Problem 3 Apomorphine exhibits a full agonist profile at dopamine receptors. The

Question

Problem 3 Apomorphine exhibits a full agonist profile at dopamine receptors. The experimental drug, EXP, was found to produce the dose response curve shown below. 100 activity EXP -100 logldrug) (M) a) Describe the probable efficacy of EXP at dopamine receptors. b) Using an Allosteric (two-state) model, explain how EXP interacts with dopamine receptors Problem 4 The NMDA receptor is a specific type of ionotropic glutamate receptor. NMDA (N-methyl-D- aspartate) is the name of a selective agonist that binds to NMDA receptors but not to other glutamate receptors. Dizocilpine (Dz) has the following effect on the dose-response of NMDA. The concenration of NMDA alone 100 75 %) 50 25 NMDA with [Dz), response NMDA wth [Dz2 10 9 87 65 logINMDA] (M) a) Describe the probable efficacy of Dizocilpine. b) Draw the probable dose response curve for Dizocilpine without NMDA present.

Explanation / Answer

As apomorphine shows the full agonist profile when binds to dopamine receptor but on the other hand as we can see in the given graph the %activity of experimental drug is given below the basal line which shows that experimental drug is acting as inverse agonist.

Inverse agonist are those drug which binds to the same receptor but they inhibit the pharmacological response opposite to that of agonist. An inverse agonist decreases the activity below the basal line, its efficacy is <0% i.e, it has negative efficacy.

As Exp is inverse agonist drug it binds to the dopamine receptor sites where agonist drug apomorphine has to bind. Dopamine is G-protein coupled receptor. So the action of inverse aganist is studied on both G protein coupled and uncoupled receptor. Both the drugs aganist and inverse agonist given and then studied the ligand binding studies versus agonist. Inverse agonist binding is different for G - protein coupled and uncoupled receptor.

Inverse aganist efficacy is determined from their ability to reduce the sites for full agonist.

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