Beta Receptor Systems Most tissues express multiple receptors. However, the dominant beta receptor in the normal heart is the beta 1 receptor while the beta 2 receptor is the dominant regulatory receptor in vascular and non vascular smooth muscle.
Epinephrine activates both the beta 1 and beta 2 -receptors. Norepinephrine activates only the beta 1 -receptor. Effect of Beta 1 Receptor Activation on the Heart : Activation of the beta 1 receptor leads to increases in contractile force and heart rate.
Drugs that activate the beta 1 receptor can be used in heart failure to improve the contractile state of the failing heart. Drugs that activate the beta 1 receptor also increase heart rate.
Indeed, excess stimulation the beta 1 receptor can induce significant increases in heart rate and arrhythmias. Arrhythmias are a major concern with drugs such as epinephrine that can be absorbed systemically after intra-oral injection. Effect of Beta 2 Receptor Activation on Smooth Muscle: Activation of the beta 2 receptor leads to vascular and nonvascular smooth muscle relaxation.
Drugs that activate the beta 2 receptor can be used to treat as asthma by relaxing airway smooth muscle and premature labor by relaxing uterine smooth muscle. Alpha receptors have been further subdivided into alpha 1 and alpha 2 receptors. Both epinephrine and norepinephrine activates both the alpha 1 and alpha 2 receptors.
Presynaptic Alpha 2 Receptors Alpha 2 receptors also exist presynaptically associated with nerve terminals. Activation of these receptors inhibits the release of norepinephrine. Norepinephrine acts at presynaptic alpha 2 receptors to inhibit its own release.
Postsynaptic Alpha 1 Receptors on Vascular Smooth Muscle: Associated with vascular smooth muscle are a large number of alpha 1 receptors relative to beta 2 receptors. Activation of these receptors by sympathetic nervous system transmission or drugs will result in vasoconstriction and an increase in peripheral resistance and systemic arterial blood pressure.
Applications to Therapeutics Oral dosing of norepinephrine or epinephrine is not possible due to the rapid metabolism of catechol nucleus in gastrointestinal mucosa and liver. Therefore, these agents are given I. Epinephrine is often used in combination local anesthetic agents to prolong the duration of anesthetic action. This would include articaine, bupivacaine or lidocaine.
This combination is used because epinephrine can induce vasoconstriction thus limiting the diffusion of the local anesthetic from the site of injection. This not only prolongs the actions of the local anesthetic but also to reduce the toxicity of the local anesthetic by limiting its systemic absorption.
Lidocaine in toxic doses can produce cardiac arrthythmias and convulsions. Epinephrine can also be topically applied in surgical procedures to induce vasoconstriction and thus reduce blood loss. Epinephrine is used in the treatment of shock and in emergency situations related to bronchial asthma. Clinical studies have shown that epinephrine blood levels increase following its intraoral administration. The risk of this increase is dependent on characteristics of the patient.
For example, hypertensive patients or those with other cardiovascular disease or patients taking other drugs that affect sympathetic nervous system function are at higher risk than patients without these conditions. Systemically absorbed epinephrine could also increase heart rate and exacerbate cardiac rhythm disturbances or myocardial ischemia.
Learning Objectives Lecture II 1. Understand the potential sites of action for sympathomimetics and the difference between a direct and indirect acting agonist. Understand the pharmacologic actions and therapeutic actions of drugs that act at the beta 1 and beta 2 -adrenergic receptors as well as the alpha 1 -adrenergic receptor.
Know the mechanism of action and effects of amphetamine and cocaine. Understand how the pressure of sympathomimetics alters the dental management of patients. Sympathomimetics: synthetic analogs of naturally occurring catecholamines that mimic the actions of the endogenous neurotransmitters.
These agents can be divided into direct and indirect acting sympathomimetics. Direct acting agonists or antagonists can act at postsynaptic receptors.
Indirect acting agonists release neurotransmitters from presynaptic nerve terminals to produce a sympathomimetic effect. Inhibition of the membrane uptake of catecholamines by drugs such as cocaine and tricyclic antidepressants produce a sympathomimetic effect. Inhibition of monoamine oxidase by drugs such as Tranylcypromine.
