I.	Galactopoiesis

	1.	Requires hormones and removal of milk
		A.	Without frequent emptying of the mammary gland, 
			milk synthesis will not persist.
		B.	Conversely, maintenance of intense suckling 
			or milking stimulus will not maintain lactation 
			indefinitely.

II.	Hormonal Control of Galactopoiesis

	1.	Prolactin

		A.	Historically thought to be the primary component 
			of the galactopoietic complex
			a.	Galactopoietic in monogastric animals
			b.	Not necessary for galactopoiesis 
				in ruminants
				i.	Inhibitors of prolactin don't 
					suppress lactation
				ii.	Milk yield slightly reduced in ewe
				iii.	Prolactin will increase milk yield 
					if given endogenously
				iv.	May play minor role
		B.	Suckling or milking induces Prolactin surge in blood
			a.	Decreases Dopamine
			b.	May stimulate next round of secretory 
				activity
			c.	Response declines with advancing lactation
		C.	Temperature and Light also stimulate prolactin
			a.	Warmer temperatures and artificial lighting 
				in winter and fall can increase mammary 
				development and milk yield  

	2.	Somatotropin

		A.	Nursing increases release of ST in rats and goats, 
			but not cows and humans
		B.	Blood ST decreases with advancing lactation
			a.	May be due to lack of TRH
		C.	Galactopoiesis
			a.	Little effect of ST in rats
			b.	Very galactopoietic in ruminants
				i.	Necessary to maintain lactation
		D.	bST treatment in cattle
			a.	Mass produced using biotechnology
				i.	Made in bacteria
			b.	Increases milk yields
				i.	10% early to mid-lactation
				ii.	Up to 40% in late lactation
			c.	Only FDA approved for pregnant animals
				i.	May alter fertility
			d.	Treated cows adjust nutrient intake 
				to support increase milk production
				i.	Long term treatment
			e.	Does not affect cow's health other than 
				problems normally associated with high 
				milk production
			f.	Increases synthesis of lactose, fat, 
				and protein
				i.	Coordinates changes in tissues 
					and physiology
				ii.	Milk composition altered 
					very little

	3.	Placental Lactogen

		A.	Galactopoietic in cattle
			a.	Endogenous PL increases milk yield
			b.	Different mechanism than ST
		B.	Probably plays a role in maintaining lactation 
			during pregnancy

	4.	Glucocorticoids

		A.	Essential for maintenance of lactation
			a.	Adrenalectomy severely impairs lactation
		B.	Seems to affect expression of casein genes the most

	5.	Thyroid Hormones

		A.	Essential for maximal secretion of milk
		B.	Injections will increase milk production
			a.	Increases feed intake
			b.	Short term

	6.	Ovarian Steroids

		A.	Ovariectomy has no effect on postpartum mammary 			
			growth or lactation
		B.	Pharmacological levels of Estrogens will decrease 
			milk yield
		C.	Progesterone has no effect
			a.	No receptors in mammary gland during 
				lactation
			b.	May have some anti-glucocorticoid effects, 
				but affinity for receptor is low

	7.	Autocrine Factors

		A.	Local factors are also important
			a.	Milk secretion is only increased in mammary 
				glands that have milk removed
				i.	Can't be system hormones since 
					whole mammary gland is exposed
				ii.	Also not intramammary pressure 
					related
			c.	Evidence for autocrine or paracrine factors 
				yet unknown

		B.	Feedback Inhibitor of Lactation (FIL)
			a.	A whey protein (10-30 kDa)
			b.	Negative feedback on milk synthesis 
				by alveolar cells
				i.	Reduces secretory rate
				ii.	Reduce key enzymes for synthesis
				iii.	Stimulates degradation 
					of intracellular caseins
				iv.	Reduce PRL receptor numbers
				v.	Inhibits mammary cell differentiation				

III.	Role of Milk Removal in Galactopoiesis

	1.	Milk Removal is required for maintenance of lactation

		A.	No evidence for nerves directly controlling 
			secretory activity
			a.	Transplant studies
		B.	Milking stimuli without milk removal 
			a.	Retards losses in mammary cells 
				or metabolic activity
		C.	Acute accumulation of milk
			a.	Increases intramammary pressure
			b.	Activates sympathetic nervous system
			c.	Decrease mammary blood flow
			d.	Decreases hormones to mammary gland
			e.	Will eventually cause cell apoptosis
		D.	Nursing stimulus
			a.	Triggers release of galactopoietic hormones
				i.	Especially PRL
			b.	May stimulate next round of secretory 
				activity
		E.	Replacement of young with foster litters can 
			prolong lactation for up to one year in rats
		F.	In cows, if you do not milk two quarters 
			for two weeks, but continue milking other two
			a.	Milk will return to two quarters 
				at lower yield than controls
			b.	Next lactation the experimental quarters 
				will produce more milk
	2.	Stimulation intensity
		A.	Increased suckling or milk removal increases total 
			milk produced
			a.	3X or even 4X a day milking becoming more 
				and more common
				in dairy operations