GHRP-6
Growth Hormone Releasing Peptide-6, Growth hormone-releasing hexapeptide, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2
GH-releasing peptide-6 overcomes refractoriness of somatotropes to GHRH after feeding.
McMahon. C D CD; Chapin. L T LT; Radcliff. R P RP; Lookingland. K J KJ; Tucker. H A HA
Key Findings
- Intravenous GHRP‑6 raises GH levels in a dose‑dependent way (1‑10 µg/kg).
- One hour after a meal, both GHRP‑6 and GHRH alone produce much smaller GH spikes than before eating.
- Combining a moderate dose of GHRP‑6 (3 µg/kg) with a low dose of GHRH (0.2 µg/kg) restores GH release to pre‑meal levels and makes it five times higher than GHRH alone after eating.
- GHRP‑6 stimulates GHRH release from hypothalamic tissue but does not change somatostatin release, indicating a dual action site.
Practical Outcomes
- For biohackers, pairing GHRP‑6 with a GHRH‑releasing peptide (or analog) can overcome the post‑meal GH dip, allowing robust GH spikes even when you’ve just eaten. A typical protocol might involve a modest GHRP‑6 dose (e.g., 100‑200 µg subcutaneously) taken with a low‑dose GHRH analog about 30‑60 minutes after a meal. This combination could enhance muscle growth, fat loss, and recovery without needing to fast. Timing and dosing should be adjusted based on individual response and safety monitoring.
Summary
After you eat, your pituitary cells that make growth hormone (GH) become less responsive to the usual signal (GHRH). This study shows that giving the synthetic peptide GHRP‑6 can restore and even boost that response, especially when used together with a low dose of GHRH. GHRP‑6 works both by directly stimulating the pituitary and by prompting the brain to release more GHRH, without affecting the GH‑blocking hormone somatostatin.
Abstract
After a meal, somatotropes are temporarily refractory to growth hormone-releasing hormone (GHRH), the principal hormone that stimulates secretion of growth hormone (GH). Refractoriness is particularly evident when free access to feed is restricted to a 2-h period each day. GH-releasing peptide-6 (GHRP-6), a synthetic peptide, also stimulates secretion of GH from somatotropes. Because GHRH and GHRP-6 act via different receptors, we hypothesized that GHRP-6 would increase GHRH-induced secretion of GH after feeding. Initially, we determined that intravenous injection of GHRP-6 at 1, 3 and 10 microg/kg body weight (BW) stimulated secretion of GH in a dose-dependent manner. Next, we determined that GHRP-6- and GHRH-induced secretion of GH was lower 1 h after feeding (22.5 and 20 ng/ml respectively) than 1 h before feeding (53.5 and 64.5 ng/ml respectively; pooleds.e.m.=8.5). However, a combination of GHRP-6 at 3 microg/kg BW and GHRH at 0.2 microg/kg BW synergistically induced an equal and massive release of GH before and after feeding that was fivefold greater than GHRH-induced release of GH after feeding. Furthermore, the combination of GHRP-6 and GHRH synergistically increased release of GH from somatotropes cultured in vitro. However, it was not clear if GHRP-6 acted only on somatotropes or also acted at the hypothalamus. Therefore, we wanted to determine if GHRP-6 stimulated secretion of GHRH or inhibited secretion of somatostatin, or both. GHRP-6 stimulated secretion of GHRH from bovine hypothalamic slices, but did not alter secretion of somatostatin. We conclude that GHRP-6 acts at the hypothalamus to stimulate secretion of GHRH, and at somatotropes to restore and enhance the responsiveness of somatotropes to GHRH.
Study Information
pubmed
2001
10.1677/joe.0.1700235