Physiology and Pharmacology 2: (Evans) Flashcards
Langmuir equation?
Xa / (Xa + Kd)
Multiply by Bmax to fit real biological data (as long as it obeys law of mass action)
What can you estimate with Kd?
Kd is an estimate of affinity
low Kd = high affinity
high Kd = low affinity
What is EC50? What is it a measure of?
Effective concentration of agonist evoking 50% of the maximum response
- Measure of drug potency
Why is EC50 nearly always lower than Kd?
Because of receptor reserve
i.e not all receptors must be occupied to produce a maximum response
Model Equation for ‘response’ with respect to EC50? Explain terms
Xa = conc. of agonist n = slope factor EC50 = conc. of agonist evoking 50% max response max = max response amplitude
max.[Xa]^n / ([Xa]^n + [EC50]^n)
Which is the hill slope indicative of?
The number of molecules that bind to each receptor
hill slope > 1 indicates multiple molecules needed to bind
What is indicated by 2 curves, One with 100% Bmax, one with 70%, but with the same EC50?
One of them is a partial agonist (70%) (can never achieve 100% maximum response
What is efficacy?
The measure of a single agonist-receptor complex’s ability to generate a response, 0 -> 1
1 = full agonist
0 = binding to receptor, no response
What is an antagonist? Classes on antagonism?
A drug that prevents the response of an agonist
- chemical antagonism
- pharmicokinetic antagonism
- physiological antagonism
- non-competitive antagonism
- competitive antagonism by receptor block
What is chemical antagonism? Examples?
Agonist is chemically altered by the antagonism -> substances combine in solution such that the effect of the agonist is lost
e. g. treatment of heavy metal poisoning via chelating agents
e. g. cytokine inactivation by injecting neutralising antibodies
What is pharmacokinetic antagonism? Examples?
Reduction in the amount of drug absorbs
e.g. decrease in absorption via the GI tract
or
Change in the rate of renal excretion of an agonist
e.g. aspirin reduces rate of renal excretion
or
Change in drug metabolism
What is physiological antagonism? Examples?
The interaction of 2 drugs with opposing actions in the body
e.g. noradrenaline raises arterial blood pressure by acting on the heart and peripheral blood vessels, while histamine lowers arterial pressure by causing vasodilation
What is non-competitive antagonism? examples?
Blocks some step in the process between receptor activation and response i.e it does not compete with the agonist for the receptor site
e.g. metabolic inhibitors
What is competitive antagonism? Sub-divisions?
COmpete with the agonist for occupancy of the receptor
(binds to receptor, 0 response)
Reversible or Irreversible
