Agonists and Antagonists Practical Flashcards
What is an organ bath experiment?
When isolated tissues are suspended in a fluid filled, heated and gassed chamber.
Allows to study nerve conduction (synapsis) and contraction of muscle fibres (Smooth mainly)
What are the advantages of a organ bath experiment?
Living tissue used - show drug-receptor interaction, signal transduction, functional output
Direct cause and effect
Quantification and characterisation of pharmacological action (maximal response, EC50, affinity, mode of action (agonist or antagonist)
Treatments for what conditions have been developed by an organ bath experiment?
Hypertension
Heart failure
Diabetes
Gastrointestinal disease
Bladder dysfunction
Asthma
Thrombosis
What organs are commonly used in an organ bath experiment?
Guinea pig ileum
Rat thoracic aorta
What temperature is the organ bath heated to normally?
37 degrees
What is the difference between dose-response curve and concentration-response curve and when should they be used?
Dose-response - normall for in vivo experminets, know the dose given but not necessarily the concentration at the receptor
Concentratration response - in vitro where direct control over concentration of drug exposed to the tissue.
Drug effects are more dependent on concentration at the receptor not necessarily the dose added to the system.
What is the use of phenylephrine?
Chemistry: alpha-1 adrenergic receptor agonist, structural analogue of noradrenaline
Clinical: Used in the treatment of hypotension will induce local vasoconstriction (also dilates pupils), normally injected to treat hypotension caused by shock or anaesthesia.
Pharmacology: binds to alpha 1 adrenoreceptors - GPCR - conformation change causes exchange of GDP to GTP, activates receptors, activates PLC, increased levels of DAG and IP3 results in activation of PKC and increased Calcium ion concentration results in smooth muscle contraction.
Physiology: calcium ion binds to calmodulin, activates MLKC, phosphorylated myosin light chain results in smooth muscle contraction.
Increase SVR.
What is the use of acetylcholine on smooth muscle in gut?
**Chemistry: targets muscarinic receptors (M3) which is a GPCR
Pharmacology: activates PLC, resulting in splitting of PIP2 into IP3 and DAG, increases Intracellular calcium ion conc causing muscle contraction
Physiology: increases parasympathetic tone via vagus nerve stimulation, amplitude of peristalsis contraction, and secretory active of GIT and relaxes sphincters.
What is the use of sildenafil?
Clinical: indicated for pulmonary arterial hypertension, erectile dysfunction and digital ulcers.
Chemistry: is a phosphodiesterase (PDE5) inhibitor, molecular structures mimics cGMP
Pharmacology: competitive inhibitor of PDE5 binding to catalytic site, prevents PDE5 from breaking down cGMP.
cGMP-dependent protein kinase pathway is activated, phosphorylates multiple targets in smooth muscle cells, decreased intracellular calcium, resulting in deactivation of MLKC resulting in smooth muscle relaxation.
Physiology: Vasodilator/relaxation of smooth muscles (allows corpus cavernosum to fill with blood in erevtile dysfunction)
What is the use of atropine?
Clinical: indicated to treat bradycardia and relieve gastro-intestinal disorders characterised by smooth muscle spasm.
Chemistry: heterocyclic ring.
Pharmacology: non-specific c reversible antagonist of muscarinic (cholinergic) receptors.
Physiology: effects areas acted on by post-ganglionic cholinergic nerves.
What is the use of pilocarpine?
Clinical use: treat dryness of the motuh and throat caused by a decrease in saliva (sjogrens syndrome or after radiation for cancer of head/neck), lower intraocular pressure in glucoma
Chemistry: alkaloid, cholinergic drug
Pharmacology: partial agonist at muscarinic receptors
Mainly M3 (GPCR) activates the PLC secondary messenger pathway to increase calcium ion concentration, resulting in smooth muscle contraction.
Also an agonist at M1 and M2 receptors - may cause bradycardia and hypotension
Physiology: Miosis, increased smooth muscle tone
What is the use of histamine on the ileum?
Pharmacology: H3 receptors on smooth muscle of the ileum, mediates inhibition of muscle contractility.
Physiology: hyperpolsriastion due to increased permeability to K+ channels.
Clinical: vasodilator, inhibit contraction of smooth muscle
What is the use of mepyramine on the ileum?
Clinical: is an anti-histamine
Pharmacology: targets the H1 receptor found on smooth muscle, blood vessels, skin nerves and brain.
Selective receptor reversible competitive antagonist,
competing with histamine for the binding site, does not cause a response itself.
Shows surmountable antagonist as effect is altered by changing the concentration of histamine/mepyramine.
What is the effect of acetylcholine on the cardiovascular system?
Chemistry: Neurotransmitter, released by vagus nerve
Pharmacology: Mucarinic receptors
SA node: binds to M2 receptors (GPCR), open acetyl-choline activated potassium ion channel - hyperpolarisation of SAN - no firing of the action potential as greater than normal stimuli required.
Aorta: M3 receptors (GPCRS) in smooth muscle in tunica media:
Activated alpha subunit, Causes inhibition of adenylate cyclase, reducing conversion
Physiology: negative chronotopic and ionotropic effects, dilated aorta, reduced cardiac output and reduced flow rate. **
What are the different pieces of equipment in the organ abth experiment?
