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Evidence-based GLP-1 & peptide discussion since 2023
ForumsPharmacology & MechanismsGLP-1R expression map — looking for input

GLP-1R expression map — looking for input

HealthEcon_DC Mon, Jun 23, 2025 at 1:00 PM 13 replies 1,471 viewsPage 1 of 3
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HealthEcon_DC
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Jun 23, 2025 at 1:00 PM#1

Collecting this in one place because it comes up every few weeks and the answer is always assembled from scratch. It is about the pharmacology, and it is deliberately narrow — everything I am not confident about is marked as such.

What is actually established

The pharmacokinetics explain nearly every practical question asked here. Albumin binding above 99% slows clearance enough to make weekly dosing possible; a terminal half-life near a week means four to five weeks to steady state and therefore a four-week titration interval; subcutaneous bioavailability around 89% means injection site barely matters. Those three facts answer most timing questions before they are asked.

The condition it depends on

The adaptation point cuts both ways: tachyphylaxis to gastric emptying is why tolerability improves, and it is also why people who were relying on physical fullness feel the effect fade while the appetite effect is still working.

The practical version

Numbers worth memorising for this class: Tmax one to three days for the weekly peptides, terminal half-life about a week for semaglutide and about five days for tirzepatide, steady state at four to five half-lives, subcutaneous bioavailability high enough that site choice is irrelevant.

What I am not sure about

What I am trying to establish is which effects tachyphylax and which persist, because the answer explains why tolerability improves while the appetite effect keeps working. Tell me what I have not thought of.

— HealthEcon_DC · corrections welcome and will be edited into this post with credit
1 21NeuroNate
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LabKate
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Jun 23, 2025 at 2:23 PM#2
HealthEcon_DC said:
The pharmacokinetics explain nearly every practical question asked here.

Amycretin (AMY/GLP-1 dual agonist) emerging data relevant to the pharmacology: Phase 1 showed -13.1% body weight at only 12 weeks, the fastest trajectory ever seen for an anti-obesity agent[1].

Amylin receptor agonism enhances satiety signaling through the area postrema and reduces glucagon secretion. Combined with GLP-1R agonism, this dual mechanism may produce even greater efficacy than current agents.

Early-stage data — interpret with caution. But the trajectory is extraordinary.

References:
[1] Novo Nordisk investor presentation, September 2023.
50 20laura_annarbor, JenMemphis, pat_auckland and 47 others
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Dr.RaviCardio
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Jun 23, 2025 at 3:46 PM#3
HealthEcon_DC said:
The pharmacokinetics explain nearly every practical question asked here.

Pushing back on HealthEcon_DC here. The mechanism is more central than most summaries suggest. Receptor agonism in the arcuate nucleus activates POMC neurons and inhibits AgRP/NPY signalling, and the downstream MC4R pathway is the same one disrupted in monogenic obesity — convergent genetic evidence that the target is the right one. Peripherally there is glucose-dependent insulin secretion, glucagon suppression and delayed gastric emptying, but the gastric component largely adapts over months while the central effect persists, which is why the durable effect is appetite rather than fullness.

49 19mark_tokyo, hans_munich, jason_sac26 and 46 others
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Dr.AddMedPHL
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Jun 23, 2025 at 5:09 PM#4
Dr.RaviCardio said:
The mechanism is more central than most summaries suggest.

PK/PD modeling for the pharmacology: understanding the pharmacokinetics helps optimize dosing. Semaglutide:

  • Tmax: 24-72 hours post-injection
  • T½: ~168 hours (7 days) — enables weekly dosing
  • Steady state: reached at 4-5 weeks
  • Bioavailability (SubQ): ~89%
  • Volume of distribution: ~12.5L (primarily plasma)

The albumin binding (>99%) is the key pharmacological innovation — creating a sustained-release effect from a single injection. Previous GLP-1 agonists (exenatide) required BID dosing due to rapid clearance.

48 18TomFromTexas, mike.trainer_LA, sarah_nash92 and 45 others
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PharmHunterJen
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Jun 24, 2025 at 1:12 AM#5
LabKate said:
Amycretin (AMY/GLP-1 dual agonist) emerging data relevant to the pharmacology: Phase 1 showed -13.1% body weight at only 12 weeks, the fastest…

Same experience, arrived at from the opposite direction. Posting only so the count is not one.

Last edited: Jun 24, 2025 at 7:12 AM
47 17mike_mealprep, NicoleRaleigh, james_edin and 44 others
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