histamine
histamine physiology, receptors and antihistamines
introduction
1st detected (with ACh) in ergot extracts as stimulants of uterus, but later both proved to be contaminants of ergot due to bacteria;
1st isolated from body 1927 in various tissues hence histamine;
Almost all mammalian tissues contain it - mainly stored in mast cells where it is synthesised from histidine via L-histidine decarboxylase & then store it in secretory granules along with heparin, ECF-A, NCF-A & certain enzymes which is exocytosed if i/cell. [Ca] is increased;
Turnover rate of histamine in granules is slow & when tissue depletion occurs, may take weeks for normal levels to return;
Histamine is rapidly made & continuously released in non-mast cell sites:
Histamine is metabolised to inactive metabolites (urine excreted) by:
physiologic roles:
mast cell response in immunity:
CNS neurotransmitter:
H1: reg. of drinking, T, ADH, BP, pain perception;
H3: presyn.reg. synth./release of his. in his.N terminals
Gastric histamine secretion ⇒ main factor in incr. parietal acid secret.(H2);
Epidermal release ⇒ pain/itch via stim. of nerve endings (H1);
Histamine Receptors & antagonists:
H1 receptor:
H2 receptors:
H3 receptors:
histamine.txt · Last modified: 2012/05/01 17:08 (external edit)