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Data Interpretation Practice Question: Lowacidine Schild Plot Histamine stimulates the release of hydrochloric acid from parietal cells in the stomach muscosa by binding to histamine
Data Interpretation Practice Question: Lowacidine Schild Plot
Histamine stimulates the release of hydrochloric acid from parietal cells in the stomach muscosa by binding to histamine H receptors. The potency of a novel reversible H receptor antagonist, Lowacidine was investigated using isolated gastric mucosa from the rat.
Dose response curves were prepared in the absence and presence of Lowacidine In cases where Lowacidine was used, it was applied h before the histamine. The effects of Lowacidine were determined at four concentrations, and the resulting EC values are shown in the table below:
Lowacidine concentration M Histamine ECM
x
x x
x x
x x
x x
a Explain what is meant by the term EC In outline, how do you suggest the EC for histamine would have been determined in this example?
b Explain the meaning of the term pA value for a competitive antagonist.
c Determine the pA value for Lowacidine by plotting a Schild Plot of the effect of Lowacidine on histamine induced acid secretion
The pA values for a further drugs under test AE on histamine induced acid secretion were determined and are shown on the table below.
Drug pA
A
B
C
D
E
d Which drug in the table is the most potent antagonist? Justify your answer. What concentration of drug C would produce an EC of x M Explain your answer fully.
PTO
In further studies the effect of Lowacidine as an antagonist at other histamine receptor subtypes was explored by using histamineinduced contraction in guineapig ileum H receptor and histamineinduced H receptor presynaptic inhibition of acetylcholine outflow in an isolated myenteric plexus preparation. The table of pA values generated is shown below.
Preparation receptor
Ileum
H Gastric mucosa H Myenteric Plexus H
pA value
Your data from above
e Suggest why the pA values for Lowacidine are different at each histamine receptor subtype. Explain why the testing of the Lowacidine at a number of differing histamine receptor subtypes is necessary.
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