The effects of a continuous infusion of hexarelin on pulsatile growth hormone release, growth axis and galanin gene expression and on the response of the growth axis to growth hormone-releasing hormone.
Conley. L K LK; Brogan. R S RS; Giustina. A A; Wehrenberg. W B WB
Key Findings
- A short‑term (15 min) GH surge occurs after starting hexarelin infusion, but returns to baseline by 60 min.
- Continuous 6‑hour infusion does not change the normal pulsatile GH release pattern.
- Hexarelin markedly increases GH response to an external GHRH stimulus (57 ng/ml vs 21 ng/ml in controls).
- Hypothalamic galanin mRNA rises and GHRH mRNA falls after hexarelin infusion, while somatostatin and pituitary GH mRNA stay the same.
Practical Outcomes
- For biohackers, this study suggests that a constant low‑dose hexarelin drip is unlikely to raise overall GH levels, but it may prime the body to release more GH when combined with a GHRH trigger. Therefore, intermittent or combined dosing (hexarelin plus a GHRH analog) might be more effective than continuous infusion alone. However, the data are from rats, so human dosing and safety remain uncertain.
Summary
In rats, a 6‑hour steady drip of the peptide hexarelin (about 100 µg per hour) caused a quick spike in growth hormone that fell back to normal within an hour, and it didn’t change the normal pattern of GH pulses. However, after the infusion the animals responded much more strongly to a separate growth‑hormone‑releasing hormone (GHRH) challenge, and the brain’s levels of certain hormones that control GH (galanin went up, GHRH went down) were altered. This suggests hexarelin can make the GH system more sensitive to GHRH without directly raising baseline GH levels.
Abstract
The effect of a 6 hour continuous infusion of Hexarelin (100 micrograms/hour) on GH peak frequency, amplitude and duration, GH trough concentrations, the interval between successive peaks and the pituitary responsiveness to GHRH, as well as GH axis and galanin mRNA contents, were examined in conscious adult male rats. Plasma GH concentrations peaked within 15 minutes after the initiation of Hexarelin infusion, but returned to baseline levels by 60 minutes. No significant differences between Hexarelin and saline infused rats were noted for any of the parameters of pulsatile GH release analyzed. However, following a 6 hour infusion, rats treated with Hexarelin demonstrated a greater GH responsiveness to GHRH (delta GH: 57 +/- 16 ng/ml for Hexarelin infused; 21 +/- 7 ng/ml for saline infused; p < 0.05). Furthermore, the rats infused with Hexarelin demonstrated decreased GHRH and increased hypothalamic galanin mRNA contents as compared to the saline infused rats, while hypothalamic somatostatin and pituitary GH mRNA contents appeared unchanged. Rats infused with Hexarelin had lower pituitary galanin mRNA content than did the rats which were infused with saline. Collectively, these results suggest that Hexarelin may not act via alteration of somatostatin synthesis and that suppression of somatostatin's action at the pituitary can not be excluded. The current study also suggests that other hypothalamic pathways aside from those currently defined for the growth axis may be involved in the mechanism by which Hexarelin and the other GH-releasing peptides elicit GH release.
Study Information
pubmed
2000
10.1023/a:1009957015563