Types of alpha adrenergic receptors.pptx

Types of alpha adrenergic receptors.pptx

1. TYPES OF ADRENERGIC RECEPTORS ( α - RECEPTORS ) DR. SAURABH KRISHNA VERMA JUNIOR RESIDENT-1 DEPT. OF PHARMACOLOGY AND THERAPEUTICS K.G.M.U. LKO.

2. CONTENT Introduction to Adrenergic Receptors Overview of Alpha Receptors Distribution of Alpha Receptors in the Body Physiological Effects of Alpha Receptor Activation Different Types of Alpha Receptors Mechanism of Action of Alpha-1 Receptors Mechanism of Action of Alpha-2 Receptors Alpha Agonists and Antagonists Clinical Applications and Implications References Questions

3. INTRODUCTION TO ADRENERGIC RECEPTORS Adrenergic receptors are a class of G protein-coupled receptors (GPCRs). These receptors play a crucial role in mediating the effects of the neurotransmitter and hormone adrenaline (also known as epinephrine) and its related compounds, such as norepinephrine (noradrenaline). These receptors are an integral part of the sympathetic nervous system, which is responsible for the body's "fight or flight" response to stress and danger

4. Overview of Alpha Receptors Alpha receptors are a class of adrenergic receptors found in various tissues and cells throughout the body. Norepinephrine (noradrenaline) and epinephrine (adrenaline), both of which are components of the signaling pathway of the sympathetic nervous system, are the primary neurotransmitters that activate these receptors. Alpha receptors play a crucial role in regulating physiological responses to stress, as well as in controlling various functions within the body.

5. Distribution of Alpha Receptors in the Body Alpha-1 Receptors located primarily in the walls of blood vessels and smooth muscles. Alpha-1 receptors play an important role in the regulation of blood pressure, pupil dilation, and metabolism. Alpha-2 Receptors found in both the central and peripheral nervous system.

6. Alpha-2 receptors modulate the release of neurotransmitters and hormones, and are involved in pain reduction, blood sugar regulation, and platelet aggregation. Alpha receptors are distributed throughout the body, but the specific distribution of each subtype varies depending on the tissue and organ.

7. Physiological Effects of Alpha Receptor Activation Alpha-1 Receptors Activation of alpha-1 receptors causes vasoconstriction, which leads to an increase in blood pressure and a reduction in blood flow to non-essential organs. This can also result in pupil dilation, increased sweating, and reduced salivary gland secretion. In addition, alpha-1 activation increases the release of glucose from the liver and triggers contraction in smooth muscles.

8. Alpha-2 Receptors Activation of alpha-2 receptors leads to inhibition of neurotransmitter and hormone release in the central and peripheral nervous systems, resulting in decreased- a) Blood pressure b) Decreased heart rate c) Reduced anxiety. Alpha-2 activation also inhibits insulin secretion and promotes platelet aggregation.

9. Different Types of Alpha Receptors .

10. Subtypes of Alpha receptors α 1 receptors α 1A, α 1B, α 1D : Gq CR α 2 receptors α 2A, α 2B, α2 C : Gi/Go CR

11. α 1 Receptors ( Gq CR) Tissue Localization Predominant Effects α 1A Heart, Liver, Smooth muscle, Blood vessels, Lungs, Vas deferens, Prostate, Cerebellum, Cortex, Hippocampus Contraction of Vascular Smooth Muscles, Promotes cardiac growth & Structure, Vasoconstriction of large resistant arterioles in skeletal muscle. α 1B Kidney, Spleen, Lung, Blood vessels, Cortex, Brainstem Most abundant subtype in heart Promotes cardiac growth and structure α 1D Platelets, Prostate, Aorta, Coronary artery, Cortex, Hippocampus Predominant receptor causing vasoconstriction in Aorta & Coronary arteries

12. α 2 Receptors (Gi/Go CR) Tissue Localization Predominant Effects α 2A Platelets, Sympathetic neurons, Autonomic Ganglia, Pancreas, Coronary/ CNS Vessels, Locus coeruleus, Brainstem, Spinal cord Predominant inhibitory receptor on sympathetic neurons Vasoconstriction of small precapillary vessels on skeletal muscles α 2B Liver, Kidney, Blood Vessels, Coronary/ CNS Vessels, Diencephalon, Pancreas, Platelets Predominant receptor mediating α 2 vasoconstriction α 2c Basal ganglia, Cortex, Cerebellum, Hippocampus Predominant receptor modulating dopamine neurotransmission Predominant receptor inhibiting hormone release from adrenal medulla

13. Mechanism of Action of Alpha-1 Receptors First Messenger Signaling Epinephrine and norepinephrine bind to alpha-1 receptors on the cell surface, activating the receptor and triggering the release of Calcium ions from intracellular stores. Second Messenger Signaling Calcium ions then bind to calmodulin, a calcium-binding protein, which activates a series of protein kinases and signaling molecules, leading to increased myosin ATPase activity and vasoconstriction in smooth muscles, among other effects.

14. Mechanism of Action of Alpha-2 Receptors Presynaptic Alpha-2 Receptors Activation of presynaptic alpha-2 receptors on the terminals of norepinephrine-containing neurons inhibits further release of norepinephrine, thus reducing sympathetic tone and blood pressure. Postsynaptic Alpha-2 Receptors Activation of postsynaptic alpha-2 receptors in the brain leads to sedation, analgesia, and reduced sympathetic outflow, while activation of alpha-2 receptors in peripheral tissues inhibits insulin secretion and promotes platelet aggregation.

15. How Do Alpha Agonists and Antagonists Work? Alpha Agonists They stimulate alpha receptors in the muscles surrounding blood vessels and cause constriction of blood vessels, which leads to an increase in blood pressure . Alpha Antagonists They block alpha receptors in the muscles surrounding blood vessels and cause dilation of blood vessels, which leads to a decrease in blood pressure.

16. Examples of Alpha Agonists and Antagonists Phenylephrine An alpha agonist that constricts blood vessels, reducing nasal congestion and raising blood pressure. Dobutamine An alpha agonist that increases heart rate and contractility, improving heart function in people with heart failure.

17. Doxazosin An alpha antagonist that relaxes muscles in the bladder and prostate, used to reduce high blood pressure and symptoms of benign prostatic hyperplasia . Yohimbine An alpha antagonist used to improve sexual function in men, promote weight loss, and increase energy levels.

18. Clinical Applications and Implications Clinical Application Alpha Receptor Antagonist Cardiac Arrest Epinephrine, a nonspecific alpha and beta agonist, is used in cardiac arrest to stimulate cardiac output and peripheral vasoconstriction. Hypertension Alpha-1 selective antagonists are used to reduce blood pressure by blocking vasoconstriction. Migraine Alpha-2 receptor agonists such as clonidine and tizanidine are used to treat migraines by reducing sympathetic tone and promoting vasodilation.

19. REFERENCES Tripathi, K. D. 8th ed Essentials of medical pharmacology ; New Delhi, India: Jaypee Brothers Medical. 2018

20. QUESTIONS What are alpha receptors and where are they located in the body? What is the physiological significance of alpha-1 receptors? How do alpha-2 receptors contribute to the regulation of neurotransmitter release? What are the clinical implications of alpha receptor activation? How do alpha receptor antagonists work pharmacologically?

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