Drugs that Affect the Autonomic Nervous System Chapter 16 Drugs that Affect the Autonomic Nervous System Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Learning Objectives Explain the major effects of drugs on the autonomic nervous system. Define the effects of sympathetic stimulation. Give an example of an adrenergic drug. Give an example of an adrenergic blocking agent. Become familiar with the different classes of antihypertensive agents. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Sympathetic and Parasympathetic Systems Autonomic nervous system http://www.bing.com/videos/search?q=drug+effects+on+the+autonomic+system+youtube&qpvt=drug+effects+on+the+autonomic+system+youtube&FORM=VQFRML#view=detail&mid=95BBB740EE890D6A9D4B95BBB740EE890D6A9D4B What is the basic function of the autonomic nervous system? Is the autonomic nervous system under conscious control? Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Major Effects of the Sympathetic and Parasympathetic Systems Sympathetic effects Increase in cardiac rate and output Constriction of blood vessels in skin and viscera Elevation of blood pressure and blood sugar Relaxation of smooth muscle in bronchi Decrease in peristalsis Tightening of sphincters Promotion of urinary retention Dilation of pupils Parasympathetic effects Decrease in cardiac rate and output Dilation of blood vessels in skin and viscera (not pronounced) Lowering of blood pressure Constriction of smooth muscle in bronchi Increase in peristalsis Relaxation of sphincters Decrease in urinary retention Constriction of pupils The sympathetic nervous system is the body’s defense mechanism for emergency situations, whereas the parasympathetic system is concerned with maintaining the body’s “status quo.” Explain the fight or flight response, and identify the system to which it relates. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Autonomic Nervous System Sympathetic system “Fight or flight” Prepares people for emergencies Parasympathetic system “Rest and digest” Maintains normal function Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Autonomic Nervous System Neuron is the functional unit Sensory impulses are transmitted to brain and motor impulses to peripheral tissues Synapse: junction of two neurons Ganglion: group of synapses Preganglionic Postganglionic What are the effects of drugs on the nervous system? Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Autonomic Nervous System Neurotransmitters: chemicals that assist with transfer of nerve impulses Acetylcholine Released at postganglionic endings of both systems Inactivated by enzyme acetylcholinesterase Cells that release acetylcholine called cholinergic Epinephrine and norepinephrine Released at postganglionic sympathetic nerve endings Inactivated by enzyme monoamine oxidase Cells that release epinephrine and norepinephrine called adrenergic Researchers believe that these chemicals exist in the tissues and are activated or released by an impulse carried along the nerve. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Sympathetic and Parasympathetic Systems Autonomic Nervous System http://www.bing.com/videos/search?q=myelin+sheath&qs=OS&sk=AS1&FORM=QBVR&pq=mylan%20sh&sc=8-8&sp=2&qs=OS&sk=AS1#view=detail&mid=86D42B9F049D9E0D093E86D42B9F049D9E0D093E For the most part, the actions of the autonomic nervous system are involuntary. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Junction of Two Neurons The neurotransmitters are released into the synapse and travel to the next neuron. When the neurotransmitter reaches that neuron, it stimulates it to release a neurotransmitter into the next synapse. Eventually, the nerve impulse reaches the target organ (e.g., heart, lungs). Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Sympathetic and Parasympathetic Systems Drugs can act in four ways on the autonomic nervous system: Stimulate the sympathetic nervous system Inhibit the sympathetic nervous system Stimulate the parasympathetic nervous system Inhibit the parasympathetic nervous system What is the enzyme that inactivates acetylcholine? What is the enzyme that inactivates epinephrine? How does epinephrine elevate the blood pressure? How does acetylcholine decrease the blood pressure? Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Sympathomimetic (Adrenergic) Agents Epinephrine hydrochloride (Adrenalin, Epi-Pen) Therapeutic uses As vasoconstrictor in eye and nasal mucosa To treat acute bronchial asthma and severe allergic reactions As a heart stimulant for heart block or acute heart failure Very potent drug, dose carefully What are some other Adrenergic agents, and what do they do? Why would epinephrine be useful for treating asthma? Over-the-counter products can also act as vasoconstricting agents in the nasal mucosa. They are called decongestants. When large doses are given, cardiac dilation, pulmonary edema, and cerebrovascular accident may occur. Death may also result from ventricular fibrillation as a result of overstimulation of the myocardium. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Sympatholytic (Adrenergic Blocking) Agents Adrenergic blocking agents nullify the effect of stimulation of the sympathetic nervous system. The net result is similar to stimulation of parasympathetic nervous system. What other types of Adrenergic Blocking agents are there and what do they do and what are they used for? What happens if the beta receptors in the heart are blocked? The decrease in heart rate and cardiac output is more powerful than the alpha stimulation, so beta-blocking agents lower blood pressure. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Ergot Alkaloids Classified as sympatholytic agents All are used in obstetrics except ergotamine Ergotamine tartrate (Gynergen) Constricts cerebral blood vessels Treats migraine headaches Ergonovine Stimulates uterine contractions Notice similarity in drug names. Do not confuse the drugs! Dangerous side effects can accompany prolonged use of ergotamine, as well as when the drug is used too frequently. Over a period of time the constriction of the blood vessels in the toes, fingers, hands, and feet causes gangrene, resulting in death of the tissues and loss of the affected body parts. Constriction of the vessels in the retina of the eye may cause blindness. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Parasympathomimetic (Cholinergic) Agents What are they? What do they do? And what are some examples? What is the name for the receptors that are stimulated by acetylcholine? Neostigmine only acts on peripheral receptors. Physostigmine acts on central and peripheral receptors. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Parasympatholytic (Cholinergic Blocking) Agents What do they do? What are some examples? How are they used? Other parasympatholytic agents include propantheline and combination drugs. Parasympathomimetic drugs are the antidote to overdose poisoning from belladonna drugs. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Neuromuscular Blocking Agents Provide short-term muscle relaxation for endoscopic surgical or endotracheal procedures Examples: Pancuronium bromide (Pavulon) Nondepolarizing, short-term skeletal muscle relaxant Produces paralysis These drugs act at the neuromuscular junction. This is the junction between the terminal nerve ending and the muscle. They block the effect of acetylcholine on the muscle’s receptor (pancuronium, vecuronium) or prevent the muscle from responding to acetylcholine. These drugs cause temporary paralysis, especially of the respiratory muscles. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.

Neuromuscular Blocking Agents Examples: Vecuronium bromide (Norcuron) Similar in action and indications to pancuronium Succinylcholine chloride (Anectine, Quelicin) Drug of choice for orthopedic manipulations and electroconvulsive therapy Very short acting Choice for procedures lasting less than 3 minutes Pancuronium bromide and vecuronium bromide provide short-term skeletal muscle relaxation. Copyright © 2012, 2009, 2005 by Saunders, an imprint of Elsevier Inc. All rights reserved.