytocinneurophysin complex is the intracellular storage form of oxytocin. • The oxytocin-containing vesicles are transported from the cell body (which is in the hypothalamus), down the axons to the neuron endings in the posterior pituitary. This is called the hypothalamo-neurohypophysial tract. The oxytocin-neurophysin complex is stored in neurosecretory granules called herring bodies in the axon ending. Pituitary Gland Serum Oxytocin (µU/ml) 35 Oxytocin Release at Milking 30 25 20 15 10 5 0 -25 -20 -15 -10 -5 Premilking Stimulus 0 5 10 15 20 25 30 MINUTES Machine on Prolactin Concentration at Milking Alveolus Stained to Show Myoepithelium Myoepithelial Cell Milk Letdown Reflex Milk Letdown Alveolar Contraction Oxytocin Release and Half-Life • It is estimated that the bovine pituitary has about 800 micrograms of oxytocin. This is about 40X what is in the blood under resting conditions. Only about 1/3 of pituitary oxytocin is released at a milking. • Oxytocin receptors on myoepithelial cells can respond to very low levels of oxytocin. • Oxytocin has a short half-life in the blood = 0.55 to 3.6 min. This means that the removal of milk by machine or by nursing must be closely timed with stimulation of the teats. Factors Modifying Milk Letdown • Autonomic nervous system – Stress gives epinephrine release – Inhibits oxytocin release – Inhibits myoepithelial cell contraction – Inhibits blood flow to udder • Conditioned reflex – Letdown in response to sights, sounds associated with milking Interesting Stimulation of Milk Letdown Adrenal Medulla Posterior Pituitary Udder Vasculature Ihnibits oxytocin release Inhibits Blood Flow Epinephrine Myoepithelium Inhibits Contraction Medulla Adrenal Milking Apparatus Teat Cup Structure Milking Stimulus and Oxytocin Release Udder S timulation on Milk Flow Rate 5 Milk Flow (kg/min) Stimulus 4 3 2 No Stimulus 1 0 0 1 2 3 4 5 6 Minutes Since Machine On 7 8 Residual Milk • Left in udder after normal milking • About 10% of milk • Can remove with oxytocin Phase Separation and Residual Milk Removing Residual Milk • Oxytocin injections – Expensive – Not approved use • Machine stripping – High incidence of liner slips – Increases mastitis risk • Udder massage – Second oxytocin release. Udder Pressure and Milk Secretion Milk Letdown and Mammary Pressure Effect of Exogenous Oxytocin on Milk Yield