HGH Fragment 176-191

HGH Fragment 176-191 (also written HGH Frag 176-191, hGH 176-191 or somatotropin 176-191) names a 16-residue peptide matching the last 16 amino acids of human growth hormone (hGH), residues 176 to 191. PubChem records the native sequence as FLRIVQCRSVEGSCGF, closed by a disulfide bond between its two cysteines (CID 16131230). The name is not used consistently: some papers and catalogs apply it to the tyrosine-substituted sequence YLRIVQCRSVEGSCGF (Habibullah et al., 2022), which the anti-doping literature identifies as AOD-9604 (Cox et al., 2015).

Published work on this end of the hormone comes mainly from rat studies of synthetic C-terminal fragments in the late 1970s and early 1980s, adipose tissue work on the closely related 177-191 sequence in the 1990s and early 2000s, and recent analytical chemistry.

Published work relevant to HGH Fragment 176-191 falls into five areas. Each summary below states the model used and, where it matters, which sequence was tested.

Identity and naming

Three related sequences appear under similar names. Native hGH 176-191 begins with phenylalanine. The 15-residue hGH 177-191 sequence lacks that first residue; its cyclic form was called AOD in a structural study, and a 177-191 peptide was designated AOD9401 in rat work (Ogru et al., 2000; Ng et al., 2000).

AOD-9604 adds a tyrosine to the start of 177-191, so it is also 16 residues long and differs from native 176-191 only at position one (Cox et al., 2015). A 2026 review lists AOD9604 and hGH 176-191 as a single entry (Dominikowski et al., 2026), while a 2026 doping-control method reports them as two separate analytes (Mazzarino et al., 2026).

Glucose and insulin studies in rats

The earliest work compared synthetic C-terminal fragments of different lengths in normal rats. hGH 172-191, 176-191, 177-191 and 178-191 produced a short-lived rise in blood glucose and a more sustained rise in plasma insulin, while 179-191 and 180-191 were inactive, and the authors concluded that activity needed both the core sequence and the correct physical configuration (Ng and Bornstein, 1978).

In isolated rat islets, hGH 177-191 potentiated glucose-induced insulin release without stimulating release on its own (Weerasinghe and Bornstein, 1978). Chain-shortening experiments in normal rats, using reduced and S-carbamidomethylated peptides, placed the insulin-antagonistic core within residues 178 to 190 (Wade et al., 1982).

Adipose tissue models built on the 177-191 sequence

Work in the 1990s and early 2000s moved to fat metabolism. In rat adipose tissue, synthetic hGH 177-191 showed antilipogenic activity matching intact growth hormone, with no significant change in glycerol release (Wu and Ng, 1993).

For the tyrosine analog, a mouse and cell study found that the peptide neither competed for the growth hormone receptor nor induced proliferation in receptor-transfected cells (Heffernan et al., 2001). These adipose results come from 177-191 or AOD-9604, not the native phenylalanine sequence, and they differ from the early rat studies in peptide form, duration and animal model, so the two sets of findings are not directly comparable.

Structure

Two-dimensional NMR of cyclic hGH 177-191 found type I beta-turns at Ser8-Val9-Glu10-Gly11 and Ser12-Cys13-Gly14-Phe15 of the peptide, and the authors reported partial structural similarity to the same region in the crystal structure of intact growth hormone (Ogru et al., 2000). The native 176-191 sequence carries the same two cysteines, recorded in PubChem as a ring between positions 7 and 14 (CID 16131230).

Cell culture, formulation and analytical work

A 2022 study loaded a peptide it called hGH fragment 176-191, specified as YLRIVQCRSVEGSCGF, into chitosan nanoparticles together with doxorubicin. Docking simulations predicted changes in doxorubicin binding to several breast cancer protein targets, and the dual-loaded particles showed greater antiproliferative activity against MCF-7 cells than particles carrying doxorubicin alone (Habibullah et al., 2022). That is one delivery study in one cell line, run with the tyrosine sequence.