Interaction of the novel GH secretagogue hexarelin with GHRH in regulating the secretion of GH by cultured human pituitary somatotrophinomas in vitro.
Liu. Q Q; Lei. T T; Liu. K K; Lin. W W; Adams. E F EF
Key Findings
- Hexarelin (20 nmol/L) strongly stimulates GH secretion in human pituitary tumor cells via a PKC‑dependent mechanism.
- (Ac‑Tyr1,D‑Arg2)-GRF(1‑29) does not inhibit hexarelin’s action but completely blocks the GH‑releasing effect of GHRH.
- Hexarelin alone does not change cAMP levels but enhances the cAMP‑mediated GH release caused by GHRH, indicating cross‑talk between their signaling pathways.
Practical Outcomes
- The study hints that hexarelin could boost GH and might work synergistically with GRF‑1‑29, but the experiments were done in vitro on tumor cells, not in people. For biohackers, this is an interesting mechanistic clue but not enough evidence to change dosing or combine these peptides without further human data.
Summary
In lab-grown human pituitary cells, the peptide hexarelin sharply increased growth hormone release by activating a PKC pathway, while the related peptide GRF‑1‑29 (a GHRH fragment) didn’t stop hexarelin but did block the normal GHRH effect. Hexarelin didn’t raise cAMP on its own but made GHRH’s cAMP‑driven boost bigger, showing the two peptides can interact.
Abstract
The effects of the novel GH-releasing hexapeptide, Hexarelin, on the secretion of GH in cultured human pituitary somatotrophinomas was further investigated. Hexarelin (20 nmol/L) strongly stimulated GH secretion, which could be reduced by phloretin, but not by RP-cAMPS, an inhibitor of protein kinase A (PKA). (Ac-Tyr1,D-Arg2)-GRF(1-29)-NH2 failed to block the effects of Hexarelin but completely abolished the stimulation of GH secretion exerted by GHRH. When added alone to somatotrophinoma cell cultures, Hexarelin had no effect on cAMP levels, but it potentiated the stimulatory effects of GHRH. These results demonstrated that Hexarelin could directly stimulate GH secretion by human pituitary somatotrophs PKC-dependently, which might be contributed to the activation of the PI transduction system. In addition, Hexarelin could interact with GHRH on the adenylyl cyclase system.
Study Information
pubmed
2000
10.1007/bf02887044