Pharmacology - ANS: Cholinergic and Adrenergic drugs

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ACh

What is the neurotransmitter at the following sites?
- parasympathetic synapses: both pre and postganglionic
- preganglionic sympathetic synapses
- neuromuscular junction (in the somatic nervous system)
- some synapses of the brain

cholinergic

__________________ drugs can be divided into: cholinergic stimulants and anticholinergic

agonists

Cholinergic stimulants work as __________________

antagonists/blockers

Anticholinergic drugs work as ________________

cholinergic

The two major types of _____________ receptors are: muscarinic and nicotinic

organs

Muscarinic receptors are mainly found on __________

somatic muscle, jct. of a preganglionic neuron

Nicotinic receptors are mainly located on ____________

cholinergic receptors

- two major types
- located on the postsynaptic membranes and on the surface effector cells

specific, all

The existence of different varieties of cholinergic receptors is important pharmacologically b/c: some drugs are relatively ___________ for certain receptor subtypes while others bind indiscriminately to __________ cholinergic receptors

stimulants

Cholinergic ______________ are either direct-acting or indirect-acting.

direct-acting

_______________ cholinergic stimulants bind directly to the cholinergic receptor and activate the receptor, which in turn activates the cellular response.

direct-acting cholinergic stimulants

- are true cholinergic agonists (they function just as ACh)
- those that are specific to muscarinic receptors are more beneficial b/c they act at the peripheral tissues
- causes classic parasympathetic response, but unchecked can be very damagin
- helps secrete digestive juices

indirect-acting

__________________ cholinergic stimulants increase activity at the cholinergic synapses by inhibiting acetylcholinesterase agents.

indirect-acting cholinergic stimulants

- not specific to muscarinic receptors only so the stimulate all cholinergic receptors (parasympathetic synapses; both pre- and postganglionic, preganglionic sympathetic synapses, neuromuscular junction [in the somatic nervous system] and some synapses of the brain
- they are capable of global effects

Alzheimer's disease

(clinical application of cholinergic stimulants) - cholinesterase inhibitors stimulate the cells that are still functional in the cerebral cortex

GI and urinary bladder anatomy

(clinical application of cholinergic stimulants) - trauma to the viscera can cause temporary atony in the smooth muscles, so peristalsis in the intestine and urinary retention can also occur. So, a cholinergic stimulant can be given until normal function returns

Glaucoma

(clinical application of cholinergic stimulants) - _____________ results from an increase in aqueous humor within the eyeball. Normally the parasympathetic nerve supply stimulates aqueous humor outflow. Cholinergic agonists can be administered locally to a patient suffering with ___________ to reduce interocular pressure.

Myasthenia gravis

(clinical application of cholinergic stimulants) - a disease characterized by skeletal muscle weakness caused by autoimmune destruction of the cholinergic postsynaptic receptors at the neuromuscular junction. A cholinesterase inhibitor allows ACh to hang around the neuromuscular junction. A cholinesterase inhibitor allows ACh to hang around the neuromuscular junction longer to stimulate available receptors.

Reversal of anticholinergic-induced toxicity

(clinical application of cholinergic stimulants) - indirect cholinergic drugs can be used as an antidote for and overdose of an anti-cholinergic drug by inhibiting ACh break down

Reversal of neuromuscular blockage during anesthesia

(clinical application of cholinergic stimulants) - curare is given with anesthesia to block transmission at the NMJ in order to keep the patient motionless (paralyzed) during a surgical procedure. To bring them back out of the anesthesia indirect acting cholinergic stimulants are given to keep the ACh hanging around the NMJ and overcome the paralyzing drug.

Adverse effects of cholinergic (parasympathetic) drugs

- GI distress (nausea, vomiting, diarrhea, abdominal cramping)
- bradycardia
- increased sweating
- flushing 2ndry to vasodilation of peripheral blood vessels

Anti-cholinergic agents

- these drugs act to diminish cholinergic stimulation
- are competitive antagonists of the cholinergic receptors (they bind reversibly to cholinergic receptors but do not activate them)
- are classified as anti-muscarinic or anti-nicotinic

anti-muscarinic

atropine is the classic prototype, used in medicine and in warfare

anti-nicotinic

similar to the drug used to reverse anesthetically induced paralysis

G.I.

