GLP-1 receptor distribution: central and peripheral

Posting this under the heading it deserves: GLP-1 receptor distribution: central and peripheral Everything below is what sits behind that.

I have spent a fortnight trying to pin GLP-1 receptor distribution down and I want to set out where I have got to, because I suspect the honest answer is duller than the thread this will produce.

What I have: a consistent observation across a small number of cases, collected the same way each time. What I do not have: any controlled comparison, or any reason to think my cases are representative.

The specific question is whether the pattern survives once the obvious confounder is removed. I cannot remove it with what I have.

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.

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.

Answering the question post #2 raises rather than the one it answers.

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.

I would want the raw data before agreeing with my own summary of it.

Confirming post #4 from a second method, which matters more than confirming it from a second person.

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.

Someone should write this up properly, and it should probably not be me.

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.

Take it as a starting point and not as a specification.

An honest declaration on GLP-1 receptor distribution: I have a prior here and it is strong enough that you should weight what I say downward. Stating it rather than hiding it.

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.

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.

Speaking for myself and not for anyone else who has posted here.

Noted, and thank you for writing it out rather than summarising it.

Fair, and the limits you put on it are the part I will remember.

On post #9 — agreed on the reasoning, with one qualification.

A note on how GLP-1 receptor distribution gets discussed rather than on GLP-1 receptor distribution itself: the confident posts get the replies and the careful ones get ignored, and the careful ones have been right more often.

Picking up post #13: that is the part I would want checked first.

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.

I am reporting what happened, not recommending it.