THE ACTIONS OF DRUGS ON THE GUINEA-PIG ISOLATED ILEUM
1. Supplied with a spreadsheet of all the class results. Fill in the table (see next page) for all 4 types of agonist/antagonist combination used. Using appropriate
statistical tests on the class data, examine whether in each case the presence of the antagonist increased the log EC50 value of the agonist significantly (in other
words, made it less negative)*. You may use a calculator or a computer program to do the statistics. Indicate on the table the results that are significant
* Note: the statistical tests you use should be done on the log EC50 values, rather than EC50 values, because it is only the log EC50 values that have an approximately
Normal (bellshaped) distribution; in contrast, the EC50 values usually have a skewed distribution. Many (though not all) statistical tests are valid only if the data
are approximately Normally
2. This question tests your understanding of the practical and the relationship between agonists and antagonists. From your knowledge of the pharmacology of the
agonists that were used, and the observed changes in the EC50 values from each of the 4 drug combinations:
(i) To which drug classes do antagonists X and Y belong (i.e. which receptor types do you
think they act upon)?
(ii) With reference to the class practical results in the table (page XX), describe in detail
what the experimental evidence is for your answers to question 3(i). This justification
of your conclusions is a very important part of this practical write-up.
(iii) After using a pharmacology text book and your lecture notes, write down a possible
name for drug X and a possible name for drug Y.
3. The experimental protocol for this practical involved determining two log concentration
response curves, the first one in the absence of the unknown antagonist and the second one
in its presence. Could this experimental protocol lead to any error and, if so, and how might it be avoided (e.g. by modifying the protocol)?
Your write-up should consist of the table, and the answers to the above questions. The written answers should be typed, if possible, and should be no more than 2 side
of A4 paper (use 12 point text, double line spacing). Be brief – marks will be deducted for rambling answers that do not stick to the point. Qu 1, 6 marks; Qu 2, 8
marks; Qu 3, 2 marks.
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