Chart recorder
Force transducer
Tissue
Valve
Coil
Valve
Reservoir
What is the role of the chart recorder in organ bath experiment?
Records measurements from force transducer
What is the force of the force transducer in an organ bath experiment?
Measures the force at which isolated tissue contracts
What is the role of valves in the organ bath experiment?
Two valves
One can be opened to drain the tissue chamber
One can be opened to fill the tissue container with fluid from the reservoir
What is the role of the coil in the organ bath experiment?
Heats physiological solution to 37 degrees before it coats the tissue\
Ensures tissue is kept at body temperature
What is the role of the reservoir in the organ bath experiment?
Contains the physiological solution that is used to suspend the tissue in.
What is important about the timing of the wash cycle in an organ bath experiment?
Ensure tissue is not exposed to drug for too long - or risk damaging the desensitising tissue
Must be immersed in physiological solution or will dry out.
How often should you wash the tissue between adding drugs of different concentration?
Twice
What are the negatives of an organ bath experiment?
Tissue is very fragile - must be treated carefully or will break down
Real tissue can be expensive and difficult to get hold of - ethical debate and requires specialist lab conditions.
What is meant by a partial and full agonist?
Full agonists - bind to tissue receptors and produce a maximal response
Partial agonist - bind to tissue receptors and produce a submaximal response
What is meant by an antagonist?
Bind to sites without causing activation, have no efficacy
What is a competitive antagonist?
Antagonist or agonist can be accomodated by the receptor - can not accommodate both at the same time
Therefore increasing the concentration of one will decrease the effect of the other
Antagonism is said to be surmountable.
A competitive antagonist will shift the curve of an agaonist to the right with no change in maximal effect of shape.
Effect can be reversible or irreversible
How is the effect of a reversible and an irreversible antagonist different?
Reversible - will dissociate from recepto, rate of dissociation affects the ability of antagonist.
Irreversible - does not dissociate or dissociated very slowly from the receptor, effect remains the same, efficacy will not eventually return to maximum.
How can partial agonists be used as antagonists?
Partial agonists may compete with full agonists
Binding of partial agonist has a lower efficicay of a full agonist, therefore reduces response to submaximal (can mimic the effect on an antagonist)
What is meant by physiological antagonisms?
When a drug binds to a receptor different to the agonist it brings about opposite effects of the agonist
What is the difference between affinity and efficacy?
Affinity - strength of drug binding with receptor
Efficacy - ability of a drug-bound receptor to produce a response
sWhat is the difference between specificity and selectivity?
Selectivity - the ability to discriminate between and preferentially bind to one type of receptor.
Specificity - the extent to which a drug produces only the desired therapeutic effect.
What is meant by receptor sub-types?
A distinct variation or classification within a larger group of receptors that share similar functions but may differ in their specific properties, structures or responses to stimuli.
For example beta adrenergic receptors can be further subdivided into beta 1 and beta 2 adrenergic receptors.
What is meant by the maximal response of a drug?
The maximum efficaciy/response on a dose or concentration-response curve
Often when all receptors are saturated as much as they can.
What is EC50 of a drug?
The concentration of a drug where is acts at 50% its maximal efficacy.
What is the Hill coefficient?
Devised based on the binding of oxygen to haemoglobin (hence for enzymes typically with an S shape curve).
Used to measure cooperativity in a binding process, this is when the shape of an enzyme is altered by another molecule or substrate binding, this effects how well the enzyme binds to the substrate
Value of 1 = no cooperativity
Negative value = binding of first one lower affinity for binding of second molecule
Positive value = binding of one increases affinity for binding of another.
What is the equation linking concentration and volume?
C1V1 = C2V2
How do you calculate dilution coefficient?
New volume/old volume
or
new conc/ old conc
How should you read a logarithmic scale?
Find difference between two large values
Divide by number of divisions between values
This is the addition for each small mark
Aka same as normal scale but lines are bunched to one side and calculation must be prepared between each larger division.
What is the key idea of animal testing?
Regulated by the Animals (scientific procedures) Act in 1986
Permits the use of animals as long as there is no alternative, when unavoidable requires a minimal number of animals and taken steps to mimit any pain, suffering or distress
This helps scientisies replace, reduce and refine animal testing.
How are most animals used in biomedical research?
Blood tests
Injections (e.g introduce chemical into blood stream)
Monitor and influence behaviour
May be killed so tissues and organs can be modified
Animals are genetically engineered or bred to be genetically identical.
UK band testing cosmetic production (and ingredients) on animals since 1998.
EU also bans the sale of cosmetic products containing ingredients on animals tested after 2013.
What do you need to be cautious of in phenylephrine use?
Reflex bradycardia
Arryhtmias and palpitation
Contraindicated for hypertension, also thyrotoxicosis in children for eye use.
What is meant by surmountable antagonism?
When a drug is an antagonist sometimes
It has a greater antagonistic effect at higher concentrations relative to the competing agonist concentration
