Ep #160: Alpha & Beta Adrenergic Receptors Explained: NP Pharmacology Review

Welcome to the Real Deal Nurse Practitioner Club, the podcast for nurses who are ready to pass their boards and thrive in their careers as real deal nurse practitioners. I’m Anna and I’m the Director of Nursing Content at Blueprint Test Prep. Whether you’re deep in exam prep or stepping into practice, I’ve got you. It is time to become the confident, knowledgeable NP that you’re meant to be. Let’s dive in. 

Anna: Hey everyone. Welcome back to the Real Deal Nurse Practitioner Club. I’m Anna, and today, we are starting our next three weeks of episodes focused on what we call 3P content. And that’s going to be patho, pharm, and physical assessment.

Now, we’ll do a whole episode on tips to pass your 3P exam in a few weeks. But this episode and our next large episode are going to focus on some topics that might be included on that. 

This episode is focusing on the pharmacology P, and it’s a topic that tends to seem kind of nitty-gritty, but it is really important to learn, and that’s going to be alpha and beta adrenergic receptors. And here’s the thing with these. Once these click, a huge amount of pharmacology will make sense, and then you can use that baseline knowledge to critically think through questions on your certification exam to become a real deal NP.

Alex: Yes, this is one of those topics where people try to memorize really long lists, but if you really understand these receptors and how medications interact with them, you don’t actually need to memorize nearly as much.

Anna: Yeah, exactly. So we are going to break this down in a way that is intuitive and practical. So we’re going to review some of the nervous system basics that you’re going to want to know, and I promise there is no need to fret here. We’re not reading a textbook. We’re just going to focus on a couple key points. 

And then we’re going to talk through what alpha and beta receptors actually do. And then we will connect that to real medications that you’re going to prescribe as a real deal NP. And then we’ll finish with a quick clinical scenario that we can talk through so that you’ll really see how this info can help your studying and your real life as an NP.

All right. Alex, do you want to get us started?

Alex: For sure. So, let’s kick off with a quick recap on the nervous system. At the highest level, the nervous system splits into two parts, the central and the peripheral nervous system. So the central nervous system includes the brain and the spinal cord, and the peripheral nervous system basically includes everything else. 

And within that peripheral nervous system, we care most about two branches. And so the first one is the somatic nervous system, which controls voluntary movement. The autonomic nervous system controls automatic functions like heart rate, digestion, blood pressure. So think auto for autonomic and automatic to help you remember those.

Anna: Yeah, and then that autonomic nervous system splits again into that sympathetic and parasympathetic. And remember, sympathetic is that flight or fight, and then parasympathetic is the rest and digest system. So I always think of like eating a pear here for parasympathetic to remind me that it is the rest and digest one. 

But for today’s episode, we’re living almost entirely in the sympathetic nervous system or that fight or flight area, because that’s where most alpha and beta adrenergic receptors live.

Alex: Yes, the sympathetic nervous system runs on a group of neurotransmitters called catecholamines. Do you remember which ones I’m talking about? The biggies are epinephrine and norepinephrine, and these are released during times of, you know, the body senses stress. Or it could be real danger, or it could be exercise or illness, or even anxiety about your upcoming certification exam. And they are essentially trying to prepare your body to respond to that specific stressor.

Anna: Yeah, and a big thing here is that our body, it can’t always tell the difference between something like illness or anxiety stress with real danger or emergency stress. So really think about what the body needs in a survival situation. Right? We need a faster heart rate with increased contractility, higher blood pressure, more glucose. And because your energy is being spent in those vital places, there is less energy spent on things like digestion.

Now, catecholamines deliver all of that by binding to alpha and beta receptors throughout the body. So now that we’ve refreshed on all of those basics, here is where the pharmacology comes in. Many medications either mimic these effects or they block them. And so let’s just start with the alpha receptors. We have alpha one and alpha two receptors that we’re going to talk about. But Alex, can you start us off with alpha one?

Alex: Absolutely. Alpha one receptors are mostly found in vascular smooth muscle, the GU system, the GI tract, and more. Now, when alpha one receptors are activated, the big effect here is constriction. Now, that isn’t everything, but that is the main thing we are going to focus on for simplicity here. So think, alpha one constricts. 

So with that in mind, clinically, alpha one activation causes things like constriction of those blood vessels, so increased blood pressure, tightening of the sphincters in the GU system, so urinary constriction, decreased GI motility. So as for alpha one agonist medications, these are great for things like nasal congestion. They shrink or constrict those swollen blood vessels. An example here is Afrin. Midodrine is an alpha one agonist that treats low blood pressure because it helps those vessels constrict to bring up the blood pressure when it’s low.

