On the subject in the title: Amylin receptor signalling and satiety — what changed since Working notes rather than a conclusion.
What changes if the standard account of Amylin receptor signalling and satiety is wrong? I ask because I have been treating it as settled and I noticed this week that I could not say why.
Working through the consequences rather than the evidence, since others here are better placed on the evidence.
In vitro potency and clinical potency are related by a long chain of assumptions. A compound more potent at the receptor is not necessarily more effective at a tolerable dose.
I have deliberately not rounded that, because the rounding is where the argument starts.
Picking up post #2: that is the part I would want checked first.
Distinguishing three things in the Amylin receptor signalling and satiety discussion that keep getting used interchangeably: the observation, the proposed mechanism, and the recommendation that gets attached to both.
On the opening post — agreed on the reasoning, with one qualification.
Long-term receptor changes: very little is known about what happens to receptor expression, signalling, and downstream effects over years of exposure to these compounds. That is exactly the knowledge gap phase 3 trials exist to fill.
Receptor desensitisation and internalisation are real phenomena in vitro and their clinical relevance to these compounds is not established. That distinction gets lost in discussions about tolerance.
I would treat the number as indicative rather than as a measurement.
Reading back through, this was answered upthread and I missed it. My fault.
I think the Amylin receptor signalling and satiety question is answerable and has not been answered, which is a more optimistic position than most of this thread.
Glucagon receptor agonism raises energy expenditure and promotes hepatic fat oxidation. In a triple agonist the incretin limbs offset the glycaemic consequence, which is why the combination is not self-defeating.
Posted with less confidence than the sentence structure implies.
I read post #8 twice before replying, because I had assumed the opposite.
Ghrelin receptor agonism drives growth hormone release in pulses and also increases appetite, which is the effect people most reliably report and least often want.
Receptor distribution explains the side-effect profile better than anything else. GLP-1 receptors in the gastrointestinal tract and the area postrema account for most of what people report.
I am confident about the direction and much less about the magnitude.
The arithmetic on Amylin receptor signalling and satiety is the easy part and it is where the errors are, which is an uncomfortable combination. Show your working and someone will catch it.
Receptor occupancy required for a clinical effect is not the same as full occupancy, and dose-response curves flattening at the top is what you would expect from that.
The strength of my opinion here exceeds the strength of my evidence.
This follows post #11 rather than contradicting it.
The area postrema sits outside the blood-brain barrier and is where a great deal of the nausea signalling in this class originates. That is why the effect is central and not gastric irritation.
This is the answer, and the reason it is the answer is the more useful part.
Glucagon receptor agonism: glucagon receptor agonism increases energy expenditure and promotes hepatic fat oxidation. The mechanism is distinct from GLP-1 and GIP agonism and the clinical consequences are still being characterised.
That is all I can say without guessing.
Signalling through cyclic AMP is the canonical pathway and is not the only one. Beta-arrestin recruitment differs between ligands and its clinical significance here is unestablished.
That distinction has done more work for me than anything else in this category.
Amylin signalling reaches satiety through a distinct receptor complex, which is the mechanistic basis for expecting an amylin analogue and an incretin agonist to add rather than overlap.
The disagreement above is smaller than it looks once the terms are fixed.
The arithmetic in post #19 is right; the assumption feeding it is the part to check.
GLP-1 receptor agonism produces its metabolic effects through more than one route: central satiety signalling, delayed gastric emptying, and glucose-dependent insulin secretion. Attributing everything to one of them is where most simplified accounts go wrong.
GIP receptor signalling: the glucose-dependent insulinotropic peptide receptor (GIP) is involved in glucose-stimulated insulin secretion. GIP agonism is thought to contribute to tirzepatide's effect but the mechanism is not fully settled.
GIP receptor biology is genuinely contested. Both agonism and antagonism have been argued to produce weight reduction, and the fact that the field can hold both positions tells you how open it is.
Happy to be corrected if someone holds better data than mine.
I would put moderate confidence on the mainstream reading of Amylin receptor signalling and satiety and no more. That is not scepticism for its own sake; it is where the sourcing actually stops.
Post #22 put the caveat in the right place and I want to underline it.
GLP-1 receptor signalling: the GLP-1 receptor is expressed on beta cells (insulin secretion), on neurons (appetite and gastric motility), and on myocardium (contractility). Different tissues respond to the same signal in different ways.
It cost nothing to check and would have cost something not to.
Pharmacological class effects: all GLP-1 agonists slow gastric emptying and suppress appetite. Those are class effects, not unique to one compound. Effects that differ between compounds are usually about potency or receptor selectivity.
Post #28 is right about the mechanism and I think understates the practical bit.
Nothing in receptor biology tells you what is in the vial, which is worth remembering when a mechanistic thread starts being used to justify a sourcing decision.
Reading it back, the second half matters more than the first.
Worth separating Amylin receptor signalling and satiety as a question about the compound from Amylin receptor signalling and satiety as a question about the documentation. They get answered by different people and only one of them is answerable here.