Bradykinin

Bradykinin is a peptide that causes blood vessels to dilate (enlarge), and therefore causes blood pressure to fall. It is a part of the kallikrein-kinin system, which is a complex system of blood proteins that play a role in inflammation, blood pressure control, coagulation, and pain.

Structure and Function

Bradykinin is a nonapeptide, meaning it is composed of nine amino acids. The sequence of these amino acids is Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg. Bradykinin is produced from a precursor protein called kininogen through the action of the enzyme kallikrein.

Physiological Role

Bradykinin is involved in several physiological processes:

• **Vasodilation**: It causes the dilation of blood vessels, which leads to a decrease in blood pressure.
• **Pain**: Bradykinin is known to induce pain by stimulating sensory neurons.
• **Inflammation**: It plays a significant role in the inflammatory response by increasing the permeability of blood vessels, allowing immune cells to reach the site of infection or injury.
• **Smooth Muscle Contraction**: It can cause the contraction of smooth muscle in the bronchi and gastrointestinal tract.

Pathophysiology

Bradykinin is implicated in several pathological conditions:

• **Hereditary Angioedema**: A genetic disorder characterized by recurrent episodes of severe swelling. This condition is often due to a deficiency in C1 inhibitor, which normally regulates the production of bradykinin.
• **Septic Shock**: Excessive production of bradykinin can contribute to the severe drop in blood pressure seen in septic shock.
• **Chronic Pain**: Elevated levels of bradykinin are associated with chronic pain conditions.

Clinical Significance

Bradykinin levels can be influenced by certain medications:

• **ACE Inhibitors**: These drugs, used to treat high blood pressure, can increase bradykinin levels by inhibiting its breakdown, which can sometimes lead to a side effect known as ACE inhibitor-induced angioedema.
• **Kininase Inhibitors**: These are experimental drugs that aim to modulate the effects of bradykinin for therapeutic purposes.

See Also

• Kallikrein-kinin system
• Vasodilation
• Inflammation
• Pain
• Hereditary Angioedema
• ACE inhibitors