Pharmacology of Cardiovascular Drugs

Drugs Affecting the Nervous System

• Module 6 covers drugs that impact the nervous system.

Autonomic Pharmacology

• The nervous system is divided into peripheral and central nervous systems.
• The peripheral system further branches into efferent and afferent divisions.
• The efferent division, including the autonomic system, controls involuntary functions. Its branches involved are the parasympathetic nervous system (PNS) and sympathetic nervous system (SNS). SNS is responsible for "fight or flight" responses, while PNS handles "rest and digest."
• Somatic system, part of the efferent division, handles voluntary functions.
• The enteric nervous system is part of the peripheral nervous system, and controls the intestines.
• The central nervous system connects to the peripheral system through nerves connecting the brain and spinal cord to the rest of the body.

Actions of Sympathetic and Parasympathetic Nervous Systems on Effector Organs

• Sympathetic and parasympathetic responses often oppose each other to maintain homeostasis.
• Effector organs such as the eye, glands, heart, kidney, ureters, bladder, and genitalia respond differently to sympathetic or parasympathetic stimulation.
• Red indicates sympathetic responses, and blue shows parasympathetic responses.

Fight or Flight Response vs. Rest and Digest Stimulus

• Sympathetic output (fight-or-flight) is diffuse, affecting multiple organs simultaneously.
• Parasympathetic output (rest-and-digest) targets specific organs.

Sympathetic vs. Parasympathetic Nervous Systems

• Homeostasis in the autonomic nervous system is dynamic, balancing sympathetic and parasympathetic activities.

Neuron

• Neurons are nerve cells that communicate through synaptic signaling.
• The cell body is the neuron's main part.
• The axon is a long extension that transmits signals.
• Dendrites receive signals.
• Myelin sheaths cover axons for faster signal transmission.
• Neurotransmitters are specialized chemicals released at axon terminals affecting target cells.

Types of Neurotransmitters

• Many neurotransmitters exist, but norepinephrine, epinephrine, acetylcholine, dopamine, serotonin, histamine, glutamate, and GABA are most commonly involved in drug therapies.
• Each neurotransmitter binds to specific receptors.

Cholinergic Transmission

• Acetylcholine (ACh) is the primary neurotransmitter released at autonomic ganglia, in parasympathetic postganglionic synapses, and at the somatic neuromuscular junction, as well as some sympathetic postganglionic responses relating to sweat glands.

Adrenergic Transmission

• Norepinephrine (NE) is the primary neurotransmitter at most sympathetic postganglionic neuron-effector cell synapses in the body, while some exceptions exist, like to sweat glands and possibly some vascular regions of skeletal muscle which respond to acetylcholine,
• Dopamine can act as a vasodilator in some blood vessels.

Motor Fiber Diagram

• ACh releases at many relevant locations.
• Adrenergic responses occur further in effector organs.
• The preganglionic and postganglionic neurons operate using ACh, but differ according to the action or response.

Efferent Organ Responses (Adrenergic and Cholinergic)

• Adrenergic and cholinergic responses differ in their effects on various organs, e.g., heart rate, blood vessel constriction/dilation, and gland secretion.
• Some organs have mixed sympathetic and parasympathetic input, resulting in varied responses depending on the dominant system's activity.

Drugs Affecting the ANS

• Drugs can be agonists or antagonists, impacting sympathetic or parasympathetic activity.

Adrenergic Agonists (Sympathomimetic Drugs)

• Norepinephrine and epinephrine are common sympathomimetic drugs used for their vasoconstrictive effects and in critical situations.
• Albuterol is a beta2-agonist used to dilate bronchi and is often prescribed for asthma.
• Dopamine is a potent sympathomimetic drug used to improve blood pressure.

Adrenergic Antagonists (Sympatholytic Drugs)

• Phentolamine blocks alpha receptors, used when norepinephrine or other sympathetic neurotransmitters leak into tissue.
• Beta blockers treat high blood pressure or cardiac issues and block beta receptors. Selective agents block specifically beta 1 or beta 2 receptors, while non-selective agents block both.

Cholinergic Agonists (Parasympathomimetic Drugs)

• Physostigmine can counteract the effects of atropine or in poisoning. It elevates ACh function.
• ACh agonists affect many involuntary processes.

Cholinergic Antagonists (Parasympatholytic Drugs)

• Atropine is a cholinergic antagonist that increases heart rate, reduces secretions.

CNS Stimulants

• Amphetamines, methamphetamine, dextroamphetamine, methylphenidate, and methylxanthines are CNS stimulants.
• The effects (both good and bad) of these stimulants vary and are specific to the drug in question and the individual response.

Anti-anxiety & Sedative-hypnotic Drugs

• Barbiturates and benzodiazepines are used for sedation, promotion of sleep, and anxiety reduction
• CNS function is decreased with the consumption of these drugs.

Analgesics

• These drugs decrease pain sensation.
• Opioids (e.g., morphine) act on endorphin receptors, including mu and kappa.
• Non-opioids (e.g., aspirin, ibuprofen) inhibit Cox enzymes.
• Acetaminophen does not have peripheral side effects.
• NSAIDs (non-steroidal anti-inflammatory drugs) like ibuprofen and aspirin are used to reduce pain and inflammation.

Anesthetics

• These drugs cause loss of sensation, often consciousness.
• Local anesthetics, lidocaine, affect a specific area, usually accompanied by epinephrine.