| Metabolites | Response generated |
|
| Met 1 | added to receptor  |
--- |
| Met 2 | '' |
--- |
| Met 3 | '' |
--- |
| Met 1 + 2 | '' |
--- |
| Met 2 +3 | '' |
--- |
| Met 1 + 3 | '' |
--- |
| The TRIPSE | |
Answers written by a student to the TRIPSE problem 'Nuts about Grapes' (example 2)
Student name: K.L.
LIST 1 -3 POSSIBLE "EXPLANATIONS" FOR THE OBSERVATIONS MADE.1. The addition of the red wine has an effect on the agonist activity. A component of the red wine causes the agonist to be broken down more readily. Bioavailability of the agonist phenylephrine is less and therefore not as much agonist is available to elicit a response by binding to the receptor. This component can be a metabolite of red wine that is not readily formed in white wine. Other agonists that cause relaxation are now in a higher concentration than PE and bind the receptor (competition agonist).
2. A metabolite that is produced from a breakdown of red wine can also act directly on the receptor. It can change the conformation of the receptor so that it does not bind the agonist as readily. A reduction on response occures. The conformational change may act in an opposing effect (ie contraction) when the agonist binds.
3. An enzyme present in red wine breaks down the agonist into "SUB-agonist components". These metabolites elicit a relaxation response wehn they are exposed to the receptor. Their chemical structure is different from the structure of PE. This structure of the agonist and its interaction with the receptor causes relaxation.
CHOOSE ONE OF THE EXPLANATIONS YOU HAVE
GIVEN.
DESIGN AN EXPERIMENT OR EXPERIMENTS TO EXPLORE THAT EXPLANATION FURTHER.
You will have 20 MINUTES to answer. Please hand your work to the instructor.
Response #3 was chosen to develop an experiment.
An enzyme present in red wine breaks down the adrenergic agonist phenylephrine (PE) into metabolites that have agonist characteristics. One such metabolite that is produced binds to the receptor and causes relaxation.
Investigation
The metabolic pathway of PE must first be investigated. The enzyme present in red wine must be isolated. The effect that this enzyme has on the agonist can be investigated by altering (increasing / decreasing) its concentration in the enzyme agonist mixture. If the addition of the enzyme breaks down the agonist into metabolites the concentration of the metabolites should increase if the enzyme concentration increases.
Once the metabolite structures are determined each metabolite should be isolated. The metabolite of interest is the one that acts on the receptor to cause relaxation. A combination (2 or more) of metabolites can act on the receptor to relax the muscle. In order to isolate the compound that is binding to the adrenergic receptor and relaxing the muscle subsequent trials must be set up.
Suppose there were 3 metabolites produced from the breakdown of PE.
| Metabolites | Response generated |
|
| Met 1 | added to receptor |
--- |
| Met 2 | '' |
--- |
| Met 3 | '' |
--- |
| Met 1 + 2 | '' |
--- |
| Met 2 +3 | '' |
--- |
| Met 1 + 3 | '' |
--- |
The response generated can be measured by the trials listed above. The magnitude of the contraction response can be recorded and compared between trials.
Suppose for instance that metabolite 1 only caused contraction. This would appear to be the agonist that elicits the contraction. This metabolite can be specific for adrenergic receptors. This hypothesis can also be tested by noting the response when it binds to different types of receptors (eg cholinergic receptors).
You have been provided with additional material.
Read it through carefully and reassess your explanations in view of the new information
provided.
Return to the room at the time indicated and hand over your answers to the instructors.
Make sure that your name is on the sheet.
My interpretation of this problem discussed metabolism of the present agonist (PE) and the effects that its metabolites had on the adrenergic receptors. This was the wrong approach. I focused too heavily on the agonist-receptor relationship and did not consider a second messenger pathway. It is true that a component of grape skins is the factor responsible for the initiation of these reactions. My belief was that the component was an enzyme that caused the breakdown of PE (into agonists). These metabolites caused the relaxation process.
This theory did not focus on the second messenger pathways. The fact that the relaxation response was lessened after the tissues were denuded of endothelium was a key factor in the production of a hypothesis. Unfortunately, I ignored this fact and did not consider the possibilities involved. These findings prove that it is some component in the endothelium that causes relaxation and not specifically a receptor-PE metabolite interaction.
Grape skin is the factor that should have been involved in my explanation. Its interaction with the endothelium caused an increase in cGMP levels. This concentration invease leads to a cascade of reactions and an opposing effect of relaxation.
Obviously there are a number of factors that I ignored in my production of a hypothesis. It is difficult to decide on the component responsible for a measured response and then to decide which rate it takes in order to elicit that response. Our focus on metabolites and the breakdown of felodipine and the grapefruit problem influenced my ideas in this problem. I failed to consider a more complex system of second messengers. This is a difficult problem to overcome in science. Deciding what causes a response and what is responsible for a decrease or increase in the response is difficult. The scientists (in this journal) are still not confident on what component of the grape skin causes an increase in cGMP. This is the mystery and frustration of science. Scientists and pharmacologists must continue to investigate and hopefully find the answers to these questions.
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