Source comparison
Mechanism of Action: Pulsatile Stimulation vs Direct Replacement
MK-677 binds to ghrelin receptors (GHSR1a) in the hypothalamus and pituitary, mimicking the action of ghrelin. The endogenous 'hunger hormone' that also regulates growth hormone release. This binding triggers the release of growth hormone-releasing hormone (GH
This comparison does not assign a generated winner or score.
- MK-677 binds to ghrelin receptors (GHSR1a) in the hypothalamus and pituitary, mimicking the action of ghrelin. The endogenous 'hunger hormone' that also regulates growth hormone release. This binding triggers the release of growth hormone-releasing hormone (GHRH) from the hypothalamus, which then signals somatotroph cells in the anterior pituitary to secrete growth hormone in pulses that mirror natural circadian rhythm. Peak GH secretion occurs 60–90 minutes post-dose and follows a pulsatile pattern. This matters because growth hormone receptor sensitivity in peripheral tissues depends on pulsatile exposure; continuous elevation causes receptor downregulation and reduced IGF-1 conversion efficiency over time.
- Recombinant HGH injections deliver synthetic somatropin directly into subcutaneous tissue, where it enters systemic circulation within 3–6 hours. Serum GH levels rise immediately post-injection and remain elevated for 12–16 hours depending on dose. The liver converts circulating GH into IGF-1, which mediates most of growth hormone's anabolic effects: increased protein synthesis, enhanced lipolysis, and nitrogen retention. The critical distinction is feedback suppression: exogenous GH signals the hypothalamus to reduce endogenous GHRH secretion via negative feedback. MK-677 doesn't trigger this suppression because it works through the ghrelin pathway. A separate regulatory axis that doesn't inhibit GHRH.
- Subjects using MK-677 maintain baseline morning GH pulse amplitude even after 12 weeks of daily dosing, while those on exogenous HGH show near-complete suppression of endogenous secretion within two weeks. Recovery timelines differ accordingly: discontinuing MK-677 requires no PCT because endogenous production was never suppressed, whereas stopping HGH after prolonged use can take 4–8 weeks for pituitary function to normalize.