Cholecystokinin and the hormone concept.

Area of Science:

• Endocrinology
• Molecular Biology
• Cell Signaling

Background:

• The traditional definition of hormones relies on blood-borne transport, established by Bayliss and Starling in 1902.
• Recent discoveries reveal peptide hormones are produced and secreted by diverse cell types beyond endocrine glands.
• These hormones can exist in cell-specific molecular forms with varying activities.

Purpose of the Study:

• To review the historical development of the hormone concept.
• To advocate for an expanded definition of hormones to encompass all cell-activating messenger molecules.
• To highlight the multifaceted nature of cholecystokinin as a case study.

Main Methods:

• Historical literature review.
• Analysis of the evolving understanding of peptide hormone secretion and function.
• Case study analysis of cholecystokinin (CCK).

Main Results:

• The classical definition of hormones as solely blood-borne messengers is increasingly insufficient.
• Peptide hormones are released from various cells (neurons, immune cells, myocytes, etc.) and not just endocrine glands.
• Cholecystokinin exemplifies a molecule with diverse origins, forms, and functions, challenging the narrow hormone definition.

Conclusions:

• The concept of hormones should be broadened to include all messenger molecules activating target cells.
• This expanded definition should encompass various signaling pathways (endocrine, neurocrine, paracrine, etc.).
• It should also include diverse molecular activities (hormone, growth factor, neurotransmitter, adipokine, cytokine, etc.).