L13, 14, 15 Adrenergic Receptor Agonists and Antagonists Flashcards
The sympathetic system is the ___ division of the ANS; the parasympathetic system is the ___ division of the ANS.
Thoracolumbar; craniosacral
The sympathetic system has ___ arms, ___ fingers the parasymapthetic system has ___ arms, ___ fingers.
Short; long
Long; short
Describe the exception of the adrenal gland.
Pre-ganglionic fibers project to the adrenal gland; ACh is released, which activates chromathin cells to produce NE/E. The hormones are released directly into circulation. There is no post-ganglionic nerve fiber
Pre-ganglionic fibers release ___.
ACh
Post-ganglionic parasympathetic fibers release ___.
ACh
Post-ganglionic sympathetic fibers release ___. What is the exception to this?
NE; sympathetic fibers innervating sweat glands and some skeletal muscle blood vessels release ACh
The adrenal gland releases ___ and ___.
NE and EPI
True or false - some organs receive dual ANS innervation and some do not.
True
Describe the effects of the parasympathetic system on the following organs: eye, heart, bronchioles, GI tract, bladder
Eye: pupillary constriction (miosis), accommodation
Heart: negative chronotropy (bradycardia)
Bronchioles: constriction of smooth muscle
GI tract: increased motility, secretions
Bladder: stimulates emptying
Describe the effects of the sympathetic system on the following organs/functions: eye, heart, bronchioles, blood vessels, GI tract, bladder, metabolic functions
Eye: pupillary dilation (mydriasis)
Heart: increased chronotropy and inotropy
Bronchioles: smooth muscle relaxation
Blood vessels: constriction or relaxation
GI: decreased motility
Bladder: inhibits emptying
Metabolic functions: increased blood sugar
Parasympathetic innervation of the eye leads to constriction of the ___, causing miosis, and constriction of the ___, leading to accommodation.
Sphincter muscles of the pupil; ciliary muscles
Parasympathetic innervation of the heart reduces heart rate via the ___ and reduces conduction via the ___.
SA node; AV node
Parasympathetic innervation of the bladder leads to contraction of the ___, causing bladder emptying.
Detrusor muscle
Sympathetic innervation of the eye leads to constriction of the ___, causing mydriasis, and activation of the ___, leading to production of aqueous humor.
Dilator muscle; ciliary epithelium
Sympathetic innervation of the heart increases heart rate via what process?
Accelerated SA node pacemaker depolarization
What are the three main currents that contribute to SA node membrane potential?
- Inward calcium current
- Funny current
- Outward potassium current
How does sympathetic innervation accelerate SA node pacemaker depolarization?
Increases inward calcium current and funny current to promote faster phase 4 depolarization and lower the threshold for activation; it also stimulates increased calcium influx into myocytes, leading to greater contractile force
Upon what two variables does the outcome of sympathetic innervation of blood vessels depend?
- Relative density of receptor population (alpha1 vs. beta2) in the targeted vascular bed
- Ligand available to mediate the vascular response (NE vs. E)
Sympathetic innervation of the bladder leads to contraction of the ___ and relaxation of the ___, leading to inhibition of emptying.
Urethral sphincters; detrusor muscle
What are the 5 broad steps of adrenergic neurotransmission?
- Synthesis
- Storage in vesicles
- Release of catecholamines
- Binding of NT to post- or pre-synaptic sites
- Termination of action
What happens during synthesis of adrenergic NT?
Tyrosine hydroxylase (rate-limiting enzyme) converts tyrosine to DOPA. DOPA is metabolized to DA. Half of DA is transported into vesicles via VMAT (the other half is metabolized)
What happens during vesicle storage of adrenergic NT?
Dopamine can be converted to NE via dopamine beta-hydroxylase. EPI can be produced from NE via phenylethanolamine-N-methyltransferase. EPI and NE are also produced in the adrenal medulla.
What happens during release of catecholamines?
Voltage dependent opening of calcium channels elevates intracellular calcium and stimulates the interaction of SNARE proteins to enable vesicle fusion and exocytosis of the vesicle contents
The action of a NT depends upon what three things?
- Receptor type
- Second messenger system
- Machinery of the cell type
What are the three mechanisms of termination of action?
- Re-uptake into nerve terminals or post-synaptic cell
- Diffusion out of synaptic cleft
- Metabolic transformation
Where are alpha1 receptors located?
- Most vascular smooth muscle*
- Pupillary dilator muscle*
- Pilomotor smooth muscle
Where are alpha2 receptors located?
- Adrenergic and cholinergic nerve terminals*
- Platelets
- Some vascular smooth muscle
Where are beta1 receptors located?
- Heart*
2. Juxtaglomerular cells*
Where are beta2 receptors located?
- Respiratory, uterine, and vascular smooth muscle*
- Liver*
- Pancreatic beta cells
- Somatic motor nerve terminals (voluntary muscle)*
Where are beta3 receptors located?
