Source comparison
Mechanism of Action: GHRH Amplification vs Ghrelin Mimicry
CJC-1295 no DAC (also called Modified GRF 1-29) binds selectively to GHRH receptors on anterior pituitary somatotrophs. The same receptors activated by endogenous growth hormone-releasing hormone. The modification involves substituting four amino acids in the
This comparison does not assign a generated winner or score.
- CJC-1295 no DAC (also called Modified GRF 1-29) binds selectively to GHRH receptors on anterior pituitary somatotrophs. The same receptors activated by endogenous growth hormone-releasing hormone. The modification involves substituting four amino acids in the native GHRH sequence (positions 2, 8, 15, and 27), which protects the peptide from enzymatic degradation by dipeptidyl peptidase-IV (DPP-IV) without adding an albumin-binding Domain Antibody Component (DAC). This extends the active window from under 7 minutes (native GHRH) to approximately 30 minutes while preserving the pulsatile signaling pattern the hypothalamus naturally generates. When administered during an endogenous GH pulse. Typically 2–3 hours post-sleep onset or after intense exercise. CJC-1295 no DAC amplifies that pulse by increasing somatotroph cAMP production and calcium influx, which scales GH secretion 200–1000% above baseline for that specific pulse. The pulse completes, GH returns to baseline, and the next pulse
- MK-677 operates through an entirely different pathway: ghrelin receptor agonism. Ghrelin is the 'hunger hormone' secreted by gastric P/D1 cells, but it also binds to growth hormone secretagogue receptors (GHS-R1a) in the arcuate nucleus of the hypothalamus and directly on pituitary somatotrophs. MK-677 mimics this binding with higher affinity than endogenous ghrelin, stimulating both hypothalamic GHRH release and direct pituitary GH secretion simultaneously. Because MK-677 has a 4–6 hour half-life and downstream IGF-1 elevation persists for 24+ hours, it creates sustained receptor activation rather than discrete pulses. Research from the University of Virginia published in JCEM (1997) demonstrated that MK-677 25mg daily elevated mean 24-hour GH levels by 89% and IGF-1 by 79%. But this came at the cost of flattened GH pulsatility, with fewer distinct peaks and elevated trough levels throughout the circadian cycle.
- The mechanistic divergence matters for experimental design. If the research question involves studying natural GH pulse timing, amplitude modulation, or feedback sensitivity, CJC-1295 no DAC preserves those variables. If the goal is sustained anabolic signaling or chronic IGF-1 elevation to model pathological states, MK-677's override mechanism is more appropriate. One works with physiology; the other replaces it.