2006级麻醉学研究生

1、Histamine,REPORTER: 2006级麻醉学研究生 向 凯,Histamine,Describe the physiology of histamine and clinical uses of histamine receptor antagonists Histamine is a biogenic amine involved in local immune responses as well as regulating physiological function in the gut and acting as a neurotransmitter.,This some what called histame hytpsensitivity,Histamine,Low MW amine Natural endogenous(内源的,内生的) substance Produces intense physiologic effects Locally Systemically Present in mast cells located Skin Lungs Gast

2、rointestinal (胃肠的)tract No CNS effects evident,Histamine: Synthesis,Occurs in tissues Decarboxylation(脱羧） of histidine（组氨酸） Stored in vesicles in a complex with heparin Stored histamine is released in response to antigen-antibody reactions,Histamine: Mechanism of Action,Released from storage cells by: Chemical insult Physical insult Mechanism involves a high intracellular（细胞内的） calcium concentration Release can be inhibited by high intracellular levels of cAMP Histamine acts via specific cell su

3、rface receptors,Histamine Effects on Organ Systems,Cardiovascular system Dilates fine vessels of the microcirculation Increasing capillary permeability（渗透性） Decrease in BP Capillary and arteriolar dilation Positive inotropic and chronotropic effects Direct H-2 receptor stimulation,Histamine Effects on Organ Systems,Extravascular smooth muscle H-1 receptors in bronchial smooth muscle Decreased lung capacity H-1 receptors in GI smooth muscle Spasmodic contractions,Histamine Effects on Organ System

4、s,H-2 receptors in parietal cells Increased gastric H+ secretion Evokes copious secretion of gastric fluid, pepsin, intrinsic factor of Castle Contains high concentration of H+ Increased gastric H+ secretion results from direct stimulating effect of histamine on parietal cell,Histamine Effects on Organ Systems,Dermal Classic wheal and flare response of skin Increased capillary permeability Increased vasodilatation（血管舒张） Immunologic Major mediator of type I hypersensitivity rxns,H-1 Receptors,Med

5、iate histamine-induced contraction of smooth muscle in GI and bronchi Mediate a delay in the conduction of cardiac impulses through the AV node,H-2 Receptors,Mediate histamine-induced secretion of gastric hydrogen ions (H+) Mediate increased myocardial contractility and HR H-2 receptors are present in the CNS,H-3 Receptors histamine,Function as autoreceptors Inhibit synthesis and release of hisamine,Histamine Physiologic Role,Increased gastric sections Allergic reaction & anaphylactic shock Tiss

6、ue repair & growth Neurotransmission Regulation of microcirculation,Histamine Untoward Effects,Vasodilatation producing Decrease BP Flushing Tachycardia（心动过速） Skin temperature increase HA / Visual disturbances Smooth muscle contractions Dyspnea Diarrhea,Risk Factors for Histaminoid Reactions,History of histaminoid reactions Reactions rare in children Reaction occur more frequently in young adults Peak incidence fourth decade Females affected more than males Neuromuscular blocking agents No evide

7、nce that anxious patients react more frequently Reactions to latex common with neural tube defects,Intra-operative Anaphylaxis,Intra-operative Anaphylaxis 70% Neuromuscular blocking agents 12.5% Latex 4.6% Colloids（胶体，胶质） 3.6% Hypnotic agents 2.6% Antibiotics,Tests for Histaminoid Reactions,Skin tests Intradermal skin tests Prick test Leucocyte histamine releasing test Allergen specific IGE,Skin test,Treatment,Aimed at modulating effects of released mediators and inhibiting mediator production a

8、nd release Stop the cause of histaminoid reaction Oxygen 100% Early intubation Epinephrineto manage hypotension, bronchospasm （支气管痉挛） and angioedema 1 ml of a 1:10000 solution IV, repeated every minute until a satisfactory clinical response,Treatment,Second therapy - antihistamines Catecholamine（儿荼酚胺） infusions Inhaled bronchodilators（支气管舒张药） Corticosteroids In the presence of sympathetic block by either blockers or regional anesthesia, reactions are usually refractory to treatment. High-dose do

9、pamine or other adrenoreceptor agonists may be required. Steroids ineffective in the acute reaction.,Histamine Receptor Antagonists,H1 and H2 receptor antagonists Do not inhibit release of histamine Attach to receptors and prevent responses mediated by histamine,H1 Receptor Antagonist,Bronchial smooth muscle Intestinal smooth muscle Small blood vessels Sensory impulses for itching Resemble histamine Contain a substituted ethylamine Unlike histamine Contain a tertiary amino group linked to two aromatic substituents,Anti-histame medicines,H1 Receptor Antagonists: Pharmacokinetics,Readily absorbed from GI tract Maximal plasma concentrations in 1 to 2 hours Elimination half-life is about 3.5 hours Extensive liver metabolism And there is still a lot of H-receptor Antagonists to make you known,If you are interested ,please contact me.,Thanks!,

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