Source comparison
Receptor Mechanisms: Ghrelin vs GHRH Pathway Activation
Ipamorelin binds type 1a growth hormone secretagogue receptors (GHS-R1a). The same receptor system activated by endogenous ghrelin. This binding triggers intracellular calcium mobilisation in pituitary somatotrophs, producing pulsatile growth hormone release t
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- Ipamorelin binds type 1a growth hormone secretagogue receptors (GHS-R1a). The same receptor system activated by endogenous ghrelin. This binding triggers intracellular calcium mobilisation in pituitary somatotrophs, producing pulsatile growth hormone release that mirrors the body's natural secretion rhythm. The selectivity is exceptional: Ipamorelin demonstrates minimal to no binding affinity for cortisol-stimulating ACTH receptors or prolactin-releasing pathways, which is why preclinical models show GH elevation without the cortisol spikes seen with earlier secretagogues like GHRP-6.
- Tesamorelin operates through an entirely different mechanism. As a synthetic analogue of growth hormone-releasing hormone (GHRH), it binds GHRH receptors on pituitary somatotrophs. The same receptors that respond to endogenous GHRH secreted by the hypothalamus. The critical structural modification is the addition of a trans-3-hexenoyl group at the N-terminus, which extends the peptide's half-life from minutes (native GHRH) to approximately 26 minutes in circulation. This modification allows once-daily dosing in research protocols while maintaining receptor selectivity.
- The downstream effects diverge significantly. Ipamorelin's pulsatile GH release more closely resembles physiological secretion patterns. Short bursts followed by baseline return. Tesamorelin's GHRH receptor activation produces more sustained GH elevation throughout the dosing interval, which appears to preferentially mobilise visceral adipose tissue through mechanisms not fully replicated by other GH-stimulating compounds. Research published in The Lancet demonstrated visceral fat area reductions of 15.2% with Tesamorelin versus 4.5% placebo over 26 weeks in lipodystrophy models. An effect size larger than most GH secretagogues produce.