Pharmacology of Autacoids
Autacoids are local hormones with a brief duration of action, playing a role in various pathological conditions. Histamine, a potent tissue amine, acts on receptors to produce multiple effects on different systems. Learn about its mechanisms of action, pharmacological actions, and agonists.
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Presentation Transcript
Autacoids are are biological factors which act like local hormones, have a brief duration, and act near the site of synthesis The word autacoids comes from the Greek "Autos" (self) and "Acos" (relief, i.e. drug).
any imbalance in autacoids synthesis , release pathological conditions such as inflammation , allergy ,hypersensitivity and ischemia. autacoids like Histamine , serotonin ,prostaglandins and leukotrines
Histamine Histamine : It is a potent tissue amine widely distributed in plant and animal tissues and in the venoms of bees . histamine is a basic amine formed from histidine . stored in mast cell and basophiles.
Mechanism of action Mechanism of action : Histamine produces effect by acting on H1,H2,H3 ( and possibly H4 ) receptors on target cells . A-Stimulation of H1 receptors results in smooth muscle contraction (gut intestinal muscle ,bronchi ) ,increased vascular permeability , and mucous production
B-Activation of H2 receptors increases gastric acid production , cardiac stimulation and this effect is blocked by blockers such as cimetidine
Pharmacological action 1-Cardiovasicular system . Histamine produces dilatation of capillaries and venules accompanied by fall in blood pressure . 2-Smooth muscles: Histamine directly stimulates the smooth muscles of bronchi and uterus.
3-Exocrine glands . It is powerful stimulant of HCL secretion by the gastric mucosa 4-CNS :Histamine is acting by increasing the sensitivity of large cerebral areas .
Histamine agonists : -histamine :histamine injection is used to diagnose skin allergy . -betazole is used to stimulate gastric acid secretion.
Histamine antagonist : antihistamines A-Ethylenediamine derivatives . B-Ethanolamine derivatives : (phenothiazines ) ; it also possesses antitussive activity . C-Phenothiazine derivatives : -Promethazine
E-Piperazine derivatives cyclizine and meclizine . CNS depressant effects. F-inhibitors of mast cell e.g. cromolyn sodium . antihistamines:e.g.- cimetidine -Ranitidine .
Serotonin (5 HT ) Serotonin (5-hydroxytriptamine or 5-HT ) is synthesized from the amino acid tryptophan . it is stored in the intestine , the CNS , and mast cells . it is also found concentrated in blood platelets.
Pharmacological action : -effects respiratory volume and rate , bronchoconstriction , increase in motility of small intestine , vasoconstriction , vasodilatation of skeletal muscle beds , stimulation of sensory nerves , can contribute to pain responses .
Serotonin agonists : -buspirone ,sumatriptan: Serotonin antagonists : alosetron , Fluoxetine , sibutramine.
Eicosanoids : The eicosanoids ( prostaglandins , thromboxane , prostacyclin and leukotrienes ) . are found in the organism from arachidonic acid .
Platelets : - inhibits platelets aggregation - is a platelet activator - chemotaxis of eosinophils , monocytes , neutrophils -prostaglandins inhibit cellular and humeral immunity
Lung : -prostaglandins have mixed effect on bronchial muscle - inhibitors of thromboxane reduce bronchoconstrictive response - and - potent bronchoconstrictors
Uterus : Prostaglandins cause uterine contraction in pregnancy , clinically used as abortifacients. GIT : - and - inhibits gastric acid secretion . maintenance of the gastric mucosa stimulation of mucus secretion . - and - increase renal blood flow
Plasma kinnins Bradykinin named for its ability to produce a slow (brady ) contraction of the gut . Pharmacological effects of kinnins : 1-plasma kinnins are the most potent vasodilator autacoids
2-large arteries and most veins are contracted by bradykinnin. 3-increase capillary permeability , produce edema . 4-involved in pain responses . 5-contract bronchioles
Inhibitors of cyclooxygenase : 1-non steroidal anti-inflammatory drugs (NSAIDS) 2-inhibit the production of eicosanoids by inhibiting cyclooxygenase . Common pharmacological actions of NSAIDS: -analgesia . anti-inflammatory inhibition of platelet aggregation- anti-pyretic
Other autacoids agent Nitric oxide : Have many various action in the body involved vasodilatation , activation immune system , stimulate sexual and performance of male and regulate female reproductive system and other works in the tissue of the body
