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Pharmacodynamic Terms: Receptor, Agonist and Antagonist (Nursing)

by Rhonda Lawes

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    00:01 Okay, now we’re going to talk about receptors and their partners: the agonist and the antagonist.

    00:07 So, those are 3 words—pause for just a moment and just kind of get straight in your mind. Receptors are very uniquely shaped and they either receive agonists or antagonists.

    00:18 Ready? Let’s go through a little more definition. Okay, so receptors are these really unique protein molecules. They receive only specific chemical signals, so they have special shapes and attractions, and when they receive these signals, it either blocks the activation of that receptor or it activates the reception. Okay, so I know that I have receptors, they’re really unique, only certain substances will connect with them, and either it’s an agonist which causes that receptor to be activated, or it’s an antagonist that will block the activation of that.

    00:54 So what types of things can be agonists or antagonists? Well, they can be drugs, hormones, or neurotransmitters.

    01:02 Obviously, we’re going to focus more on drugs at this point, but we’ll also talk a little bit about hormones and transmitters. Okay, so you understand what a receptor is—it’s this special receiver.

    01:14 Now, let’s go over agonists and antagonist again. When an agonist connects, it’s like a lock-and-key mechanism, when an agonist connects or binds to a receptor, it activates that receptor to do what it’s intended to do.

    01:28 So, if I was trying to get into my house, if I had the right key to my house, i it would fit in the lock, it would be an agonist, and it would unlock the door.

    01:38 Now, if I had an antagonist, if I tried to put the wrong key in the door, it might fit, but it wouldn’t activate that receptor or unlock the door. So let’s use another example, sometimes have you ever gotten an advertisement from a car dealership that they give you a key, and says, “Hey! Bring this key to the car dealership, and if it starts the car, you win the car!” Okay, yeah. I’ve never won a car but that’s another thing. So, let’s take a look at this. Now, if you take a look at the drawing that I have up here, first of all, you see the receptor, and see that it has a very unique opening.

    02:18 Then you see all those other keys floating around.

    02:20 Those are agonists and antagonists, but only certain ones are going to fit in. Now, you see the agonist slide in. See! It fits.

    02:31 That’s a beautiful thing and it will see the lightning bolts that let you know that it activates that receptor.

    02:37 So that’s a really good thing.

    02:39 You have a uniquely shaped receptor, you have an agonist that connected, bound to the receptor, and then whatever that receptor is intended to do, it will activate it.

    02:49 Now, let me give you an example of some receptors in your own body.

    02:53 You have beta-1 receptors on your heart, you have beta-2 receptors on your lung. When an agonist hits the beta-1 receptors on your heart, it pumps faster and harder. When an agonist hits the beta-2 receptors on your lungs, your lungs will bronchodilate. Now, you need both of those responses when adrenaline, or epinephrine, is released in your body because the sympathetic nervous system is in gear.

    03:18 So, that’s an agonist. Now, let’s show you again what happens with an antagonist.

    03:22 You’ll see that we have the same receptor (look, it’s got a similar shape), but instead of an agonist binding to the receptor, you end up with an antagonist making it.

    03:33 It still fits, still has a connection, but you see like the good guy, it can’t get in there because the antagonist has blocked the activation of that response. Now, let’s go back to those beta receptors. Remember I said that you had beta-1 receptors on your heart? If a beta- adrenergic agonist, or we call them beta-blocker, that’s a drug, if we give the patient a drug, a beta-blocker that acts just like it’s an antagonist.

    04:01 So, the drug binds to the receptor, so when epinephrine is released into your body, your heart rate will not go up because there’s an antagonist blocking the activation of that receptor.

    04:14 Now, we use receptors, agonists, and antagonists in all kinds of treatment plans.

    04:21 So, it’s really important that you understand that.

    04:23 So let’s keep talking about some other types of drugs. Now, we have natural agonist and those are called endorphins.

    04:29 They’re natural agonists that bind to the opioid receptors.

    04:33 Now, the opioid receptors are the feel- good receptors of the body, right? People swear to me that run that if you can get a runner’s high, if you can run long enough, but frankly, I have never experienced a runner’s high.

    04:46 Maybe I just haven’t ran long enough to make that happen, but when the natural agonists, my natural endorphins connect to my opioid receptors, they produce pain relief and euphoria, so you just feel good.

    04:59 Now, one of our patient’s, if they are experiencing pain, we want to give them an agonist drug.

    05:04 Hey! That’s really cool.

    05:05 So, the agonist drug, morphine, acts just like the natural substance in my body endorphins because in an agonist drug like morphine also binds to opioid receptors.

    05:17 So, how am I going to feel? Pain relief and euphoria. That’s really cool because agonist drugs are similar enough, the drugs that we’ve created are similar enough, to the natural endorphins in my body that they will bind to the same receptors.

    05:32 That, is a really cool thought. So, let that sink in a little bit because that’s all of what we do in pharmacology.

    05:39 We take things that normally occur in your body and we create a substance that, when manipulated, in a way to get the effect that we want. So, you end up with the same, or even a little better reaction of that pain relief and euphoria when we give you morphine. So, let’s talk about the reverse agonists. Now, earlier we talked about beta-blockers, so I want you to compare that same example with the same drug morphine.

    06:06 So, we already talked about morphine— it’s an agonist drug that binds to opioid receptors, right? Agonist drugs are similar enough that they fit and they connect, and they produce that same or even stronger euphoria, but we have drugs that can act as antagonists.

    06:22 So, remember we talked about affinity, in the beginning of the video? Now, when I have a drug like morphine that’s bound to those opioid receptors, what if the patient’s received too much? They’ve got too much morphine. Well, it’s a respiratory depressant, this could put the patient in a lot of trouble.

    06:40 So, we want to boom! We want to knock that morphine off those receptors.

    06:45 What do we do? Well, we can use a special kind of antagonist.

    06:49 We call it naloxone or Narcan.

    06:51 You may have actually seen this in the news where they’ve put it in a nose spray now where police officers are using this if they come against someone who has an opioid overdose or if you are someone who is around people who have an addiction problems, this is a good thing for you to have with you.

    07:06 But naloxone, or Narcan, is an antagonist to opioid receptors, so that means it will bind to the receptor and then morphine can no longer bind to that receptor.

    07:18 It will exactly reverse morphine or even a heroin overdose in seconds. Now, I have seen this happen. It is dramatic.

    07:27 When you have someone that comes in, and they’re in an opioid overdose, and we give them Narcan—usually in the ER, it would be, obviously, in an IV dose, but you give them this and boom! They wake back up, so it is a really fast, fast reaction.

    07:42 Not all antagonists are that dramatic, but that’s a good example for you to understand the concept of antagonists when we do that.


    About the Lecture

    The lecture Pharmacodynamic Terms: Receptor, Agonist and Antagonist (Nursing) by Rhonda Lawes is from the course Pharmacology and Implications for Nursing.


    Included Quiz Questions

    1. Drugs
    2. Hormones
    3. Neurotransmitters
    4. Receptors
    5. Target cells
    1. Causes the associated cellular process to be blocked
    2. Causes the associated cellular process to be activated
    3. Increases the heart rate
    4. Stimulates bronchodilation in the lungs
    1. Naloxone
    2. Morphine
    3. Endorphin
    4. Flumazenil
    1. Endorphins
    2. Epinephrine
    3. Norepinephrine
    4. Fentanyl
    1. Receptors
    2. Agonists
    3. Antagonists
    4. Endorphins

    Author of lecture Pharmacodynamic Terms: Receptor, Agonist and Antagonist (Nursing)

     Rhonda Lawes

    Rhonda Lawes


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