Sympathomimetics Flashcards
What are the five areas of the CNS forming the central autonomic network (CAN)?
- Cerebral cortex (limbic)
- Hypothalamus
- Amygdala
- Spinal cord components
- Medulla and Pons
These areas play crucial roles in regulating autonomic functions.
What is the function of the Nucleus Tractus Solitarius (NTS)?
Relays afferent signals from various receptors to the central autonomic network
It acts as a ‘traffic cop’ for signals from chemoreceptors, baroreceptors, and more.
What is the ratio of pre to post ganglionic neurons in the PNS?
1:1
This indicates a localized and specific effect in the parasympathetic nervous system.
What is the ratio of pre to post ganglionic neurons in the SNS?
1:20
This leads to a mass discharge effect during sympathetic stimulation.
What characterizes the ‘mass discharge’ of the SNS?
A multisystem response due to the 1:20 ratio of pre to post ganglionic neurons
This response is managed by the CHASM part of the CAN.
What type of receptors are used by the alpha, beta, and dopaminergic systems?
G protein receptors
These receptors are activated by ligands such as NE and epinephrine.
What is the primary second messenger activated by Gs receptors?
Cyclic adenosine monophosphate (cAMP)
This is important for signaling pathways in the sympathetic nervous system.
What are the effects of SNS activity on blood pressure?
Increase
This occurs due to increases in heart rate and stroke volume.
What is the primary neurotransmitter produced and stored by chromaffin cells?
Epinephrine
The adrenal medulla produces 80% epinephrine and 20% norepinephrine.
What is the rate limiting step in catecholamine synthesis?
Tyrosine to Dopa
This conversion is crucial for the production of catecholamines.
What enzyme performs O-methylation in neurotransmitter metabolism?
Catechol-O-Methyltransferase (COMT)
This enzyme is involved in the breakdown of catecholamines.
What are sympathomimetics?
Drugs that mimic the effects of stimulation of the sympathetic nervous system
They can act directly on adrenergic receptors or indirectly through other mechanisms.
What is the typical action of direct acting sympathomimetics?
Activate adrenergic receptors directly
Examples include epinephrine and norepinephrine.
What are the side effects of epinephrine?
- Increased glucose
- Restlessness
- Decreased potassium
- Potential for dysrhythmias
- Increased plasma lactate levels
These effects are due to its action on multiple adrenergic receptors.
What is the primary action of norepinephrine?
Vasoconstriction
It primarily acts on alpha-1 receptors to increase systemic vascular resistance.
What is the primary receptor type affected by dopamine at low doses?
D1 and D2
This leads to vasodilation at low doses.
What differentiates isoproterenol from other sympathomimetics?
It is a synthetic catecholamine with strong beta-1 activity
It is primarily used for its inotropic and bronchodilatory effects.
What is the mechanism of action of dobutamine?
Increases cAMP leading to increased contractility
This makes it useful in heart failure and low output states.
What is the primary action of phenylephrine?
Vasoconstriction
It primarily acts on alpha-1 receptors.
What are the receptors associated with vasopressin?
- V1: vascular smooth muscle
- V2: renal distal tubules
- V3: pituitary gland
Each receptor type mediates different physiological effects.
What is reflex bradycardia?
Decreased heart rate due to baroreceptor stimulation
It is part of the physiological response to hypertension.
What is the expected effect of selective B2 sympathomimetics?
Bronchodilation and smooth muscle relaxation
Commonly used in respiratory conditions.
What should be avoided when a patient is taking MAO inhibitors?
Ephedrine
Direct acting agents are preferred in patients on MAO inhibitors.
What do tricyclic antidepressants (TCA) inhibit?
Reuptake of norepinephrine
This increases the availability of norepinephrine in the synaptic cleft.
What is the recommended action regarding Monoamine Oxidase Inhibitors (MAOi) before a procedure?
Keep taking medications
New data suggests that patients should not stop taking MAOi for 2-3 weeks as previously recommended.
What type of agent should be used for adrenergic agonist when a patient is taking MAOi?
DIRECT acting agent
This is important to avoid complications.
Which substance should be avoided when a patient is on MAOi?
EPHEDRINE
Name two examples of Monoamine Oxidase Inhibitors.
- Marplan
- Nardil
What do Tricyclic Antidepressants (TCA) inhibit?
Reuptake of NE back into postganglionic neurons
What should patients do regarding their TCA medications?
Keep taking medications
What type of agent should be used when a patient is on TCA?
DIRECT acting agent
This is the same recommendation as for patients on MAOi.
Name two examples of Tricyclic Antidepressants (TCA).
- Amitriptyline
- Doxepin
True or False: Patients on MAOi should stop their medications for 2-3 weeks before starting a new treatment.
False
What class of medications do Marplan and Nardil belong to?
Monoamine Oxidase Inhibitors (MAOi)
What is the primary action of Tricyclic Antidepressants (TCA)?
Inhibit the reuptake of norepinephrine (NE)
Fill in the blank: The older class of medication that includes Amitriptyline is called _______.
Tricyclic Antidepressants (TCA)
Epi: chronotropic/dromotropic/inotropic/bronchodilitory dose
0.01-0.03 mcg/kg/min (B1 and B2)
Epi: chronotropic/vasoconstrictive dose
0.03-0.15mcg/kg/min (B1 and A1)
Epi: pure vasocontrictive dose
> 0.15mcg/kg/min (A1)
Norepi infusion
0.02-0.4 mcg/kg/min (B1 low dose, more A1 as you increase dose)
Dopamine: vasodilation
0.5-2 mcg/kg/min (D1,D2)
Dopamine: bronchodilitory/chronotropic /vasoconstrictive dose
2-10 mcg/kg/min (B1, B2, A1)
Dopamine: pure vasoconstrictive dose
> 10 mcg/kg/min (A1)
Isuprel
1-5 mcg/min (B1 > B2)
Dobutamine
2-10 mcg/kg/min (B1 > A1, B2)
*more A1 above 5mcg/kg/min
Ephedrine
5-25mg (mostly B1, weak B2, some A1)
Vasopressin
20 units bolus (conc. 20u/ml)
*add 19mlNS to 1ml vasopressin= 1unit/ml
Phenylephrine
50-200 mcg bolus (almost pure A1)
