| histamine h1 antagonists | Drugs that selectively bind to but do not activate histamine h1 receptors, thereby blocking the actions of endogenous histamine. Included here are the classical antihistaminics that antagonise or prevent the action of histamine mainly in immediate hypersensitivity. They act in the bronchi, capillaries, and some other smooth muscles, and are used to prevent or allay motion sickness, seasonal rhinitis, and allergic dermatitis and to induce somnolence. The effects of blocking central nervous system h1 receptors are not as well understood. (12 Dec 1998) |
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| histamine h2 antagonists | Drugs that selectively bind to but do not activate histamine h2 receptors, thereby blocking the actions of histamine. Their clinically most important action is the inhibition of acid secretion in the treatment of gastrointestinal ulcers. Smooth muscle may also be affected. Some drugs in this class have strong effects in the central nervous system, but these actions are not well understood. (12 Dec 1998) |
| histamine headache | A term used to describe a headache that is typified by constant, unilateral pain around the eye, with onset usually within 2-3 hours of falling asleep. Can be accompanied by a blocked nasal passage, runny nose, and-or tearing. One may also notice facial flushing, ptosis (dropping eyelid), facial swelling and constriction of the pupils. (27 Sep 1997) |
| histamine liberators | Substances that cause the release of histamine from mast cells or basophils. (05 Mar 2000) |
| histamine n-methyltransferase | <enzyme> An enzyme that catalyses the transfer of a methyl group from s-adenosylmethionine to histamine, forming n-methylhistamine, the major metabolite of histamine in man. Chemical name: S-Adenosyl-L-methionine:histamine N-tele-methyltransferase Registry number: EC 2.1.1.8 (12 Dec 1998) |
| histamine shock | The shock state produced in animals by the injection of histamine; characterised by bronchiolar spasm in the guinea pig and constriction of hepatic veins in the dog. (05 Mar 2000) |
| acidophilic leukocyte | A polymorphonuclear leukocyte characterised by many large or prominent, refractile, cytoplasmic granules that are fairly uniform in size and bright yellow-red or orange when treated with Wright's or similar stains; the nuclei are usually larger than those of neutrophils, do not stain as deeply, and characteristically have two lobes (a third lobe is sometimes interposed on the connecting strand of chromatin); these leukocyte's are motile phagocytes with distinctive antiparasitic functions. Synonym: acidophilic leukocyte, eosinocyte, eosinophil, eosinophile, oxyphil, oxyphile, oxyphilic leukocyte. (05 Mar 2000) |
| agranular leukocyte | <haematology> A general, non-specific term frequently used with reference to lymphocytes, monocytes, and plasma cells; although the cytoplasm of a lymphocyte or monocyte contains tiny granules, it is nongranular in comparison with that of a neutrophil, basophil, or eosinophil. See: leukocyte. Synonym: agranular leukocyte. (05 Mar 2000) |
| automated differential leukocyte counter | An instrument using digital imaging or cytochemical techniques to differentiate leukocytes. (05 Mar 2000) |
| basophilic leukocyte | A polymorphonuclear leukocyte characterised by many large, coarse, metachromatic granules (dark purple or blue-black when treated with Wright's or similar stains) that usually fill the cytoplasm and may almost mask the nucleus; these leukocyte's are unique in that they usually do not occur in increased numbers as the result of acute infectious disease, and their phagocytic qualities are probably not significant; the granules, which contain heparin and histamine, may degranulate in response to hypersensitivity reactions and can be of significance in general inflammation. Synonym: basocyte, basophilocyte, mast leukocyte. (05 Mar 2000) |
| receptors, leukocyte-adhesion | Family of proteins associated with the capacity of leukocytes, including lymphocytes, monocytes, and neutrophils, to adhere to each other and to certain substrata, e.g., the c3bi component of complement. Members of this family are the lymphocyte function-associated antigen-1 (lfa-1), the macrophage-1 antigen (mac-1), and the antigen p150,95 or p150,95 leukocyte adhesion protein. They all share a common beta-subunit which is the CD18 antigen. All three of the above antigens are absent in inherited leukocyte-adhesion deficiency syndrome, which is characterised by recurrent bacterial infections, impaired pus formation, and wound healing as well as abnormalities in a wide spectrum of adherence-dependent functions of granulocytes, monocytes, and lymphoid cells. (12 Dec 1998) |
| mast leukocyte | A polymorphonuclear leukocyte characterised by many large, coarse, metachromatic granules (dark purple or blue-black when treated with Wright's or similar stains) that usually fill the cytoplasm and may almost mask the nucleus; these leukocyte's are unique in that they usually do not occur in increased numbers as the result of acute infectious disease, and their phagocytic qualities are probably not significant; the granules, which contain heparin and histamine, may degranulate in response to hypersensitivity reactions and can be of significance in general inflammation. Synonym: basocyte, basophilocyte, mast leukocyte. (05 Mar 2000) |
| globular leukocyte | A type of wandering cell with a small, round nucleus found in the epithelium and lamina propria of the intestinal mucosa of many animals; its cytoplasm contains large eosinophilic globules or droplets. (05 Mar 2000) |
| granular leukocyte | Any one of the polymorphonuclear leukocyte's, especially a neutrophilic leukocyte. See: granulocyte, basophilic leukocyte, eosinophilic leukocyte. (05 Mar 2000) |
| chemotaxis, leukocyte | The movement of leukocytes in response to a chemical concentration gradient or to products formed in an immunologic reaction. (12 Dec 1998) |