Pharmacodynamics Flashcards
What psychological responses are produced through drug-receptor interactions?
When a drug binds to its receptor & changes shape of receptor it can…
- change the CONTRACTILITY of a tissue e.g. muscle
- change the EXCITABILITY of neurones & neural stimulation e.g. morphine & diazepam work by increasing threshold of depolarisation for A.P
- changes in GENE TRANSCRIPTION e.g. insulin causes expression of gene needed for a protein which transports glucose across the cell membrane
Extent of change depends on drugs AFFINITY & EFFICACY
Define partial agonist
Binds to & activates specific receptor. But only has partial intrinsic efficacy = means you get some of the effect but not all the effect
Define antagonist
Chemical which interferes or inhibits the effect of another drug. Binds to receptor & inhibits it. Binds using covalent bonds
Define competitive antagonist
Chemical which binds to receptor at the same active site as the agonist & competes for same binding site. Has NO intrinsic efficacy e.g. narcan
Define a non-competitive antagonist
Binds to a allosteric (non-agonist) site on the receptor to prevent activation of the receptor
Define adrenergic agonist
Drug that stimulates the response from the adrenergic receptors e.g. adrenaline & salbutamol
Define adrenergic antagonist
Drug the inhibits the response from the adrenergic receptors e.g. propranolol (beta-blockers)
Define a chemical antagonist
Binds to the active drug & inactivates it
What is a physiological antagonist
2 agents with opposing effects, they cancel one another out e.g. prostacyclin on platelet aggregation
Which antagonist binds irreversibly to the receptor?
Non-competitive antagonist- bind covalently e.g. aspirin
Albuterol and salbutamol are both beta 2 agonists. Why is salbutamol safer?
Because albuterol also has beta 1 properties = causing tachycardia & tachyarrhymias
Why can’t propranolol be given to asmatics?
Propranolol is a beta 2 antagonist. Therefore would block salbutamol
What is an inverse agonist?
An agent that binds to the same receptor as an agonist but causes a psychological response opposite to that of agonist
E.g. BZs -once bound the receptor cannot shift to active conformation
What is an allosteric interaction?
A secondary binding site on receptors usually enzymes. It can change the affinity of the primary binding site by changing its conformation. Can activate or inhibit
E.g. alcohol increases effect of BZs (allosteric interaction)
Define affinity
How well a drug can bind it it’s receptor. Depends on shape
Define efficacy
Maximum response achievable from a drug - (how effect the drug is).
Define specificity
Degree to which the drug is specific to its aim e.g. reduces side effects
Define potency
The amount of drug required to create an effect - how strong the drug is
How many drugs in the BNF work on 7 transmembrane / g-protein coupled
70%
How does a G-protein transduce the signal across the cell membrane?
- Ligand e.g. NA, morphine attaches to receptor
- Receptor changes shape to accommodate molecule = receptor activates.
- G protein made of 3 sub units. Activated receptor touches G protein = changes shape of G protein
- Alpha subunit drops of & either….
-bumps into cell enzyme = activated enzyme (secondary messenger cascade)
OR
-bumps into ion channel & opens ion channel e.g. morphine activates potassium channel
Give 3 examples that work on second-messenger coupled receptors in the ANS
Atropine, adrenaline + ACh
What receptors does atropine bind to?
Muscarinic ACh receptors but doesn’t activate = mAChR antagonist
The first synapse is always what?…. in both sympathetic & parasympathetic muscle tissue?
Nicotinic
What is the ganglion?
Collection of cell bodies outside CNS
What does inotropic mean?
Relates to the contractility of a muscle.
E.g. adrenaline is a + inotrope (increases contractivity of heart)
What dose chronotrope mean?
Changes speed of HR
E.g. adrenaline is a + chronotrope (speeds up HR)
What would the signs + symptoms be if a pt has a transected spinal cord at C6?
PNS doesn’t go down spinal cord so wouldn’t be affected. SNS would be…. this means the PNS would be unapposed causing…
- bradycardia
- Bronchoconstriction
- SOB
- blood vessels are controlled by SNS… therefore below the transection, the blood vessels would dilate, causing area above to look pale as the blood vessels are constricted above.
What are the effects of atropine on the heart & GI tract?
Heart - removes vagal inhibition
GI tract - removed parasympathetic stimulation = motility & secretions reduced
Adrenergic transmission is activated by what?
Catecholamines (sympathomimetics - mimic the SNS)
Why do you give adrenaline in cardiac arrests?
Not because it’s a cardiac stimulant but to causes constriction of peripheral blood vessels = goes into CNS
Alpha 1 receptors
How does the drug Britaline (ADHD medication) work?
Works on alpha 2 receptors (theses are involved in concentration & inabition of behaviour) by simulating beta 2 = stimulate concentration
What happens if NA/A acted on beta 1 receptors?
Beta 1 mainly on heart muscle cells = increase rate & force of contraction. Same effect on skeletal muscle
What happens if NA/A acted on beta 2 receptors?
Beta 2 receptors mainly on smooth muscle (including respiratory) = relaxation & glycogenolysis (production of glucose)
Adrenaline is a non-specific agonist on all receptor sub-types. What is its effect on alpha 1, beta 1 & beta 2 receptors?
Alpha 1 - vascoconstriction - increased total peripheral resistance
Beta 1 - increased rate & force of heart contraction
Beta 2 - bronchodilator & increased blood sugar
What can you use to treat a beta blocker overdose?
Glucagon
Activation of H1 receptors in response to an infection… what are benefits?
Histamine dilates the capillaries around the injury/sting/bite so that WBCs can get to it (counteract infection)
Why is H1 receptor activation in allergic reactions bad?
You get an over the top reaction
- blood vessels dilate in tissues
- capillaries become highly permeable (leaky) = lose fluid into the tissues = oedema, hives & itching
Antihistamine blocks H1 receptors
What does H2 receptor activation do?
Promotes secretion of HCL in stomach
What does vasopressin do?
It’s an ADH
If the blood becomes dehydrated, ADH is secreted to stop u seeing out. Also control BP (vascoconstrictor)
Works on V1 receptors (smooth muscle) & V2 receptors (distal tubule of kidney)
What are the 4 main types of receptors?
- Agonist (ligand)-gated ion channels
- made up of protein sub-units that form a central pole (e.g.
nicotinic, GABA receptors)
- made up of protein sub-units that form a central pole (e.g.
- G-protein coupled receptors
- Nuclear receptors
- for steroid & thyroid hormones. They are present in cell nucleus &
regulate transcription & protein synthesis
- for steroid & thyroid hormones. They are present in cell nucleus &
- Kinase-linked receptors
- receptors for insulin, cytokines & growth factors