These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: Characterization of subtypes of alpha-2 adrenoceptors in the human brain.
    Author: Ordway GA, Jaconetta SM, Halaris AE.
    Journal: J Pharmacol Exp Ther; 1993 Feb; 264(2):967-76. PubMed ID: 8382286.
    Abstract:
    Radioligand binding studies have demonstrated that oxymetazoline has a high affinity for alpha-2A receptors, but lower affinities for alpha-2B and alpha-2C receptors. In contrast, prazosin has high affinity for alpha-2B and alpha-2C receptors, but relatively lower affinity for alpha-2A receptors. We exploited the respective selectivity of oxymetazoline and prazosin for alpha-2A and alpha-2B/2C adrenoceptors, respectively, to describe pharmacologically and to locate neuroanatomically alpha-2 adrenoceptor subtypes in the human brain. Competition curves for the inhibition of [3H]yohimbine binding by oxymetazoline and prazosin in homogenates of human caudate nucleus were fit best by a model assuming binding to two sites (P < .005). A concentration (CONCopt) of oxymetazoline and prazosin was calculated from these curves that would optimally antagonize binding of [3H]yohimbine to high-affinity sites, minimally inhibiting low-affinity binding. In the presence of CONCopt of prazosin, competition studies of remaining [3H]yohimbine binding in cerebral cortex revealed a rank order potency and potency ratios of compounds which were characteristic of alpha-2A receptors. In the presence of CONCopt of oxymetazoline, competition studies of remaining [3H]yohimbine binding in caudate revealed a rank order potency and potency ratios of compounds which were characteristic of alpha-2C receptors. The existence of a small population of alpha-2B adrenoceptors in the caudate could not be ruled out because slopes of competition curves of compounds which distinguish alpha-2B and alpha-2C adrenoceptors were shallow at oxymetazoline-insensitive sites. The percentages of [3H]yohimbine binding that were inhibited by the CONCopt of oxymetazoline and prazosin were determined in numerous brain regions. Oxymetazoline-sensitive binding of [3H]yohimbine predominated in most regions except for the caudate nucleus, where prazosin-sensitive binding was greatest.
    [Abstract] [Full Text] [Related] [New Search]