[SOUND] So there's one more factor that I want to kind of throw in here. And that is in addition to the things that I've talked about here, this is this negative inhibitory factors, the dopamine on the lactose, the releasing factor it looks like, potentially oxytocin. There's one another key thing, and that is there seems to be a kind of a feedback loop of prolactin. It's actually taken back up into the brain and then can stimulate these cells, the cells in the nuclei to make more prolactin inhibiting factor. So we have a negative feedback. Negative feedback loop. So the more prolactin is produced, the more it gets back here, the more it stimulates these cells to secrete dopamine to shut down further prolactin. So it's regulating itself in that sense. So again it's very, very complex regulatory system for prolactin. Let's take a look at some of the things that modulate this process that's going on in the hypothalamus and pituitary gland. Remember, again dopamine is the inhibitory factor being synthesized and released by these axons from these cells up in the hypothalamus. It's negative to negative effector, meaning it shuts down prolactin secretion. Other things will stimulate prolactin secretion, so let's look at some of these kinds of modulation. Estrogen, so particularly during a prepartum surge. Remember in late pregnancy, estrogen's increasing. It's getting pretty high. That actually will modify this system so that prolactin, the inhibitory factor of these is dampened down. And so you get a prepartum surge of prolactin, which is very much involved in lactogenesis. Suckling, every time the animal suckles or the cow is milked, the goat's milk whatever the case may be, you get this surge of prolactin. Again, that's impacting this so the prolactin secretion is increased. A range of different kinds of drugs and medicines can impact prolactin. So there is a dopamine antagonist that increased prolactin. Reserpine is one of those, comes from a plant. Domperidone is another one that will increase. That's a drug that's sometimes used in humans, can increase prolactin secretion. Again, it's modifying the system, it's impacting the effect of the dopamine. And then we also have other drugs that will decrease prolactin secretion, so these are dopamine agonists, so they act like dopamine and shut down prolactin secretions. So we have bromocriptine is one of those. Cabergoline is another one. And there are some other ones that are being used for that as well. So, a variety of kinds of drugs that are used to either increase prolactin or decrease prolactin. And again, they're impacting the system of the prolactin inhibiting factor or dopamine and how that's impacting or effecting the secretion of prolactin from the lactotrophs, mammotrophs. Another one down here we haven't really talked about just mentioned in passing, is daylight or day length will impact prolactin secretion. So longer days or more daylight increases prolactin, shorter days or more darkness, will decrease prolactin. So let's briefly review what we talked about in terms of prolactin. Again, it's a major hormone as we think about mammary growth, lactation, etc. So, again it's created from the lactotrophs in the anterior pituitary. There are also sources of prolactin like activity in terms of placental lactogen, coming from the placenta. A lot of species variability there. So if you're interested in that, you really kind of have to dig down to each individual species and look at how that plays out in terms of mammary growth, mammary development, and lactogenesis, and so on. And then also, a source of prolactin from the mammary gland itself. And again, this is one that we really don't have a lot of tremendous amount of information on what it's doing in the mammary gland, and how it's impacting the mammary gland. Prolactin's involved in again, in all stages of mammary development, lactogenesis, maintenance of lactation the key hormone. Certainly there are many other hormones involved in all those processes, but a key hormone in these various processes. Prolactin secretion pituitary is inhibited by a factor called dopamine or prolactin inhibiting factor, and it comes from several nuclei up in the hypothalamus and then released down the pituitary. One way or the other, there's several mechanisms by which that happens. It inhibits those lactotrophs from secreting prolactin. The modulation of this process, the modulation of the dopamine and how it impacts the lactotrophs is occurring by a number of mechanisms action of other hormones. Action of suckling, action of various kinds of drugs, day length, and a variety of other factors. So there's a lot of things that go into regulating this particular hormone, and therefore, those things will one way or the other, potentially Initially impact lactation as well as the other functions of prolactin in terms of reproduction and so on. [SOUND]