Receptor Selectivity and Endocrine Profiling of Ipamorelin: Characterization of Pulsatile Growth Hormone Release without Cortisol and Prolactin Stimulation

Principal Investigators: Raun, K., Hansen, B., Johansen, N., Thøgersen, H., Ankersen, M., & Andersen, P. H. (Novo Nordisk A/S, Denmark)

Methodology: In vivo testing evaluating the potency and selectivity of Ipamorelin against GHRP-2, GHRP-6, and native GHRH in conscious swine models. Plasma growth hormone (GH) levels were tracked alongside real-time monitoring of ACTH, cortisol, and prolactin profiles.

Key Findings: Ipamorelin stimulated a robust, dose-dependent surge in growth hormone with an $\text{ED}_{50}$ of $2.3\ \text{nmol/kg}$. Crucially, even at doses 200-fold higher than required for maximal growth hormone release, Ipamorelin induced no statistically significant change in plasma cortisol, ACTH, or prolactin lines. This completely decoupled growth hormone stimulation from the unwanted stress-axis side effects characteristic of older secretagogues.