Source comparison
Mechanism of Action — GHRH Receptor Agonism vs Exogenous GH
Tesamorelin binds to GHRH receptors (GHRHR) on somatotroph cells in the anterior pituitary with approximately 100-fold greater potency than native human GHRH-44. The synthetic modification at positions 2, 27, 29, and 44 extends the peptide's half-life from 7 m
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- Tesamorelin binds to GHRH receptors (GHRHR) on somatotroph cells in the anterior pituitary with approximately 100-fold greater potency than native human GHRH-44. The synthetic modification at positions 2, 27, 29, and 44 extends the peptide's half-life from 7 minutes to roughly 38 minutes while maintaining receptor selectivity. Once bound, the GHRHR activates adenylyl cyclase via Gs protein coupling, increasing intracellular cAMP and triggering calcium-dependent exocytosis of growth hormone from secretory granules. This process is pulsatile. Tesamorelin administration mimics the natural ultradian rhythm of GH secretion (8–12 pulses per 24 hours) rather than creating sustained supraphysiologic levels.
- The critical downstream effect is hepatic IGF-1 synthesis. GH stimulates IGF-1 production in hepatocytes via the JAK2-STAT5 signaling pathway, and IGF-1 exerts negative feedback on both hypothalamic GHRH release and pituitary GH secretion. Exogenous GH bypasses this feedback entirely. When you inject somatropin, IGF-1 rises but the pituitary keeps producing GH because the hypothalamic signal never stopped. Tesamorelin respects the feedback loop: if IGF-1 climbs too high, the pituitary reduces GH output automatically. This is why tesamorelin trials report mean IGF-1 elevations of 1.5–2.0 times baseline, while exogenous GH can push IGF-1 to 3–4 times baseline if dosed aggressively.
- Visceral adipose tissue reduction occurs because GH and IGF-1 upregulate hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) in visceral adipocytes. These are the rate-limiting enzymes for lipolysis. VAT is more metabolically active and insulin-sensitive than subcutaneous fat, so it responds more dramatically to GH-mediated lipolysis. The COSMIC-1 trial (326 HIV-positive patients with abdominal VAT >150 cm²) demonstrated 15.2% mean VAT reduction at 26 weeks on tesamorelin 2mg daily vs 4.4% placebo. Subcutaneous fat remained largely unchanged, which is the clinical signature distinguishing GHRH agonists from caloric restriction or GLP-1 therapy.