Anna: Yeah, and then on the flip side, alpha two receptors are found on presynaptic nerve terminals, which just means they sit on the sending side of sympathetic neurons. And their main job is to act like a brake or an off switch. So when the alpha two receptors are activated, they reduce the release of norepinephrine. 

So instead of turning the sympathetic nervous system up, they actually turn it down, which can lead to lower blood pressure and decreased sympathetic outflow. And that’s why alpha two agonists like clonidine and methyldopa are used to treat hypertension. Right? They quiet the system rather than stimulating it.

All right. Now let’s move on into beta receptors, and we’re going to start with the most tested one here, and that’s beta one.

Alex: I always immediately think of the heart with beta one, which is where they primarily sit, but they are also in the kidneys. So when activated, they increase the heart rate, increase contractility, increase blood pressure. So anytime you hear beta one, think cardiac stimulation. That’s why beta one agonists like dobutamine are used in severe heart failure or cardiogenic shock. You ICU nurses might, this might sound a little familiar here, because they increase cardiac output by boosting that heart function.

Anna: Yeah, and then with the beta two receptors, these are more widespread. So you’ll find them, well, I always like immediately think of the lungs here. Right? I always think beta one, you have one heart. Beta two, you have two lungs. But you’re also going to find them in places like the blood vessels, the GI and GU smooth muscle, the liver, the pancreas. Ultimately, the activation of beta two receptors leads to smooth muscle relaxation.

Alex: Yes, and clinically, that leads to things like bronchodilation or vasodilation. So that’s why beta two agonists like albuterol are so, so effective for asthma or COPD. They relax airway smooth muscle to make it easier to breathe.

Anna: Now, one little side note, I just have to say it, but I don’t want to focus on it. I’m going to mention there are technically beta three receptors. These are way less likely to be tested on, but they’re just relevant enough to mention. These are found mainly in like adipose tissue and the bladder, especially the detrusor muscle. 

Now, when beta three receptors are activated, it causes that detrusor muscle to relax, which is why they can be used for treating conditions like an overactive bladder.

Now, really a key point here for this podcast is there are both agonists and antagonists when it comes to any of these receptors. And this is really where you need to know the difference. But having that basic background of what each receptor does will allow you to figure out how it works when combined with this key agonist-antagonist pharmacology concept. 

So remember, agonists activate the receptors, and antagonists are going to block the receptors. So for example, an alpha one agonist increases vasoconstriction. It is activating that receptor. But an alpha one antagonist does the opposite.

Alex: Yes, and that’s why alpha one blockers or alpha one adrenergic antagonists like tamsulosin are used for BPH, the prostate. They relax smooth muscle tissue in the prostate and bladder neck, which improves urine flow. And think about those beta blockers. They block beta one receptors leading to lower heart rate, lower blood pressure, and reduced myocardial oxygen demand. 

So another key point to know here, there are cardioselective beta blockers like metoprolol and atenolol, which focus mostly on beta one receptors in the heart. But just know that there are also non-selective beta blockers like propranolol, which can affect the receptors in both the heart and the lungs. So that is why we don’t give non-selective beta blockers to certain patient groups like those with asthma.

Anna: Yep. All right, let’s bring this together with a quick case scenario. Let’s say we have a 47-year-old patient. They have type two diabetes, and they are being started on propranolol for migraine prevention. Alex, what is one major education point you would want to give this patient?

Alex: Great question. Do you all know the answer here? So while we always want to teach patients all about their medications, there is a very key safety point here, and boards love safety points. Propranolol is a non-selective beta blocker, meaning it blocks both beta one and beta two receptors. So by blocking those beta receptors, it can actually mask the typical symptoms of hypoglycemia like tremors, palpitations, sweating, anxiety.

Anna: Yeah, so the patient may not feel their blood sugar dropping until it’s dangerously low. So our education should include more consistent blood glucose monitoring and awareness that symptoms may feel a lot more subtle so that they’re not relying on how they feel solely to detect lows.

Alex: And this is a key example of how understanding those receptors helps you work through the question rather than just memorizing long lists of side effects.

Anna: Yeah, you’re never going to be able to remember every single nitty-gritty detail that’s going to be tested on, but when you have these basics down, you can really critically think your way through those questions that you don’t know. 

And it’s really not so scary once it’s broken down, right? So just take the time to understand alpha and beta receptors and how medications interact with them. Because once you know where the receptor lives and what happens, right, when it’s activated or blocked, pharmacology becomes a lot less overwhelming.

Now, if you want deeper dives like this with practice questions, with visuals, with real-world application, check out our full review courses. We walk through pharm in a way that actually sticks. But thank you for hanging out with us today in the Real Deal Nurse Practitioner Club podcast. And we will see you next time. Happy studying.