inflammation, wounds and infections would never heal. Too little inflammation
could lead to progressive tissue destruction by the harmful stimulus (eg.
Bacteria) and compromise the survival of organism. In contrast, chronic
inflammation may lead to host of diseases such as hay fever, periodontitis,
atherosclerosis, rheumatoid arthritis, and even cancer (e.g., gallbladder carcinoma).
Inflammation is therefore normally closely regulated by the body.
is the body’s normal physiological response to injury. The cause of tissue
injury is attributed to trauma, autoimmune, microbial, heat and toxins
(chemicals). When tissue injury occurs, numerous substances are released by the
injured tissues, which cause changes to the surrounding uninjured tissues. Some
of the tissue products that cause the inflammatory reaction include: histamine
(which increases permeability, causes contraction of smooth muscle, and
constriction of the bronchioles), serotonin, lipid mediators (prostaglandins,
leukotrienes, and lipoxins and platelet-activator factor), bradykinin, products
of the complement system, products of the blood clotting system, and substances
released by the sensitized lymphocytes (lymphokines). These substances are the
messengers of the inflammation process, and have been viewed as areas of therapeutic
intervention. Collectively they are called autocoids (Dikshit et al., 2000). Autocoids are substances
released from the cells in response to various stimuli to elicit normal
physiological responses locally. An imbalance in the synthesis and release of
the autocoids contributes significantly to pathological conditions such as
inflammation, allergy, hypersensitivity and ischemia-reperfusion.
General Classifications of Autocoids
1. Biogenic amines – histamine, serotonin (5-HT)
2. Biogenic peptides – kinins (bradykinin, kallidin),
3. Small peptides – cytokines (e.g. interleukins,
chemokines, lymphokines, interferon, tumor necrosis factor) Cytokines are small
soluble proteins with low molecular weight. Their function is to act as
chemical messengers for regulation of innate and acquired immunity and
stimulate hematopoiesis. They are produced in just about all cells involved
with immunity, but in particular the T-helper cells.
4. Membrane derived – leukotrienes, prostaglandins,
thromboxane A2, platelet-activating factor, prostacyclin, lipoxins and
5. Endothelial derived – nitric oxide