6 - Sympatholytic Pharmacology Flashcards
Receptor agonists for Sympathetic NS activate what signal transducton cascade (ex. a1 receptor)
Gq -> PLC –> IP3 and DAG
IP3–> Increase Ca++
DAG –> activate Protein Kinase C
Receptor antagonists block ______
agonist binding to the receptor
(antagonize the effect of agonist, not the receptor itself)
What effect would antagonist alone have on receptor activation?
None!
If no agonist, no action
nonselective alpha antagonists
Phenoxybenzamine
Phentolamine
a1 receptor antagonists
Prazosin
Terazosin
Doxazosin
AE’s of a1 antagonists
- Orthostatic HoTN**
- Inhibition of ejaculation
- Nasal congestion
- Reflex tachycardia
Clinical uses for a1/2 receptor antagonists
- Pheo
- Hypertensive crisis
(Phentolamine also used for male impotence)
a1 antagonists are all ____ adminstered except _____
orally
Phentolamine (parrenteral)
____ can be relieved with a1 blockers to cause __________
BPH
bladder base relaxation
Non-selective alpha receptor groups
B haloalkylamines (Phenoxybenzamine)
Imidazolines (phentolamine)
Phenoxybenzamine effects
Also blocks receptors for:
- Ach
- Histamine
- Serotonin
Phenoxybenzamine PD
irreversible antagonist = covalent binding to receptor is permanent
***Therefore very LONG duration
Competitive (reversible) non-selective alpha receptor blocker
Phentolamine
Phentolamine is a _____ but induces ______
potent vasodilator
Induces pronounced reflex tachyardia
Phentolamine also blocks..
5HT receptors
and is a muscarinic and histamine receptor agonist
Phentolamine block of _____ may promote release of NE
presynaptic a2
Components of Quinazolines
Quinazoline ring
Piperazine ring
Acyl moiety
Quinazolines vary in
half life
Praz = 3h
Teraz = 12h
Doxaz = 20h
Quinazolines undergo extensive
metabolism, excreted in bile
Quinazoline effects
Vasodilation
relaxation of sm. muscle in enlarged prostate and in bladder base
Quinazolines exhibit _____
“first dose” effect
Quinazolines are all _______
a1 antagonists
Yohimbe MOA
blocks a2 receptors = increase symptathetic discharge
Aryloxypropanolamines structure
Aromatic ring attached to non-carbon atom in side chain
R group (bulky alkyl group…isopropy or tert-butyl) on a terminal NH group
Aryloxypropanolamines general function
B receptor antagonists
Nonselective B agonists
- Propanolol
- Nadolol
- Timolol
- Pindolol
- Carteolol
Nonselective B antagonists - 2 properties
Lipophilic
Local anesthetic properties
B antagonist blockde is _________
activity-dependent
B antagonists (e.g. Propanolol) pharmacologial effects (6)
- Decreased CO (and HR)
- Decreased Renin release (imp. for HTN relief)
- Increase VLDL, Decrease HDL
- Inhibit lipolysis
- Inhibit compensatory glycogenolysis during Hypoglycemia
- Increase bronchial resistance
Positive effects of nonselectve B blockers on Heart Failure is largely due to _____
decreases in the RAAS
Ultimately lowers vasoconstruction (AT2) and fluid volume (aldosterone)
8 Therapeutic uses for nonselective B blockers (propanolol)
- HTN
- angina
- arrythmia
- CHF (types 1 and 2)
- glaucoma
- migraine
- stage fright
- thyrotoxicosis
Non-selective B adrenergic receptor antagonists that are NOT propanolol
Nadolol
Timolol
Pindolol
Nadolol is less ____
lipophilic than propanolol
Nadolol PK
Long T1/2 (20h)
Mostly excreted unchanged in urine
Nadolol use
HTN
Migraine
Angina
Timolol structure
thiadiazole nucleus with morpholine ring
Timolol uses
HTN
Angina
Migraine
GLAUCOMA
How will B blockers affect pupil size
they wont!
Doesn’t have same effect as cholinergic
Pindolol possesses ________
It is a _________
intrinsic sympathomimetic activity (ISA)
partial agonist
Pindolol less likely to…
cause bradycardia and lipid abnormalities
Pindolol use
HTN, angina, migraine
(PIndolol) Dose response curves and partial agonists
****REVIEW SLIDE****
Drugs that possess intrinsic sympathomimetic activity
ISA
Nonselective B partial agonists
Pindolol and Carteolol
Carteolol less likely to cause ______
bradycardia and lipid abnormalities
Carteolol use
HTN and glaucoma
Nonseletive B antagonists that are used in glaucoma
Timolol, Carteolol
Selective B1 antagonists are considered ______
Examples?
Cardioselective
- Metoprolol
- Bisoprolol
- Atenolol
- Esmolol
- Nebivolol
3rd gen B1 selective antagonists
Nebivolol
Very short acting B1 selective antagonist
Esmolol
(half life 9 minutes)
Moderate lipophilicity B1 selective antagonists
Metoprolol and bisoprolol
Which B1 selective antagonist has significant first pass metabolism
Metoprolol, bisoprolol
Esmolol metabolism
undergoes rapid metabolism by esterases in RBC’s
Metoprolol and bisoprolol use
HTN
angina
CHF
antiarrhythmic
Atenolol use
HTN, angina
Esmolol use
SVT
Afib/Aflutter
Peri-op HTN
Nebivolol causes…
Use?
vasodilaion due to nitric oxide production
**used for HTn
Mechanisms underlying vasodilating actions of B blockers
Ca++ –X-> L-type VGCC –> Intracell. Ca++ –> Contraction
Vasodilation occurs via two pathways
- B2 Agonist – functions via cAMP
- NO – functions via cGMP
Mixed adrenergic receptor antagonists
Labetalol
Carvedilol
Labetalol is a _____ mixture
racemic
Labetalol structure
Two asymmetric carbons
(1 and 1’)
Isomers of labetalol
1S, 1’R = a1 block
both 1 + 1’ R = B block
where does the ‘mixed’ effect come into play with labetalol
The blockade of B (nonselective) stops the reflex tachycardia you’d normally expect with an a1 blocker
Labetalol use
HTN, hypertensive crisis
Carvedilol isomers effects
Both enatomers block a1
Only S-enantiomer blocks B
Mixed effect for carvedilol
Nonselective bet blocking prevents reflex tachycardia from a1 block
Carvedilol use
HTN, CHF 1 and 2
5 AE’s of beta blockers
- Bradycardia
- AV block
- sedation
- mask hypoglycemia Sx
- WIthdrawal
Chronic B blockade results in …
pronounced withdrawal due to upregulation of the B receptors
CI’s for beta blockers
Asthma, COPD, CHF type 4 (final stage)
Catecholamine depleter
reserpine
Reserpine MOA
block vesicular monoamine transporters (NET, DAT)
Depletes vesicular pool of NE!
Reserpine PK
slow onset, sustained effect (weeks)
Reserpine use
HTN treatment (refractory)
Due to it’s slow onset of action, reserpine will _______
NOT activate the baroreceptor response