Lectures 12, 13, 14, and 15 Flashcards
What are the functions of beta 1 receptors?
Stimulate renin release in kidney and increase heart rate and contractile force of heart
What are the functions of beta 2 receptors?
Stimulate vasodilation of skeletal muscle and bronchodilation of lungs
What conformation do noradrenaline and adrenaline bind to an adrenergic receptor?
Trans conformation (w/ respect to nitrogen and beta OH)
Which absolute configuration is preferred in the adrenergic receptor?
R absolute configuration
What must be done to make a beta antagonist?
- Retain high affinity for beta receptor
- Eliminate intrinsic activity
- Have higher affinity for beta vs. alpha receptors
What effect do isopropyl and t-butyl have on alpha and on beta receptors?
- Alpha receptors – decrease potency
- Beta receptors – increase potency
What does an isopropyl N-substitution do?
Confers beta selectivity
What does addition of a sulfonamide to the meta position do?
Makes the molecule resistant to COMT, but still only a partial agonist
What does a para sulfonamide plus an isopropyl group do?
Makes the compound a weak antagonist
Is pronethalol or propranolol used more often and why?
Propranolol b/c pronethalol is toxic and possibly carcinogenic
What is the difference btwn arylethanolamine and aryloxypropanolamine?
Position of attachment of ethanolamine or oxypropanolamine w/ respect to ring substituents
Are arylethanolamines or aryloxypropanolamines more potent?
Aryloxypropanolamine
What are aryloxypropanolamines used for?
Binding to beta receptors
Does a t-butyl group produce beta 2 antagonist selectivity?
No, only beta 2 agonist selectivity
What effect do para substitutions of aryloxypropanolamines have?
- Confer beta 1 vs beta 2 selectivity, so can produce cardioselective beta 1 antagonists
- Must be single para substitutions
For arylethanolamine, the active isomer is ___
R and D
For aryloxypropanolamine, the active isomer is ___
S and D
How can effects of competitive antagonists of beta 1 (and sometimes beta 2) receptors be overcome?
Increased noradrenaline or adrenaline
What are some effects of beta antagonists?
- Decrease heart rate, stroke volume, and force of contraction => decrease blood pressure
- Decrease renin release in kidney (may be secondary mechanism to decrease BP)
- Decrease intraocular pressure by decreased production of aqueous humor (used to treat glaucoma)
What effect do non-selective beta antagonists have on the lungs?
Can cause bronchoconstriction and precipitate an asthmatic attack in those w/ asthma
What makes the beta antagonists classified as class 2 antiarrythmic agents?
MSA (membrane stabilizing activity) or local anesthetic effect
In which beta antagonists is MSA higher?
Those w/ high LogP
When are MSA effects seen w/ beta antagonists?
At doses higher than what is needed for beta antagonist activity
What is the MSA of propranolol?
Potent MSA b/c can penetrate BBB and cause CNS effects
Nadolol is like the ___ version of propranolol
Hydrophilic
What is timolol mostly used for?
Glaucoma tx as eye drops
What is bunolol mostly used for and what is significant about it?
- Glaucoma tx as eye drops
- One of the few beta antagonists that come as S isomer only
Which beta antagonists are arylethanolamines?
Sotalol and labetalol
What is pindolol used for? Does it have MSA?
- Hypertension tx and as an adjuvant for depression tx
- Has MSA
What is a common characteristic of the structure of selective beta 1 antagonists?
Single para substituent that is typically an aliphatic straight chain and hydrophobic
Which beta 1 antagonists have MSA?
- Metoprolol
- Acebutolol (some MSA)
- Betaxolol (some MSA)
- Bisoprolol
What effect does an sp2 hybridized NH in the meta position have?
Provides partial agonist activity but keeps competitive antagonist activity
What is labetalol used for?
Tx of high BP and heart rate
Is labetalol used often? Why or why not?
No b/c is a beta 1, beta 2, and alpha 1 antagonist
What is the main use of carvedilol?
Seen to decrease morbidity and mortality in heart failure and in post-acute MI patients
What are uses of beta blockers?
- High blood pressure (not first line, and use is decreasing)
- Arrhythmias (generally safe but not effective for prevention)
- Heart failure
- Angina*
- MI/heart attack (life saving drug both during MI and for tx after)
- Glaucoma*
- Migraines (rare)
- Tremors (rare b/c condition is rare)
What are some side effects of beta blockers?