- Fat cells
Where are dopamine1 receptors located?
- Renal and other splanchnic blood vessels*
Where are dopamine2 receptors located?
1.Nerve terminals
What are the effects of binding alpha1 receptors?
- Contraction of vascular smooth muscle*
- Contraction of pupillary dilator muscle (mydriasis)*
- Contraction of pilomotor smooth muscle (erects hair)
What are the effects of binding alpha2 receptors?
- Inhibition of NT release at adrenergic and cholinergic nerve terminals*
- Stimulates aggregation of platelets
- Contracts some vascular smooth muscle
What are the effects of binding beta1 receptors?
- Stimulates increased rate and force of heart*
2. Stimulates renin release from juxtaglomerular cells*
What are the effects of binding beta2 receptors?
- Relaxation of respiratory, uterine, and vascular smooth muscle*
- Stimulates glycogenolysis in the liver*
- Stimulates insulin release from pancreatic beta cells
- Causes a tremor via somatic motor nerve terminals*
What are the effects of binding beta3 receptors?
- Stimulates lipolysis in fat cells
What are the effects of binding dopamine1 receptors?
- Relaxes (reduces resistance) renal and other splanchnic blood vessels*
What are the effects of binding dopamine2 receptors?
- Inhibits adenylyl cyclase at nerve terminals
Alpha1 adrenergic receptors are positively coupled to ___ via which G-protein?
PLC; G-alpha-q
Describe what happens in vascular smooth muscle when an agonist binds to an alpha1 adrenergic receptor.
- Agonist binds receptor
- G-alpha-q subunit activates PLC
- PLC liberates IP3 and DAG
- IP3 activates an IP3 receptor that acts as a calcium release channel in the SR
- Calcium is released into the intracellular space, increasing [Ca2] and stimulating smooth muscle contraction
Alpha2 adrenergic receptors are negatively coupled to ___ via which G-protein?
Adenylyl cyclase; G-alpha-i subunit
Describe what happens at an adrenergic nerve terminal when an agonist binds to an alpha2 adrenergic receptor.
- Agonist binds to alpha-2 receptor
- G-alpha-i inhibits adenylyl cyclase
- This reduces cAMP, which reduces activation of PKA
- Phosphorylation of N-type calcium channels on nerve terminals is reduced, reducing calcium influx during membrane depolarization and reducing vesicular release of NT
Beta1 adrenergic receptors are positively coupled to ___ via which G-protein?
Adenylyl cyclase; G-alpha-s
Describe what happens in a cardiac pacemaker cell when an agonist binds to an beta1 adrenergic receptor.
- Agonist binds beta1 receptor
- G-alpha-s activates adenylyl cyclase
- Adenylyl cyclase produces cAMP
- cAMP activates PKA
- PKA phosphorylates Ca2+ channels in the membrane of SA node cells, leading to increased slow inward calcium current and faster nodal cell depolarization
- cAMP also directly activates funny currents to increase the slope of depolarization
Describe what happens in a cardiac myocyte cell when an agonist binds to an beta1 adrenergic receptor.
- Agonist binds beta1 receptor
- G-alpha-s activates adenylyl cyclase
- Adenylyl cyclase produces cAMP
- cAMP activates PKA
- PKA phosphorylates L-type calcium channels in myocyte membranes, leading to enhanced calcium influx and larger trigger signals for release of Ca2+ from the SR. Trigger calcium also enters the SR, increasing storage so that the next trigger initiates larger efflux of calcium.
Beta2 adrenergic receptors are positively coupled to ___ via which G-protein?
Adenylyl cyclase; G-alpha-s
Describe what happens in vascular smooth muscle when an agonist binds to an beta2 adrenergic receptor.
- Agonist binds beta1 receptor
- G-alpha-s activates adenylyl cyclase
- Adenylyl cyclase produces cAMP
- cAMP activates PKA
- PKA phosphorylates and INHIBITS MLCK. This prevents actin and myosin from interacting/muscle from contracting. This phosphorylation also reduces the affinity of MLCK for Ca-calmodulin, resulting in further reduction.
Describe what happens in vascular smooth muscle when an agonist binds to an alpha2 adrenergic receptor.
Peripheral vasoconstriction through the opposite mechanism of beta-adrenergic receptors.
What are the two categories of adrenomimetic agnoists?
- Direct-acting
2. Indirect-acting
What are the 2 categories of indirect-acting adrenomimetic agonists?
- Releasers
2. Reuptake inhibitors
What are the 2 categories of direct-acting adrenomimetic agonists?
- Alpha agonists
2. Beta agonists
What are the 3 categories of alpha agonists?
- Nonselective
- Alpha-1 selective
- Alpha-2 selective
What are the 3 categories of beta agonists?
- Nonselective
- Beta-1 selective
- Beta-2 selective
What are the 3 endogenous ligands for adrenergic receptors?
NE, EPI, DA
MAP = ? CO = ?
CO*TPR
HR * SV