This is a continuation of a long topic, addressed by post number rather than by page. Start at post 1.
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.
I read post #60 twice before replying, because I had assumed the opposite.
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.
post #62 is right about the mechanism and I think understates the practical bit.
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.
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.
Picking up post #62: that is the part I would want checked first.
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.
Coming back to post #64, because the follow-up matters more than the original answer.
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.
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.
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.
This follows post #66 rather than contradicting 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.
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.
Worth separating two things that post #67 runs together.
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 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.
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 #71 — 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.
post #75 answers the question as asked. The question underneath it is different.
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.
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.
post #79 is right about the mechanism and I think understates the practical bit.
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.
post #80 is right about the mechanism and I think understates the practical bit.
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.
Worth separating two things that post #78 runs together.
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.
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.
Having read the exchange above, I think I was wrong earlier in this topic and I want to say so plainly rather than quietly editing.
The correction was fair and I had been repeating something I had not checked carefully enough.
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.
On post #82 — agreed on the reasoning, with one qualification.
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.
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.