Properties of drugs and the concept of receptors Flashcards
what is a drug? (2)
substance of abuse?
medicine example?
endogenous substance examples (2)
Any chemical that has a biological effect
Something ‘given’
Substance of abuse (e.g. cocaine)
Medicine – intention to treat (e.g. aspirin)
Endogenous substance (e.g. insulin, adrenaline)
Properties of Drugs – e.g. Adrenaline
effect on heart? (2)
effect on blood vessels (2)
effect on lungs
effect on liver
chemical selectivity
effect of drug potency?
Variety of effects / tissue selectivity
Heart : increase heart rate and contraction strength
Blood vessels : dilates skeletal arteries but constricts mesenteric arteries
Lungs : dilates airways
Liver : increases breakdown of glycogen
Chemical Selectivity The enantiomer (+)-adrenaline has about 100-fold greater biological effect than (-)-adrenaline
Drugs are very potent
Acts in low concentrations
e.g. 10-9M - 10-15M ranges can produce significant increases in heart rate
Explanation : RECEPTORS
What is a receptor?
B adrenoceptor example
hormone that acts here?
drug that acts here?
Target molecule which physiological mediators and ‘given’ drugs bind to
e.g. β-adrenoceptor in the heart
Adrenaline - physiological hormone
Atenolol – synthetic drug that acts at β-adrenoceptors
blocking the action of adrenaline
General Properties of Receptors
expressed where? effect of this?
selectivity? effect?
amplification? effect? explains what?
Expressed in different tissues
Explains why a drug can have effects on different tissues
Highly selective targets
only specific drug structures bind to receptors
Amplify signals
small number of drug/receptor interactions initiate significant biological effects -> Explains why drug work at low concentrations
Types of receptors
4 different types? examples?
Receptors - Adrenaline acting at β-adrenoceptors
Enzymes - Aspirin acting at cycloxygenase
Carrier molecules - Fluoxetine acting at Serotonin uptake carrier
Ion channels - Lignocaine acting at Na+ channels
Why large number of receptors?
2 reaosns?
what do receptors do? (2)
Many receptors are associated with the cell membrane and are accessible from the outside of the cell (some drugs act inside the cell, e.g. steroids)
Receptors recognises and responses to information – central to body function
receptor (2)
A specific target molecule with which a drug interacts to produce a cellular response
It is not simply a binding site, it alters cell function
Agonist (2)
A drug which binds to a receptor to produce a biological cellular response
e.g. adrenaline increases heart rate
Antagonist (2)
A drug which binds to a receptor (same as an agonist)
but does NOT produce a biological effect
Antagonists bind to receptors and prevent agonists producing effects
e.g. Atenolol blocks adrenaline-mediated increases in heart rate
2 step process of drugs
Occupation governed by affinity
Activation governed by efficacy
Both agonists and antagonists bind to receptors
Only agonists produce a cellular response
HENCE only agonists have efficacy
Classification of drugs
2 different classification
use atenolol as example
Drugs are classified according to:
Clinical use
e. g. Atenolol is used to treat angina
- It is an anti-anginal drug
Target receptor
e. g. Atenolol binds to β-adrenoceptor
- it is a B-adrenoceptor antagonist
Classification of Receptors
Agonists : Noradrenaline (NA), Adrenaline (A), Isoprenaline (Iso)
Antagonists : Prazosin, Atenolol
difference in blood vessels and heart?
Receptors are classified according to:
Agonists and Antagonists that act upon them
Example
Agonists : Noradrenaline (NA), Adrenaline (A), Isoprenaline (Iso)
Antagonists : Prazosin, Atenolol
These drugs bind to adrenoceptors, but their differential actions
define whether an a or B adrenoceptor is involved
In blood vessels: NA > A > Iso to increase constriction
blocked by prazosin (not atenolol)
Termed a-adrenoceptors
In the heart: Iso > A > NA to increase heart rate
blocked by atenolol (not prazosin)
Termed B-adrenoceptors
a/B adrenoceptors have similarities but important differences from each other
