Autonomic Drugs/Receptors Flashcards
Mechanism of Alpha 1 receptors:
Gq coupled receptor. Gq pathways activate IP3 and DAG from membrane phospholipids. IP3 released intracellular calcium stores, which causes SMOOTH MUSCLE CONTRACTION
Mechanism of Alpha 2 receptors:
Gi coupled receptor. Gi pathways inhibit adenylyl cyclase, which is responsible for the formation of cAMP under normal circumstances.
When blocked, there is a DECREASE in cellular cAMP.
What type of G protein is coupled with B1, B2, and B3 receptors? What is its mechanism?
Beta receptors are Gs coupled receptors. They stimulate Adenyate Cyclase to cause INCREASE in cellular cAMP levels.
This increase in cAMP levels causes different outcomes in different target cells, however. If B2 receptors in the heart are stimulates, it causes increased HR/contractility. If B2 receptors in skeletal muscle are stimulated, there is smooth muscle relaxation and vasodilation.
Dopamine 1 receptors are paired with which type of G protein?
Gs (increase cellular cAMP via adenylate cyclase stimulation)
You’re having a bronchospasm. What class of drug would you give to make it stop?
B-agonist
Drug of choice for anaphylactic shock
Epinephrine
Norepinephrine has an effect on which sympathetic receptors? Which one is left out?
Norepinephrine effects a 1&2, and B1.
No action on B2
MOSTLY EFFECTS ALPHA RECEPTORS (vasoconstriction, increase BP), with a slight B1 effect (increase in HR/contractility)
Alpha receptor antagonist drug names end in what?
a1 “specifics” end in “azosin.”
Teferazosin
Prazocin
Doxazocin
A1=A2 end in “amine”.
Phenoxybenzamine
Phentolamine
Which alpha antagonists are dose specific? explain.
Phenoxybenzamine and PHENTOLAMINE
LOW DOSE: specificity for a2 receptors on the presynaptic membranes of sympathetic neurons. Blocking alpha 2 receptors blocks their normal negative feedback of Norepinephrine, so there are inotropic (cardiac stimulatory) effects.
- increases BP because NE is not inhibited.
HIGH DOSE: greater Alpha 1 specificity. Blocking alpha 1 receptors causes vasodilation and a decrease in BP
Drugs with more alpha 2 blocking ability will have what effects on the heart?
Drugs with more a2 blocking ability will lead to INOTROPIC effects:
Tachycardia
Greater CO
Increased BP
This is due to the increased release of Norepinephrine. There is no negative feedback of NE due to loss of a2 receptors.
Drugs with more alpha 1 blocking ability will have what effects on the heart? Vasculature?
Blocking Alpha 1 receptors relates to smooth muscle contraction. This won’t have too much effect on the heart except for smooth muscle relaxation of the peripheral vasculature, which LOWERS THE BP. There may be a compensatory increase in HR.
The drugs block the already-circulating E and NE from binding alpha receptors and inducing vasoconstriction.
Adverse Effects of Alpha Blocker Therapy:
Initial dose can cause Orthostatic Hypotension. So take it before bed and with food.
Can cause sinus tachycardia, angina (chest pain with exertion), and heart palpitations.
Which Alpha Blocker should only be used in emergency HTN situations?
Phentolamines
(Remember: blocks a1 at high doses for a decrease in TPR and BP, and at low doses, blocks a2 for a cardiac stimulatory effect)
Why aren’t alpha blockers used frequently anymore?
They have an increased risk of heart attack, compared to the use of diuretics for HTN therapy.
Which alpha blocker covalently binds to block its target receptor?
Phenoxybenzamine – LONG duration of action because the
Orthostatic Hypotension is the biggest problem in which Alpha Blocker?
Prazocin
What is the general rule of B1 or 2 specificity when it comes to the naming of B-blockers?
If the letter starts with A-N = B1 specific
If it’s anywhere from P on, it’s B1=B2.
What is the B-blocker with the shortest duration of action?
What is it used for?
How is it administered?
Esmolol
15 minute diration
IV administered for hour by hour BP control.
Which B-blockers are membrane stabilizers and how do they do this?
Because they stabilize the membrane, what other condition can they be used for?
Mnemonic: PRO rACE CAR driver
Propranolol
Acebutolol
Carvedilol
They block the fast Na+ channels of myocytes and slow down the action potential.
The MOA of these drugs means they can also be used as ANTIARRHYTHMICS.
