Sympatholytic

Key takeaways

Sympatholytic belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sympatholytic to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sympatholytic from memory before moving on to harder problems.

Reference excerpt

A sympatholytic (sympathoplegic) drug is a medication that reduces activity of the sympathetic nervous system (SNS). They are indicated for various conditions; for example, they may be used to treat high blood pressure. They are also used to treat anxiety, such as generalized anxiety disorder, panic disorder and PTSD. In some cases, such as with guanfacine, they have also shown to be beneficial in the treatment of ADHD.

Mechanisms of action Antiadrenergic agents inhibit the signals of epinephrine and norepinephrine. They are primarily postsynaptic adrenergic receptor antagonists (alpha and beta adrenergic receptor antagonists, or "blockers"), inhibiting the downstream cellular signaling pathways of adrenergic receptors. However, there are exceptions: guanfacine and clonidine are adrenergic agonists at the α2 receptor; since this receptor is located presynaptically, agonism at this receptor inhibits the presynaptic release of adrenaline and noradrenaline, preventing postsynaptic adrenergic receptor activation and downstream signaling. Another way to inhibit adrenergic receptor signaling is by blocking the synthesis of catecholamines. Methyltyrosine, for example, inhibits one of the key enzymes in the pathway: tyrosine hydroxylase. For neurotransmitters to be released, they first must be stored in synaptic vesicles. Reserpine works by inhibiting VMAT, preventing the storage of neurotransmitters into synaptic vesicles. If VMAT is inhibited, neurotransmitters won't be released into the synaptic cleft, thereby inhibiting their downstream effect. Other drugs are preferentially toxic to sympathetic neurons. One method of obtaining such specificity is to exploit drugs that are substrates for a transporter preferentially expressed on sympathetic terminals, such as the norepinephrine transporter. Such transports allows the drugs to accumulate within sympathetic neurones, where they can act to inhibit sympathetic function. Such drugs include bretylium, guanethidine and 6-hydroxydopamine.

Medical uses

Hypertension Many antiadrenergic agents used as antihypertensives include:

Centrally acting Prazosin (α1 inverse agonist) Rescinnamine (ACE inhibitor) Reserpine (VMAT inhibitor) Rilmenidine (imidazoline receptor agonist) Ganglion-blocking Mecamylamine (α3β4 nicotinic receptor antagonist) Trimethaphan (ganglion type receptor antagonist) Peripherally acting Guanethidine (Magnesium-ATPase inhibitor) Indoramin (α1 antagonist) Doxazosin (alpha blocker) Beta blockers Non-selective agents Alprenolol Bucindolol Carteolol Carvedilol (has additional α-blocking activity) Labetalol (has additional α-blocking activity) Nadolol Penbutolol (has intrinsic sympathomimetic activity) Pindolol (has intrinsic sympathomimetic activity) Propranolol Sotalol Timolol β1-selective agents Acebutolol (has intrinsic sympathomimetic activity) Atenolol Betaxolol Bisoprolol Celiprolol Esmolol Metoprolol Nebivolol β2-selective agents Butaxamine (weak α-adrenergic agonist activity) - No common clinical applications, but used in experiments. ICI-118,551 Highly selective β2-adrenergic receptor antagonist - No known clinical applications, but used in experiments due to its strong receptor specificity.

Anxiety

Beta blockers There is clear evidence from many controlled trials in the past 25 years that beta blockers are effective in anxiety disorders, though the mechanism of action is not known. Some people have used beta blockers for performance type social anxiety, or "stage fright." In particular, musicians, public speakers, actors, and professional dancers, have been known to use beta blockers to avoid stage fright and tremor during public performance and especially auditions. The physiological symptoms of the fight/flight response associated with performance anxiety and panic (pounding heart, cold/clammy hands, increased respiration, sweating, etc.) are significantly reduced, thus enabling anxious individuals to concentrate on the task at hand. Stutterers also use beta blockers to avoid fight/flight responses, hence reducing the tendency to stutter. Since they promote a lower heart rate and reduce tremor, beta blockers have been used by some Olympic marksmen to enhance performance, though beta blockers are banned by the International Olympic Committee (IOC). Although they have no recognizable benefit to most sports, it is acknowledged that they are beneficial to sports such as archery and shooting. A recent, high-profile transgression took place in the 2008 Summer Olympics, where 50 meter pistol silver medalist and 10 meter air pistol bronze medalist Kim Jong-su tested positive for propranolol and was stripped of his medal. Posttraumatic stress disorder (PTSD) is theorized to be the result of neurological patterns caused by adrenaline and fear in the brain. By administering beta blockers which can cross the blood brain barrier immediately following a traumatic event, as well as over the next couple weeks, the formation of PTSD has been reduced in clinical studies.

Alpha2 adrenergic agonist Alpha2 adrenergic agonists can also be used to treat anxiety and panic, such as generalized anxiety disorder, panic disorder, or PTSD. Alpha2-adrenergic receptor agonists, such as clonidine and guanfacine, act at noradrenergic autoreceptors to inhibit the firing of cells in the locus ceruleus, effectively reducing the release of brain norepinephrine. Clonidine has shown promise among patients with anxiety, panic and PTSD in clinical trials and was used to treat severely and chronically abused and neglected preschool children. It improved disturbed behavior by reducing aggression, impulsivity, emotional outbursts, and oppositionality. Insomnia and nightmares were also reported to be reduced. Kinzie and Leung prescribed the combination of clonidine and imipramine to severely traumatized Cambodian refugees with anxiety, panic and PTSD. Global symptoms of PTSD were reduced among sixty-six percent and nightmares among seventy-seven percent. Guanfacine produces less sedation than clonidine and thus may be better tolerated. Guanfacine reduced the trauma-related nightmares.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Sympatholytic

Start with the simplest possible case. Write down what Sympatholytic claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sympatholytic before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sympatholytic ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sympatholytic

In research: Sympatholytic appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sympatholytic in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sympatholytic is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antihypertensive agents, so understanding it makes those chapters shorter.
In everyday life: Look for Sympatholytic outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Sympatholytic in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sympatholytic means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sympatholytic out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sympatholytic in simple terms?

A sympatholytic (sympathoplegic) drug is a medication that reduces activity of the sympathetic nervous system (SNS). They are indicated for various conditions; for example, they may be used to treat high blood pressure.

Why does Sympatholytic matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sympatholytic?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sympatholytic.