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GHRP-6

Growth Hormone Releasing Peptide-6, Growth hormone-releasing hexapeptide, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2

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1994 pubmed

Effect of growth hormone (GH)-releasing peptide (GHRP) on the release of GH from cultured anterior pituitary cells in cattle.

Soliman. E B EB; Hashizume. T T; Kanematsu. S S

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Key Findings

GHRP‑6 stimulates GH release from cultured bovine pituitary cells in a dose‑dependent manner, effective at concentrations of 10⁻¹¹ M and above.
When combined with GHRH, GHRP‑6 produces an additive increase in GH release, though the addition is not significantly greater than GHRH alone.
Somatostatin markedly inhibits GH release triggered by either GHRP‑6 or GHRH, but the inhibition is less pronounced when both peptides are used together.

Practical Outcomes

For biohackers, this study supports the idea that GHRP‑6 can directly boost GH without needing GHRH, but only at sufficient doses. It suggests that combining GHRP‑6 with a GHRH analog may not give a huge extra benefit, and that high somatostatin activity (e.g., from stress or certain foods) could blunt the GH surge. Use doses that achieve at least the low‑nanomolar range in the bloodstream and consider timing to avoid peak somatostatin levels.

Summary

In a lab study using cow pituitary cells, the peptide GHRP‑6 (His‑D‑Trp‑Ala‑Trp‑D‑Phe‑Lys‑NH2) was shown to make the cells release growth hormone (GH). The effect grew stronger with higher doses (from 10⁻¹¹ to 10⁻⁷ M) and was even bigger when combined with the natural GH‑releasing factor (GHRH). Both GHRP‑6 and GHRH‑induced GH release could be blocked by somatostatin, a hormone that normally suppresses GH.

Abstract

The effect of His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 (GHRP) on growth hormone (GH) release from cultured bovine anterior pituitary (AP) cells was studied in vitro with the interactive effects of GH-releasing factor (GRF: hpGRF (1-29)-NH2) and somatostatin (SRIF). The AP cells (5 x 10(4) cells per well) were incubated with media, and the media were changed 3 days after plating. After 3.5 days in culture, cells were incubated for 2 h with the peptides. GHRP stimulated GH release from cultured cells in a dose-related manner. At doses from 10(-11) to 10(-7) M GHRP, the amount of GH released was significantly greater than the controls (P < 0.05 to P < 0.001). The amounts of GH released at lower doses of GHRP (10(-14) to 10(-12) M) were not significantly different from the controls. GH concentrations after treatment with 10(-11) and 10(-7) M GHRP were 3.98 +/- 0.27 and 4.81 +/- 0.16 ng/ml, respectively. In experiments performed similarly, the 10(-7) M GHRH, GHRP, and combined treatment with GHRP plus GHRH increased GH 126, 57, and 139%, respectively (P < 0.001). The GH releasing effects of either GHRH alone or GHRP plus GHRH were significantly more potent than that of GHRP alone (P < 0.001). The additive effect was not significant when compared with GHRH alone. GH release induced by either GHRH or GHRP was significantly inhibited by SRIF (P < 0.01) compared with the untreated control. The inhibitory effect of SRIF in combined treatment with GHRP plus GHRH was significantly less than that of SRIF with GHRH or with GHRP (P < 0.01). The present study suggests that GH-releasing peptide (GHRP) induced GH release in cattle via a direct action on anterior pituitary cells in vitro.

Study Information

Provider

pubmed

Year

1994

DOI

10.1507/endocrj.41.585