By what route are most B-blockers administered? What’s the exception?
Orally, except for Esmolol , which is IV admin.
It’s T/2 is so short you can use it for hour by hour control of HTN.
Which B-blockers have Intrinsic Sympathomimetic Activity? (AKA, are partial agonists for B-receptors)
What type of drug reactivity does this help eliminate?
Pindolol
Acebutolol
Carteolol
These drugs physically block Epinephrine from binding B-receptors, while slightly activating them, themselves. They prevent EXCESSIVE activation of B-receptors, while maintaining a little of their physiological activity.
This slight activation prevents the adverse effects of completely blocking B-receptors:
- Bradychardia
- Negative Inotropy (decreased contractility)
What 2 extended actions does Carteolol have?
Slight B-agonism
NO production = vasodilatory effects
Which 2 B-blockers are also partial A-receptor agonists? What does this extended action help prevent?
Carvedilol
Labetalol
When first starting a B blocker, vessels can try to compensate for the resulting slowed heart rate and vasodilation by reflex compensation mechanisms.
This is accomplished normally by a-receptor activation, which constricts the peripheral blood vessels, and negates the effect of the B-blocker.
Carvedilol and Labetolol eliminate this compensatory mechanism.
What B-blocker has antioxidant activity?
Carvedilol
Carvedilol has 3 extended actions:
- Antioxidant generation
- Membrane stabilization - via fast Na+ channel blockade
- Partial alpha agonist - prevents the compensatory increase in TPR after B-blockade
Why should you step-down doses and restrict exercise when coming off a B-blocker?
Sudden systemic elimination of B-blocker effects will cause a sympathetic surge. Your body has responded to the B-receptor blockade by up regulating B-receptors. This causes tachycardia, angina, and sometimes sudden death when sympathetic stimulation is no longer inhibited.
Patients with ___________________ should not take B-blockers. (multiple conditions)
- Congestive Heart Failure. –> These people need all the sympathetic stimulation they can get to maintain their cardiac output.
- People with Conduction Defects/ or are on anti-arrhythmics –> B-blocker use causes bradycardia and bradyarrhythmia
(Verapamil is the anti-arrhythmic he gave us in the ppt. If you’re on it, avoid B-blockers)
- Athsmatics –> B-2 receptor blockade can kill them if they are already bronchoconstricted. It won’t allow them to get air!
- Diabetics: B-blockers take away the means to control blood glucose level (gluconeogenesis/glycogenolysis) and the means to detect low sugar levels (tachycardia).
THIS IS ONLY SEEN IN NONSPECIFIC B-BLOCKERS –> you can use a B1 specific.
Which of the following B-blockers possesses a cardiac-specific effect?
A. Atenolol
B. Pindolol
C. Propranolol
D. Timolol
Atenolol
Remember: Any B blocker that starts with P, on, has equal B1 and B2 effects.
B1 specifics start with A-N.
Which of the following is least likely in a patient who suddenly stops long term use of B-blockers?
A. Angina B. MI C. Tachycardia D. Orthostatic Hypotension E. Sudden death
D. Orthostatic Hypotension.
Which one of these drugs would also be applicable to a man who suffers from Benign Prostatic Hyperplasia? A. Atenolol B. Prazocin C. Clonidine D. Trimethaphan
WHY??
B. Prazocin (Alpha blocker)
Most of the autonomic receptors in the prostate are A1 receptors. Blocking them causes relaxation of the bladder and prostate muscles, relieving the pain.
Do beta blockers cause Na+ and water retention?
NOPE. They work simultaneously in the heart (reduce HR, contractility, and thus, CO) AND KIDNEYS (prevent Renin release).
B1 receptors are in kidneys.
You don’t have to administer a diuretic with them, but their effect of decreasing HTN are additive if you do.
When is a diuretic indicated?
Diuretics are indicated in low to normal renin HTN cases. In high-renin HTN cases, you just need to give a B-blocker, because it will stop renin release via B1 receptor blockade in the Kidneys
What is (according to Dr. Bahouth) one of the most effective drug combo for HTN?
B-blocker and a diuretic
Which B-blocker is available as an eye drop?
Timolol - treats glaucoma
Name the 3rd generation B-blockers and their extra activities.
Labetalol - Nonselective B and A1 receptor antagonist
(Given in HTN emergencies)
Carvedilol - Nonselective B and A1 receptor antagonist,
AND antioxidant effects
Nebivolol - highly B1 selective, with NO-mediated vasodilation