GHRP-2 and GHRH combined infusion accelerates GH burst waveform and amplifies pulse mass 44-fold in men
Background
GH secretory dynamics are governed by a trio of hypothalamic signals: GHRH initiates pulses, GHRP amplifies them, and somatostatin (SS) terminates release. Despite decades of clinical use of GH secretagogues, exactly how these peptides shape the time course — not just the magnitude — of individual secretory bursts remained poorly characterised. Standard deconvolution models assumed a fixed burst waveform, leaving the question of whether secretagogues actively reshape pulse kinetics unanswered. Understanding waveform control matters for optimising GH replacement and stimulation protocols, since burst timing and shape influence downstream IGF-1 exposure and tissue anabolism.
Study Design
GHRH + GHRP-2 at maximally effective doses were delivered by continuous combined i.v. infusion to 12 healthy young eugonadal men; separate arms used bolus injection of each peptide after L-arginine pretreatment to suppress hypothalamic SS release. A mathematically verified variable-waveform deconvolution model was applied to intensively sampled GH time series to extract burst mode, mass, and number. An additional 10 young men with acute leuprolide-induced short-term hypogonadism underwent the same protocol to probe sex-steroid dependence.
Results
Baseline secretory-burst mode (time from onset to peak secretion) was 19 ± 0.69 min during saline infusion. Continuous dual stimulation with GHRH/GHRP-2 compressed this to 10.4 ± 3.0 min (p < 0.01); l-arginine/GHRH bolus reduced it to 14.6 ± 1.8 min (p < 0.025); and l-arginine/GHRH bolus in a third comparison yielded 15.0 ± 1.0 min (p < 0.01).
GHRH/GHRP-2 combined infusion amplified GH pulse mass 44-fold over saline (baseline: 2.2 ± 0.81 µg/L per h; p < 0.001), while l-arginine/GHRH arms produced 42-fold and 16-fold increases respectively (p < 0.001 each).
Pulse number and inter-pulse variability were unaffected by any secretagogue arm. Crucially, the 10 leuprolide-hypogonadal men showed comparable waveform compression and pulse-mass amplification, indicating these effects are independent of short-term sex-steroid milieu.
Key Findings
- GHRH/GHRP-2 infusion compressed secretory-burst mode from 19 ± 0.69 min to 10.4 ± 3.0 min (p < 0.01)
- GH pulse mass amplified 44-fold over saline (2.2 ± 0.81 µg/L per h) with GHRH/GHRP-2 (p < 0.001)
- L-arginine/GHRH bolus achieved 42-fold and 16-fold pulse-mass increases (p < 0.001 each)
- Pulse number and variability unchanged across all secretagogue conditions
- Waveform and mass effects reproduced in leuprolide-induced hypogonadal men, confirming sex-steroid independence
Why It Matters
Peptide secretagogues do not merely turn up GH output — they fundamentally reshape the kinetics of each burst, a finding with direct implications for dosing strategy. Clinicians and researchers using combined GHRH + GHRP-2 protocols should recognise that pulse timing shortens markedly, meaning sampling windows and biomarker assay timing need to account for a faster-rising, higher-amplitude peak. Combining GHRH with GHRP-2 delivered the greatest waveform compression and the largest mass increase (44-fold), making it the most pharmacodynamically potent secretagogue combination tested. The sex-steroid independence finding suggests these protocols are applicable regardless of short-term gonadal status, broadening potential clinical populations — including androgen-deficient patients — without requiring hormonal correction first.
