Bombesin

Bombesin is a peptide that was originally isolated from the skin of the European fire-bellied toad, Bombina bombina. It is a tetradecapeptide, meaning it consists of 14 amino acids. Bombesin and its related peptides are known for their role in various physiological processes, including the regulation of gastrointestinal and central nervous system functions.

Structure and Function

Bombesin is composed of the following amino acid sequence: pGlu-Gln-Arg-Leu-Gly-Asn-Gln-Trp-Ala-Val-Gly-His-Leu-Met-NH2. It is structurally related to other peptides such as gastrin-releasing peptide (GRP) and neuromedin B. Bombesin-like peptides bind to specific G protein-coupled receptors (GPCRs) on the surface of target cells, leading to a variety of biological effects.

Physiological Roles

Bombesin has several important physiological roles, including:

• **Stimulation of Gastric Acid Secretion**: Bombesin stimulates the release of gastrin, which in turn promotes the secretion of gastric acid in the stomach.
• **Regulation of Gastrointestinal Motility**: It influences the contraction and relaxation of smooth muscle in the gastrointestinal tract.
• **Thermoregulation**: Bombesin is involved in the regulation of body temperature.
• **Feeding Behavior**: It has been shown to suppress food intake, suggesting a role in the regulation of appetite.

Clinical Significance

Bombesin and its analogs have been studied for their potential use in diagnostic imaging and cancer therapy. Bombesin receptors are overexpressed in several types of cancer, including prostate cancer, lung cancer, and breast cancer. This makes bombesin analogs useful as targeting agents for radiolabeled compounds in positron emission tomography (PET) imaging and targeted radiotherapy.

Receptors

There are three main types of bombesin receptors:

• **BB1 (Neuromedin B Receptor)**: Primarily binds neuromedin B.
• **BB2 (Gastrin-Releasing Peptide Receptor)**: Binds gastrin-releasing peptide.
• **BB3 (Bombesin Receptor Subtype 3)**: The function of this receptor is less well understood, but it is believed to be involved in the regulation of energy balance and metabolism.

Research Applications

Bombesin and its analogs are used in research to study their effects on various physiological processes and their potential therapeutic applications. They are also used as tools to investigate the role of bombesin receptors in health and disease.

See Also

• Gastrin
• Gastrin-releasing peptide
• Neuromedin B
• G protein-coupled receptor
• Cancer therapy
• Diagnostic imaging