View Full Version : Please Explain these graphs!

02-10-2010, 11:17 AM
I'm a little confused by the meaning of these graphs, so if anyone would be so kind to explain them I would very much appreciate it! Perhaps they are explaining the different potencies, affinities, or intrinsic activities of drugs???

02-10-2010, 01:05 PM
So the y-axis is the percent of maximum effect (efficacy) and the x-axis is the agonist dose (log scale). We're looking at the change in efficacy and/or potency with all three graphs and figuring out which drug is a noncompetitive antagonist (NCA) or competitive antagonist (CA)

An antagonist either decreases efficacy or potenty, but I'm not sure if an antagonist can do both (please give an example if anyone knows). A competitive antagonist can be overcome by increasing the agonist concentration more than the CA. However, noncompetitive antagonist biochemically change the conformation of the substrate and subsequently, an increase in the agonist has no effect in "pushing out" the NCA because the substrate has been modified by the NCA

NCA shifts the curve downward and a CA shifts it to the right. according to the first graph, M moves down and N moves to the right.

With the second graph, that would be an example of a competitive agonist.

The third graph would be an example of a NCA with varying levels of efficacy. Hope this helps and please confirm and/or leave comments, criticism. thanks.

02-10-2010, 01:07 PM
Also... a shift to the right with CA is a decrease in potency... a shift downward with a NCA is a decrease in efficacy... that can be interpreted from just understanding the axis.

02-10-2010, 05:52 PM
Thank you for taking the time to answer my question! Makes perfect sense now.

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