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MK-677 Increases Non-22kDa GH Isoforms — Growth Hormone Isn't One-Size-Fits-All

RPEP-008622003Svensson, J; Boguszewski, C L; Shibata, F; Carlsson, B; Carlsson, L M S; Bengtsson, B-A
Clinical TrialModerate evidence
The takeaway

Oral MK-677 altered the ratio of GH isoforms, increasing non-22kDa and 20kDa GH variants relative to standard 22kDa GH, suggesting GH secretagogues produce a different GH profile than exogenous GH injections.

Different GH types

MK-677 increased non-standard GH isoforms (20kDa, non-22kDa) — GH secretagogues don't just raise GH, they change the TYPES of GH produced

What the researchers found

MK-677 treatment increased the proportion of non-22kDa and 20kDa GH isoforms relative to total GH in obese subjects, demonstrating that GH secretagogues alter the GH isoform profile differently from exogenous GH replacement.

Why it matters

Different GH isoforms may have different biological effects (growth, fat metabolism, etc.). If MK-677 produces a unique GH isoform mix, its clinical effects may differ from standard GH injections in subtle but important ways.

How the study worked

Clinical trial substudy from the MK-677 body composition study. GH isoform analysis using size-exclusion HPLC and immunoassays in obese males during 8-week MK-677 treatment.

What this study cannot tell us

Isoform analysis in one study population. The clinical significance of altered isoform ratios is unknown.

How to read the evidence

Moderate evidence from a clinical study with specialized GH isoform analysis, revealing a previously unappreciated pharmacological dimension.

When this study was published

Published in 2003. GH isoform biology has been further studied but remains incompletely understood.

The bigger picture

GH pharmacology is more nuanced than total GH levels suggest. The isoform composition may determine which biological effects dominate — a dimension missed by standard GH assays.

Questions still open

  • Do different GH isoforms have different biological activities?
  • Does the altered isoform profile explain any unique MK-677 effects?
  • Should GH isoforms be monitored during GH secretagogue therapy?

Common questions

Is all growth hormone the same?
No — GH comes in multiple forms (isoforms) with potentially different effects. MK-677 changes which forms your body produces, creating a different GH mix than you'd get from standard GH injections.
Does this matter clinically?
Potentially. If certain GH isoforms favor fat burning while others favor growth, the isoform mix from MK-677 may produce different effects than expected based on total GH levels alone.

Read the original research

The effect of treatment with the oral growth hormone (GH) secretagogue MK-677 on GH isoforms.

Growth hormone & IGF research : official journal of the Growth Hormone Research Society and the International IGF Research Society, 13(1), 1-7

View on PubMed ↗

Citation

Svensson, J; Boguszewski, C L; Shibata, F; Carlsson, B; Carlsson, L M S; Bengtsson, B-A. (2003). The effect of treatment with the oral growth hormone (GH) secretagogue MK-677 on GH isoforms.. Growth hormone & IGF research : official journal of the Growth Hormone Research Society and the International IGF Research Society, 13(1), 1-7.