Drugs online research references
Fundam Clin Pharmacol. 1997;11(1):63-7.
Further biochemical characterization of imidazoline binding sites from the human brainstem.
Greney H, Dontenwill M, Vonthron C, Bousquet P.
Laboratoire de Pharmacologie Cardiovasculaire et Renale, ERS 109 CNRS, Faculte de Medecine, Universite Louis Pasteur, Strasbourg, France.
Biochemical characteristics of imidazoline specific binding sites from the human brainstem were further investigated using [3H]idazoxan as radiolabeled ligand. The study of the interaction of [3H]idazoxan binding sites with heparin and lectins (soybean and lentil lectin) confirm the heterogeneity of these sites in the human brain. In fact, about 10-15% of [3H]idazoxan binding sites were retained by each of the three supports used, leading to the hypothesis that two populations of sites, with different biochemical characteristics, coexist in this tissue. A small proportion of [3H]idazoxan binding sites was retained on an affinity chromatography support consisting of a clonidine-derived Pharmalink column. The binding activity of these clonidine-eluted sites was markedly and dose-dependently improved by the addition of 'treated fall-through' fraction from the same column. On the other hand, this 'treated fall-through' fraction inhibited the binding activity detected in the solubilized human brainstem membranes. These results also suggest the existence of heterogeneous imidazoline specific binding sites in the human brainstem and the existence of endogenous factors able to discriminate between them.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9182078&dopt=Abstract
Nauchnye Doki Vyss Shkoly Biol Nauki. 1990;(6):85-96.
[The identification and characteristics of subpopulations of alpha 1-adrenergic receptors]
[Article in Russian]
Terman BI.
Rat liver and brain alpha 1-adrenergic receptors were purified 500 fold by successive chromatographic steps using heparin- and wheat germ agglutinin-agarose; an affinity matrix constructed by coupling CP85.224 (a derivative of prazosin) to affigel 102. It is shown that the existence in brain of an alpha 1-adrenergic receptor subpopulation, which is structurally distinct from that previously characterized. Chlorethylclonidine, irreversibly inactivates [3H] prazosin binding sites in partially purified membrane preparations of rat liver. Under identical conditions, only 50% of receptors are irreversibly inactivated. Computer modelling of data obtained from the competition by the alpha-antagonists, WB 4101 and phentolamine, for [3H] prazosin binding to partially purified preparations of rat liver is best fit by assuming a single low-affinity site for both ligands. However, the partially purified brain preparations indicates the presence of two affinity binding sites for these antagonists. Prior alkylation of brain receptors with chlorethylclonydyne results in the loss of the low-affinity phentolamine and WB4101 binding sites. These data provide evidence for the existence of a single receptor subpopulation (alpha 1b) in rat liver and for two subpopulations (alpha 1a and alpha 1b) in rat brain. The significance of these results in understanding the signal mechanisms which allow cellular responsiveness to alpha 1-adrenergic receptor agonists is discussed.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1976390&dopt=Abstract
J Pharmacol Exp Ther. 1977 Oct;203(1):56-63.
Facilitation of Chemoreceptor-induced reflex vasoconstriction by intravertebral arterial administration of clonidine.
Sybertz EJ, Zimmerman BG.
The influence of clonidine on the reflex vascular responses to stimulation of carotid body chemoreceptors and bilateral carotid occlusion was studied in morphine, chloralose-urethane anesthetized dogs. Bilateral carotid occlusion and intracarotid injection of nicotine (30 and 100 microgram) or sodium cyanide (200 and 500 microgram) elicited reflex vasoconstriction in the perfused gracilis muscle vascular bed. Infusion of clonidine (2-4 microgram/kg) into the vertebral artery significantly lowered blood pressure. Reflex vasoconstrictor responses to chemoreceptor stimulation were significantly enhanced after clonidine administration whereas reflex vasoconstrictor responses to carotid occlusion were markedly reduced. The facilitation of chemoreceptor reflex responses by clonidine was observed in dogs with intact or sectioned vagi and in animals in which the carotid arteries were perfused at constant blood flow. Inhibition of carotid occlusion responses by clonidine was observed in dogs with intact or sectioned vagi. Infusion of clonidine directly into the carotid arteries did not significantly alter responses to chemoreceptor stimulation. These experiments demonstrate that clonidine antagonizes the reflex vasoconstriction caused by carotid occlusion while potentiating the vasoconstriction elicited by chemoreceptor stimulation. The data suggest that clonidine exerts central actions which result in a facilitation of the chemoreceptor reflex and a simultaneously occuring hypotension which is probably due to an action on baroreceptor pathways.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=909057&dopt=Abstract
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