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Discussion Starter · #1 ·
A laboratory is investigating the interactions of a compound, meropeate, with structurally similar compounds alcyoneate and steropeate. Although they have complimentary effects on their main receptor target, the compounds have different effects on another receptor, Receptor S. Meropeate is an agonist of Receptor S - this is the source of meropeate's main side effect - but steropeate is a competitive antagonist and alcyonate a noncompetitive antagonist. If curve X in the figure represents meropeate alone, what do curves Y and Z represent?

dose-response.gif
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  • Y is meropeate + alcyonate; Z is meropeate + steropeate
  • Y is meropeate + steropeate; Z is meropeate + alcyonate
  • Y is meropeate + steropeate; Z is steropeate + alcyonate
  • Y is alcyonate alone; Z is steropeate alone
  • Y is steropeate alone; Z is alcyonate alone
 

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D) Y is alcyonate alone; Z is steropeate alone

Man!! things are getting really challenging. :redcheeks;

My ans is D) Y is alcyonate alone; Z is steropeate alone

steropeate is a competitive antagonist - curve Z (acting on the same receptor as meropeate agonist acts on)

alcyonate is a noncompetitive antagonist - curve Y (acting on the different receptor)
 

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Discussion Starter · #5 ·
It is true that these compounds do not exist - I think we may see questions on the boards in which we have never heard of the disease or the drug but for which the answer can be reasoned out from basic principles...

The answer isn't D, though - I think if you look back carefully at the question and figure you'll see why!
:)
 

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It is true that these compounds do not exist - I think we may see questions on the boards in which we have never heard of the disease or the drug but for which the answer can be reasoned out from basic principles...

The answer isn't D, though - I think if you look back carefully at the question and figure you'll see why!
:)
I should read all the options carefully, i just saw the first two options and kept on trying to figure out in between them - very silly of me to do it but i keep on doing it because of my impatience. :(
 

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A. Y is meropeate + alcyonate; Z is meropeate + steropeate

I think the answer is
A. Y is meropeate + alcyonate; Z is meropeate + steropeate

Since alcyonate is a non-competitive antagonist, the full agonist will produce a lower response, regardless of the dose.
Graph Z shows that the response is the same but the dose needed has increased, which happens in the presence of a competitive antagonist. So in the presence of steropeate, a larger dose of meropeate is required to produce the same response.

I am not good at explaining stuff but hey I tried.:))
 

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It is true that these compounds do not exist - I think we may see questions on the boards in which we have never heard of the disease or the drug but for which the answer can be reasoned out from basic principles...

The answer isn't D, though - I think if you look back carefully at the question and figure you'll see why!
:)
Okay, so the only other option that has alcyonate is A) so i'll go with A haha :eek:

A. Y is meropeate + alcyonate
 

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Discussion Starter · #11 ·
A is correct!

donofitaly said:
A.Y is meropeate + alcyonate; Z is meropeate + steropeate
doctorsmonsters said:
I think the answer is
A. Y is meropeate + alcyonate; Z is meropeate + steropeate
Since alcyonate is a non-competitive antagonist, the full agonist will produce a lower response, regardless of the dose.
Graph Z shows that the response is the same but the dose needed has increased, which happens in the presence of a competitive antagonist. So in the presence of steropeate, a larger dose of meropeate is required to produce the same response.
Taiyakikung said:
I would go with A.
patelMD said:
A. Y is meropeate + alcyonate
The answer is A. Y is meropeate + alcyonate; Z is meropeate + steropeate. As doctorsmonsters explained,*the addition of a competitive inhibitor like steropeate would shift the dose-response curve to the right (Z). *The maximum fractional response would still be reached, but the antagonist would need to be out-competed by sufficient dose of the agonist. *The addition of a noncompetitive antagonist like alcyonate would suppress the maximal response to the agonist (as in curve Y), and this suppression would not be overcome by a greater dose of the agonist. Either antagonist alone would produce a flat line at zero or even a sigma curve below the horizontal zero(unless one were a mixed agonist, I suppose).
:)

I wrote this question because I fell into the same trap as aktorque and patelMD when I was doing this chapter in pharmacology. I knew the curves of competitive and noncompetitive inhibitors from biochem, and the principle of the sigma-curve here is just the same - except that the "substrate" in this case is the original drug, meropeate. I was confused about this until I realized that the y-axis in these charts was, like v/vmax, a fractional effect rather than absolute effect. Any intrinsic action of the receptor was folded into the idea of fractional effect on the y-axis; so not doing anything would produce a perfect flat line, the addition of an agonist would produce the familiar sigma-curve, etc. I hope that didn't make things more confusing...:eek:
 

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A

A competitive antagonist does not change the Vmax, or in this case the maximum efficacy. It only increases the concentration of a drug needed to reach its maximum response. On the other hand a noncompetitive antagonist will decrease the maximum effect such as in curve X
 

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A competitive antagonist does not change the Vmax, or in this case the maximum efficacy. It only increases the concentration of a drug needed to reach its maximum response. On the other hand a noncompetitive antagonist will decrease the maximum effect such as in curve X
Wow, didn't realize there was already so much discussion on this question!

So if some of you are still not clear, perhaps think of it this way: Curve Y is the baseline curve since the original drug is an agonist. In order to test the efficacy of an antagonist, you need to have an agonist present as well (as far as I know). So the other two curves show how the antagonists affect the activity of the agonist.

These curves are testing percent response. So for an agonist, you can just administer the drug and test its activity. But for an antagonist, it is not as simple. Generally, you need to have some baseline curve for comparison, which in this case is curve Y (agonist only). The other two curves are agonist + antagonist.

Hope that helps. Good question, even better discussion!
 

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Discussion Starter · #17 ·
Wow, didn't realize there was already so much discussion on this question!

So if some of you are still not clear, perhaps think of it this way: Curve Y is the baseline curve since the original drug is an agonist. In order to test the efficacy of an antagonist, you need to have an agonist present as well (as far as I know). So the other two curves show how the antagonists affect the activity of the agonist.

These curves are testing percent response. So for an agonist, you can just administer the drug and test its activity. But for an antagonist, it is not as simple. Generally, you need to have some baseline curve for comparison, which in this case is curve Y (agonist only). The other two curves are agonist + antagonist.

Hope that helps. Good question, even better discussion!
Or, in this question, curve X is the baseline agonist curve, curve Y is agonist + irreversible antagonist, and curve Z is agonist + competitive antagonist... but same idea anyway.
 

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ANS= A

Explaination: In this graph, X is the agonist alone. Y is the agonist + noncompetitive antagonist and Z is the agonist + competitive antagonist. The way to see which one is compt or non compt is by looking at the graph itself. The graph which decreases in height suggests the efficacy is decreased (i.e. non-compt antagnosit). The graph which moves to the right suggests the potency has decreased (i.e. compt antagonist).

The reason why it's A and not D is because we're comparing what happens when we add the antagonists to the agonists in either the competitive or non-competitive forms.

Hope this makes sense.
 
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