- Fatigue
- Bronchospasm (only w/ asthmatics on non-selective beta blockers)
- Cold extremities
- Left ventricular insufficiency
- GI (nausea, vomiting, diarrhea, abdominal pain)
- CNS effects (hydrophobic beta blockers)
What are contraindications of beta blockers?
- Asthma (beta 1 selective are fine)
- Bradycardia
- Diabetics (sometimes)
What effect does LogP have on a beta antagonist?
Increased LogP = increased hepatic metabolism, decreased t1/2, decreased urinary excretion of unchanged drug, and decreased bioavailability
What type of metabolism can aryloxypropanolamines undergo?
- N-dealkylation (removal of isopropyl or t-butyl) => inactive metabolite, which can be oxidized by MAO
- Aromatic hydroxylation => active metabolite
What is significant about esmolol?
Beta 1 antagonist that is metabolized by esterases, which decreases t 1/2 and allows HCP’s to have tight control over effect (rapid onset and quick elimination)
What is esmolol used for?
As continuous infusion for atrial fibrillation
Describe acebutolol metabolism?
Acebutolol (active) – amidase –> inactive – NAT –> diacetolol (active)
Acebutolol and diacetolol are ___ selective antagonists
Beta 1
What is different btwn diacetolol and acebutolol?
Diacetolol has longer t 1/2 and is found in higher concentration in plasma and has partial agonist activity
What should be given to a px that is having an MI or had an MI?
Beta blocker!!
Where and when is renin released?
Kidneys when BP sensing cells detect a decrease in BP
What is the function of angiotensin converting enzyme? How does it do this?
- Converts angiotensin 1 into angiotensin 2 and makes bradykinin inactive
- Cleaves histidine and leucine on C terminus to make angiotensin 2
What is the function of renin as an enzyme? How does it do this?
- Converts angiotensinogen into angiotensin 1
- Cleaves valine and other aa’s on the C terminus to make angiotensin 1
What are the effects of angiotensin 2?
- Vasoconstriction => increased BP
- Increase ADH => vasoconstriction => increased BP
- Increase ADH => increased H2O => increase blood volume, stroke volume, CO => increased BP
- Increase aldosterone => increased Na+ and H2O and decreased K+ => increased BP
What are the effects of bradykinin?
- Can increase prostaglandin synthesis => vasodilation
- Vasodilation => decreased SVR => decreased BP
What is another name for ACE and where is it primarily found?
- Kininase 2
- Mostly found in lungs
What receptors does angiotensin 2 bind to and what does this cause?
- Angiotensin 1 receptors (AT1)
- Causes vasoconstriction, increased release of aldosterone from adrenal cortex, and increased ADH
Angiotensin 1 receptors is G alpha __
q
What effects does the angiotensin 1 receptor have around the body?
- Arterioles – vasoconstriction and increased BP
- CNS – increase ADH
- Adrenal cortex – increase aldosterone
- Kidney - decrease renin through negative feedback
- Cellular effects – increase phospholipase C, IP3, DAG, and intracellular calcium, and decrease K+ outflow
What are the ligands of angiotensin 1 receptor?
A2 and A3
What is the function of AT receptor blockers?
Prevent A2 from binding to AT 1 receptor
What are renin inhibitors used for?
Treating hypertension
What is the only approved renin inhibitor and what does it do?
- Aliskiren
- Mimics angiotensinogen, so blocks conversion of angiotensinogen into A1 => lower levels of A2 => decreased vasoconstriction, blood volume, and BP
- Reversible competitive inhibitor
What is significant about teprotide?
- First residue is a pyroglutamate (cyclic glutamate)
- Has many proline residues that decreases proteolytic degradation
- ACE inhibitor
What is a disadvantage to teprotide?
No oral bioavailability
What peptide can become the lead compound for developing a new drug from teprotide?
Ac-FAP (phenylalanine and proline)
What is an advantage and a disadvantage to Ac-FAP?
Binds to active site, but can be hydrolyzed by ACE
What effect does zinc have on Ac-FAP?
Polarizes the C=O bond, making it a better electrophile
What are S1, S1’, and S2’?
Binding pockets of ACE
What are disadvantages to captopril?
- Causes taste disturbances and rashes
- Can oxidize to form disulfide bonds
- Very short t 1/2
- Most problems attributed to high affinity zinc binding group SH (solution = dicarboxylate ACE inhibitors which replace SH w/ COOH)
What is significant about enalapril?
Pro-drug (catalyzed by esterases)
What is significant about lisinopril? (*common exam question)
Only ACE inhibitor that doesn’t need to be a pro-drug b/c di-zwitterion is electrically neutral