Reading about receptor desensitisation and trying to work out which of the effects adapt over time and which do not, because people clearly experience both.
The bit I cannot resolve on my own is which effects tachyphylax and which persist, because the answer explains why tolerability improves while the appetite effect keeps working.
I have searched first, so if this is covered somewhere point me at it and I will read it.
SaraMom3 said:Reading about receptor desensitisation and trying to work out which of the effects adapt over time and which do not, because people clearly experience…
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.
Dr.LipidDallas said:PK/PD modeling for the pharmacology: understanding the pharmacokinetics helps optimize dosing.
Agreeing with Dr.LipidDallas, and the qualification matters more than the agreement. 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.
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Browse GL BiochemSaraMom3 said:Reading about receptor desensitisation and trying to work out which of the effects adapt over time and which do not, because people clearly experience…
Second this. The detail I would add is minor and it is already implied above.
Clinical perspective, offered as context rather than as advice.
Semaglutide structural biology relevant to the pharmacology: semaglutide is a 31-amino acid peptide with 94% homology to native GLP-1(7-36). Three key modifications enable its pharmacokinetic profile:
- Aib8 substitution: DPP-4 resistance (prevents enzymatic degradation)
- Arg34 substitution: improved chemical stability
- C18 fatty diacid at Lys26: albumin binding → long half-life
These three modifications transform a peptide with a 2-minute half-life (native GLP-1) into one with a 168-hour half-life (semaglutide). A masterclass in peptide engineering.