In congestive heart failure, the failing heart is not able to eject blood as efficiently as the normal heart. As a result there is a decrease in cardiac output which triggers a host of compensatory actions. These include fluid retention, vasoconstriction, an increase in peripheral vascular resistance, an increase in the levels of circulating catecholamines and tissue hypoxia.
Dopamine and dobutamine activate the myocardial beta 1 receptor and thus increase the force of contraction of the failing heart.
This will result in an increase in cardiac output. These drugs are reserved for use in the acute management of heart failure. These agents have a higher affinity lower equilibrium dissociation constant for beta 2 receptors when compared to beta 1.
Therefore, they selectively activate beta 2 receptors when compared to beta 1. Uses 1. Airways dysfunction; bronchial asthma, chronic bronchitis, emphysema In airways dysfunction, beta 2 selective agonists relax airways thus decreasing airways resistance. Premature labor In premature labor, the beta 2 selective agonists relax uterine smooth muscle.
Drugs that relax uterine smooth muscle are referred to as tocolytic agents. Side effects related to dental practice 1. Xerostomia, with inhaler usage. These structural modifications of the parent catecholamine nucleus result in drugs that are orally active and have longer plasma half-lives.
However, these same modifications result in lower affinity for the receptor than do the endogenous agonists epinephrine or norepinephrine. There are two structural classes of alpha 1 agonists phenethylamines which are closely aligned in structure to epinephrine and the imidazolines, compounds structurally unrelated to epinephrine.
Levonordeferin is a phenyethylamine that has been used in dental practice in combination with local anesthetics. Hypotension-to increase blood pressure during a surgical procedure where a general anesthetic has induced hypotension 2.
Ophthalmic preparations-to induce mydrasis also in topical preparations for symptomatic release of eye irritation. Cough and cold preparations-Induces constriction of nasal mucosa decreases resistance to air flow. Indirect Acting Sympathomimetics These agents require the presence of endogenous catecholamines to produce their effects.
They have little activity if catecholamines are depleted. Cocaine: Blocks reuptake of monoamines into nerve endings. Cocaine also has local anesthetic activity. Amphetamine: Promotes the release of NE from nerve endings. Amphetamine can also block the reuptake of norepinephrine. Amphetamine-like compounds 1. Methylphenidate A major site action of cocaine, amphetamine and amphetamine-like agents is in the CNS.
These drugs produce a feeling of well being and euphoria. As a result the drugs carry a significant abuse liability. Both cocaine and amphetamine are on the FDA schedule 2. Uses of Cocaine 1 below , Amphetamine and Amphetamine-like agents below 1. Health conditions other than what you need to treat with an adrenergic drug can play a role in deciding which drug is right for you.
You can discuss all of these factors with your doctor to find a good choice. Epinephrine and norepinephrine sound alike, and they also share many of the same functions.
Learn more about these two hormones and neurotransmitters…. Experts say that people should focus on all the risk factors for heart disease, even if their cholesterol is at acceptable levels. Trying to protect your new mattress from liquids and stains? Check out our picks for the best waterproof mattress protectors for allergies, bedwetting,.
Slow brain waves reveal precisely when a patient loses awareness while under anesthesia, and could prevent the small percentage of cases in which…. Learn more. The vagus nerve is the longest of the 12 cranial nerves. Here, learn about its anatomy, functions, and the kinds of health problems that can occur.
Muscle twitching refers to small muscle contractions in the body. Learn more about the causes and treatment here. Learn more about this and how it relates to autism. Health Conditions Discover Plan Connect.
How they work Types and uses Takeaway What are adrenergic drugs? How they work. Types of adrenergic drugs and their uses. Other considerations. Read this next. Medically reviewed by Dena Westphalen, Pharm. The Best Waterproof Mattress Protectors. Medically reviewed by Kevin Martinez, M. What Causes Numbness in Hands? Medically reviewed by Heidi Moawad, M. What is the Vagus Nerve? Medically reviewed by Seunggu Han, M. Peripheral Neuropathy.
Stimming: Causes and Management. Medically reviewed by Timothy J. Legg, Ph.
0コメント