ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: A fraction enriched in capillaries has been prepared from the guinea pig cerebral cortex. The purity of this fraction was checked by light- and electron-microscopic examination and by its high enrichment in alkaline phosphatase and γ-glutamyl transpeptidase. In the capillary-rich fraction, the endogenous level of histamine was 1.9%’of that measured in the initial hornogenate. The histamine-synthesizing enzyme, I-histidine decarboxylase, and the metabolizing enzyme, histamine-N-methyltransferase, were barely detectable. In addition, histamine elicits a twofold stimulation in the accumulation of cyclic AMP in this capillary fraction with an EC50 of 5 γM. Agonists and antagonists of the two types of histamine receptors (H1 and H2) were used for the characterization of the receptors mediating this action: H2-receptor agonists were able to activate the adenylate cyclase with “relative potencies” similar to that found on typical H2-receptors, and cimetidine, a specific H2-receptor antagonist, competitively inhibited the response to histamine with a K1 value reflecting its interaction with a single population of H2-receptors. On the contrary, data obtained with H1-receptor agonists and antagonists reflect their interaction with H2-receptors rather than H1-receptors. Thus H2-receptors are involved in the activation of adenylate cyclase of the capillary fraction.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1980.tb09960.x
