| Author |
 Topic  |
|
|
tibiriandre
Burkina Faso
Posts |
 Posted - 04/16/2013 : 5:04:44 PM
|
Origin Ver. and Service Release (Select Help-->About Origin):
Operating System:
I need Help!
I have recorded some data from plant extracts, lets say Extract A, Extract B and Extract C. I am studying their relaxation effect on rat aortic rings. From these data, I want to know the EC50 of each extract. For each set of data, I performed statistics on row to compute the mean and SEM. After that, I have plotted the graphs %Relation = f(log[C]). To obtain the EC50, I have used the non-linear curve fitting function; Pharmacology then Dose-Response. So, I have got EC50 values of 7.55, 14.97, 9.25 respectively for extract A, extract B and extract C (please, find attached file). But I am getting trouble with these values: do really extracts B and C can have these EC50 values? With the screen reader, we can see that the maximum of relaxation of these two extracts is about 20% for a concentration of 12 mg/mL. So, I think that something is going wrong. Can anyone explain me?
Many thanks in advance !
http://www.originlab.com/ftp/forum_and_kbase/Images/Vasorelax.opj |
|
|
meili_yang
103 Posts |
Posted - 04/16/2013 : 6:35:00 PM
|
Hi,
By looking at your SE of EC50 for Extract A, B and C, Extract B gives an unreasonable SE which is even higher than EC 50. And the SE of A2 for Extract B is extremely large. It's probably because there is not enough data to perform an s-shape curve all the way down. Fitting is based on only a part of the entire curve. Then it can cause a problem. One way to get a better estimation is to fix A2 for Extract B to a reasonable value, for example 20. It then will give you EC50=7.32 with acceptable SE.
To change parameters, click on lock shape button on the left top. Choose change parameters and the fit dialog will open. Under parameters you can choose A2 for Extract 2 is fixed, and perform the fit once again.
Hope it can help.
Regards,
Meili
OriginLab |
 |
|
|
tibiriandre
Burkina Faso
Posts |
Posted - 04/17/2013 : 06:31:44 AM
|
Hi Meili
Thank you for the help.
Can you help me again: what is the meaning of A2 or A1?
Regards ! |
|
|
|
meili_yang
103 Posts |
Posted - 04/17/2013 : 11:36:44 AM
|
A1 is lowest observed relaxation percent value and A2 is the highest.
Meili
OriginLab |
|
|
|
tibiriandre
Burkina Faso
Posts |
Posted - 04/17/2013 : 12:10:00 PM
|
Thank you very much!
Regards! |
|
|
| |
Topic |
|
|
|
Interpolated EC50 values