kininins

Kininins are a group of peptides that play a crucial role in the renin-angiotensin-aldosterone system (RAAS) and the kallikrein-kinin system (KKS). They are derived from the cleavage of high-molecular-weight kininogens (HMWKs) by the enzyme kallikrein. There are two main types of kininins: bradykinins and tachykinins.

Bradykinins, such as bradykinin-1, are vasodilators and increase vascular permeability, leading to edema and inflammation. They are involved in the body's response to injury and infection. Bradykinins also stimulate smooth muscle contraction, which can cause bronchoconstriction in the lungs.

Tachykinins, including substance P and neurokinin A, are neurotransmitters and neuromodulators. They are involved in pain transmission, inflammation, and immune responses. Tachykinins can also cause smooth muscle contraction and vasodilation.

Kininins are released in response to tissue damage, infection, and inflammation. They act locally to mediate these responses, but they can also be released into the circulation and act on distant organs. The actions of kininins are regulated by their degradation by enzymes such as angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP).

Kininins have been targeted for therapeutic purposes due to their roles in inflammation and pain. Inhibitors of kinin degradation, such as ACE inhibitors and NEP inhibitors, are used to treat conditions like hypertension and heart failure. However, these inhibitors can also have side effects, such as cough and increased risk of infection, due to the role of kininins in the immune system.