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - reverses parasympathetic reactions like gastric secretions and __________ motility (tx. of peptic ulcers and irritable bowel syndrome)

cardiovascular system

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - atropine is used to block the vagus nerve (CN10). So atropine is used to tx bradycardia and/or some arrhythmias

eye

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - used to dilate the pupil (parasympathetic causes constriction so and anti-parasympathetic would cause dilation

cholinergic poisoning

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - certain mushrooms, insecticides and chemical weapons use cholinergic agents. Atropine is used as an antidote

motion sickness

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - blocking parasympathetic stimulation of certain motion-sensitive areas of the brain will alleviate ________________

Parkinson's disease

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - these drugs block the cholinergic receptors in the basal ganglion to reduce the symptoms of this disease

Respiratory tract

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - the vagus nerve unchecked will cause bronchoconstriction. So, anti-cholinergic drugs (cholinergic blockers) will result in bronchodilation

Urinary tract

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - atropine is used to alleviate frequency and incontinence by reducing bladder hypertonicity (like during a UTI)

Pre-op

(Clinical Application of anti-muscarinic drugs (Atropine does all this)) - atropine is used to reduce respiratory tract secretions and bradycardia during anesthesia

Side effects of anti-cholinergic drugs

- systematically administered meds cannot be targeted to one specific organ exclusively (e.g. drugs given for diarrhea will also effect the bladder, respiratory tract, heart and eyes)
- these drugs are associated with a number of side effects (xerostomia (dry mouth), blurred vision, urinary retention, constipation, tachycardia, CNS symptoms [confusion, dizziness, nervousness, drowsiness 2ndary to anti-cholinergic drugs that cross the blood-brain barrier})

norepinephrine

____________________ usually the neurotransmitter at the junction between postganglionic neurons and peripheral tissues

agoinst adrenergic receptor

Adrenergic alpha and beta receptors are classified as ____________________

alpha 1

______________ are agonist adrenergic receptors located on vascular smooth muscle NMIs causing vasoconstriction when stimulated

alpha 2

______________ are agonist adrenergic receptors located at CNS synapses resulting in decreased (inhibit) sympathetic discharge in the brainstem and inhibition of neuronal excitation in the spinal cord when stimulated

beta 1

______________ are agonist adrenergic receptors located on myocardial tissue resulting in increased heart rate and force of contraction when stimulated

beta 2

______________ are agonist adrenergic receptors located on bronchioles resulting in branchodilation and uterus resulting in relaxation when stimulated

selective

An adrenergic drug may be _____________ for a particular receptor but it can also have a lesser affinity for other types of adrenergic receptors (i.e. a beta 1 specific drug can bind preferentially to a beta 1 receptor but may show slight affinity for a beta 2 receptor)

dose

Selectivity may be ______________ related. With higher and higher doses a drug may be more apt to attach to other types of receptors. So, overdosing on an adrenergic drug can cause unwanted side effects because it will stimulate receptors it was not meant to stimulate

Alpha 1 agonists

- cause vasoconstriction and so are Rx'd for acute hypotension (i.e. shock)
- they are also Rx'd for nasal congestion because they are used to decrease HR during paroxysmal supraventricular tachycardia. This occurs because increasing peripheral vascular resistance causes a reflexive decrease in HR via the cardiac baroreceptor reflex (reflexive bradycardia) in the brain stem

Adverse side effects of Alpha 1 agonists

- increased BP
- abnormally low HR due to reflexive bradycardia

Alpha 2 agonists

- these drugs stimulate receptors in the brain/brainstem resulting in INHIBITION of sympathetic discharge from the vasomotor center. Diminished SNS discharge results in decreased BP.
- its receptors are also found in interneurons in the spinal cord. When stimulated these receptors inhibit the interneurons which can result in reduction in muscle spasticity

Adverse side effects of Alpha 2 agonists

- minor dizziness and drowsiness
- major dyspnea and bradycardia

Beta 1 Agonists

- stimulate receptors which are located primarily on myocardial cells. When stimulated they cause increased force and rate of contraction (increased C.O.), stimulation of these receptors can be very useful in emergency situations.
- can be used to treat heart disease (i.e. heart failure)

Adverse side effects of Beta 2 agonists

- nervousness, restlessness, trembling to severe asthmatic attack.
- if used during pregnancy may cause increased HR and BP and pulmonary edema in the mother

Adrenergic antagonists

- what ever adrenaline was supposed to do it can't do
- as you would expect these are blockers that attach to the receptors but do not activate them
- they are also called sympatholytic drugs
- they are relatively selective

Alpha Antagonists

- used primarily to peripheral vascular tone by blocking the alpha 1 receptors. Remember endogenous catecholamines cause vasoconstriction of peripheral blood vessels so blocking these would cause vasodilation
- so these are RX'd for HTN

Adverse side effects of Alpha antagonists

- reflexive tachycardia. As BP drops there is a compensatory increase in HR (remember the baroreceptor reflex?)
- orthostatic hypotension

Beta Antagonists

- generally used to effect the Beta 1 receptors
- cause a decrease in cardiac contractile force and rate = decreased C.O.
- these are used to normalize heart rate in arrhythmias or to reduce cardiac damage after MI

Adverse effects of Beta Antagonists

- with these being nonselective you may get a desired effect at one receptor type but an undesired one at another receptor type. (e.g. decreased HR (desired) but bronchiospasm (undesired)
- they are associated with: depressed cardiac function, orthostatic hypotension, syncope

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