The article explores the presence of amyloid-like structures in secretory granules of the endocrine system, specifically focusing on peptide and protein hormones. Amyloids are typically associated with pathological conditions such as Alzheimer's disease and type II diabetes, but they can also have normal biological functions, as seen in fungal prions and the amyloid protein Pmel17. The study demonstrates that a significant number of peptide and protein hormones form amyloid-like cross-β-sheet structures in vitro and in vivo, particularly when glycosaminoglycans (GAGs) are present. These amyloid structures are stable and can release monomeric, functional hormones upon secretion, which is crucial for hormone release from secretory granules. The research also reveals that some hormone amyloids exhibit moderate toxicity, but this toxicity is likely mitigated by their encapsulation within the granules. The findings challenge the traditional view of amyloids as solely pathological and suggest a new perspective on their role in normal cellular physiology.The article explores the presence of amyloid-like structures in secretory granules of the endocrine system, specifically focusing on peptide and protein hormones. Amyloids are typically associated with pathological conditions such as Alzheimer's disease and type II diabetes, but they can also have normal biological functions, as seen in fungal prions and the amyloid protein Pmel17. The study demonstrates that a significant number of peptide and protein hormones form amyloid-like cross-β-sheet structures in vitro and in vivo, particularly when glycosaminoglycans (GAGs) are present. These amyloid structures are stable and can release monomeric, functional hormones upon secretion, which is crucial for hormone release from secretory granules. The research also reveals that some hormone amyloids exhibit moderate toxicity, but this toxicity is likely mitigated by their encapsulation within the granules. The findings challenge the traditional view of amyloids as solely pathological and suggest a new perspective on their role in normal cellular physiology.