Amylin receptor signalling and satiety — what changed since

Worth separating two things that post #11 runs together.

Bias and desensitisation: receptors can be biased (preferentially activating some downstream pathways over others) and can desensitise over time (responding less to the same stimulus with repeated exposure). Both might affect long-term response to these compounds.

Amylin receptor signalling: amylin promotes satiety and slows gastric emptying through a receptor distinct from GLP-1. The hypothesis behind combination therapy is two complementary satiety mechanisms.

Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.

Central versus peripheral action: GLP-1 agonism works through both central nervous system effects (appetite) and peripheral effects (gastric motility, insulin). The balance is not fully characterised.

On post #15 — agreed on the reasoning, with one qualification.

Two things before anyone answers the substance.

First, the context in the first post is clear and specific. Second, the question is framed so that an answer can actually address it. Both are the norm here and both matter more than they sound.

post #19 answers the question as asked. The question underneath it is different.

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.

I disagree with the reply above, and I think the disagreement is substantive rather than terminological.

The distinction being drawn does not survive when you look at the published data for this specific question. I would be glad to be shown wrong on this, because the version I am arguing against is more convenient.

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.

This follows post #20 rather than contradicting it.

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.

Cross-reactivity and selectivity: the compounds are not perfectly selective for their target receptors. Semaglutide has some activity on other receptors; tirzepatide activates both GLP-1 and GIP with different affinities. The off-target effects are part of the overall pharmacology.

Species differences: rodent studies show the same compounds produce effects in rodents that predict human effects reasonably well for semaglutide and tirzepatide. The track record is less clear for novel compounds with less human data.

On post #22 — agreed on the reasoning, with one qualification.

Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.

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.

Species differences: rodent studies show the same compounds produce effects in rodents that predict human effects reasonably well for semaglutide and tirzepatide. The track record is less clear for novel compounds with less human data.

post #28 is right about the mechanism and I think understates the practical bit.

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.

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.