Drugs online research references
J Hypertens Suppl. 1985 Dec;3 Suppl 3:S145-7.
Differences between exogenous and endogenous noradrenaline in the effects on vascular post-synaptic alpha 1- and alpha 2-adrenoceptors in man.
Jie K, van Brummelen P, Vermey P, Timmermans PB, van Zwieten PA.
Department of Nephrology, University Hospital Leiden, The Netherlands.
Effects of exogenous and endogenous noradrenaline, released by tyramine and lower body negative pressure (LBNP), on vascular post-synaptic alpha 1- and alpha 2-adrenoceptors have been compared in healthy volunteers. Intra-arterial (i.a.) infusions of noradrenaline and tyramine into the forearm were given in the presence of saline, of yohimbine and of doxazosin, and changes in forearm blood flow (FBF) were measured. Lower body negative pressure of -40 mmHg was applied without and with a continuous i.a. infusion of yohimbine and of doxazosin, and changes in FBF in both forearms were compared. Forearm blood flow was measured by venous occlusion plethysmography. Noradrenaline and tyramine reduced FBF dose-dependently and to the same extent. Both these vasoconstrictions were significantly reduced by yohimbine (P < 0.001 for both) as well as by doxazosin (P < 0.05 for noradrenaline and P < 0.001 for tyramine). The tyramine-induced vasoconstriction was more effectively reduced by doxazosin, whereas yohimbine reduced the noradrenaline-induced vasoconstriction more effectively. Lower body negative pressure reduced FBF in both forearms to the same extent. Doxazosin effectively inhibited the LBNP induced decrease in FBF (P < 0.05) whereas yohimbine had no effect (P > 0.05). These results are in accordance with a predominant intrasynaptic location of post-synaptic alpha 1-adrenoceptors and a predominant extrasynaptic location of post-synaptic alpha 2-adrenoceptors in human blood vessels.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2856814&dopt=Abstract
Clin Sci (Lond). 1985;68 Suppl 10:73s-75s.
Lack of differential inhibition by nifedipine of pressor responses induced by alpha 1- and alpha 2-adrenoceptor agonists and by angiotensin II in anaesthetized cats.
Alabaster VA, Solca AM.
The effect of nifedipine on pressor dose-response curves to phenylephrine, alpha-methylnoradrenaline and angiotensin II was determined in anaesthetized cats pretreated with propranolol and atropine. The selectivity of phenylephrine and alpha-methylnoradrenaline for postjunctional alpha 1- and alpha 2-adrenoceptors respectively was demonstrated by using the selective alpha 1-adrenoceptor antagonist doxazosin and the relatively selective alpha 2-adrenoceptor antagonist rauwolscine. Nifedipine infused intravenously produced a degree of inhibition of rises in diastolic blood pressure similar to that induced by all three agonists. It is concluded that alpha 1- and alpha 2-adrenoceptor activation induced by phenylethanolamine derivatives is equally dependent on extracellular calcium for vascular smooth muscle contraction. Antagonism of sympathetically mediated or angiotensin-induced vasoconstriction could contribute to the vasodilator effects of nifedipine.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2857622&dopt=Abstract
J Pharm Biomed Anal. 1999 Aug;20(4):621-30.
UV-spectrophotometry and square wave voltammetry at nafion-modified carbon-paste electrode for the determination of doxazosin in urine and formulations.
Fdez de Betono S, Arranz Garcia A, Arranz Valentin JF.
Departamento de Quimica Analitica, Facultad de Farmacia, Universidad del Pais Vasco/EHU, Vitoria, Spain.
By using several electrochemical techniques, the study of electroanalytical behaviour of antihipertensive Doxazosin at Nafion modified carbon paste electrode (NMCPE) has been carried out. The voltammetric peak is very pH dependent, reaching the maximum i(p) at pH 6.8 (Ep -0.17 V), the reduction process being quasi-reversible and fundamentally controlled by adsorption. A method based on the control of adsorptive preconcentration of the Doxazosin on the NMCPE, before its voltammetric determination, is proposed. The detection limit reached using square wave voltammetry (SWV) as redissolution technique was 2.33x10(-11) M and the variation coefficient at 2x10(-9) M level was 3.54%. A spectrophotometric study of Doxazosin has also been made and two waves at 244 and 329 nm (pH 1.7), were obtained. The wave at 329 nm changes its height and position with the pH, allowing the pKa determination (6.94+/-0.21) using different methods. The obtained detection limit was 0.5x10(-6) M, and the variation coefficient at 1.5x10(-5) M level was 0.99%. The UV spectrophotometric method is sufficiently accurate and precise to be applied in the Carduran tablets assay, while the voltammetric method (AdS-SWV) can in addition be used to determine the drug at trace level in human urine samples with good recoveries.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10704131&dopt=Abstract
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