GLP-1 Receptor Agonists: Mechanism of Action

Overview

GLP-1 (glucagon-like peptide-1) receptor agonists have become the most significant pharmacological advancement in metabolic medicine in decades. Semaglutide (Wegovy/Ozempic) and tirzepatide (Mounjaro/Zepbound) — a dual GIP/GLP-1 agonist — have demonstrated 15-22% total body weight loss in clinical trials, along with cardiovascular risk reduction.

Mechanism of Action

GLP-1 is a naturally occurring incretin hormone released by L-cells in the small intestine after eating. Synthetic GLP-1 RAs mimic and amplify this signal:

• Appetite Regulation: GLP-1 receptors in the hypothalamus and brainstem (nucleus tractus solitarius) modulate satiety signaling. Patients report earlier fullness and reduced food noise — the constant background preoccupation with eating.
• Insulin Secretion: GLP-1 RAs potentiate glucose-dependent insulin secretion from pancreatic beta cells. Crucially, this effect is glucose-dependent — insulin is only released when blood sugar is elevated, minimizing hypoglycemia risk.
• Gastric Emptying: GLP-1 RAs slow gastric emptying by 20-30%, contributing to postprandial satiety and glycemic control.
• Cardiovascular Effects: The SELECT trial demonstrated 20% reduction in MACE (major adverse cardiovascular events) with semaglutide, independent of weight loss. Mechanisms include reduced arterial inflammation, improved endothelial function, and decreased hepatic lipogenesis.
• Neuroprotection: GLP-1 receptors in the hippocampus and cortex are being studied for Alzheimer's and Parkinson's disease. Early data suggests anti-inflammatory and neuroprotective effects.

Tirzepatide: Dual Agonism

Tirzepatide uniquely activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptors. GIP receptors in adipose tissue enhance lipid metabolism, and the dual mechanism produced superior weight loss vs. semaglutide in the SURMOUNT trials (22.5% vs. 16.9% mean weight loss).

KAYU Protocol

KAYU prescribes FDA-approved brand-name GLP-1 agonists only (Wegovy, Mounjaro) — not compounded semaglutide, per current FDA enforcement. Dosing follows standard titration schedules with comprehensive metabolic labs (HbA1c, lipid panel, liver function, thyroid) at baseline, 3 months, and 6 months.