Drugs online research references
Clin Exp Pharmacol Physiol. 1989 Apr;16(4):329-32.
An in vitro study of interactions between doxazosin and enalaprilat at vascular alpha 1-adrenoceptors.
Tierney G, Marwood J, Stokes G.
Clinical Pharmacology Department, Royal North Shore Hospital, St Leonards, New South Wales, Australia.
1. Isolated perfused male Sprague-Dawley rat tail artery segments were used to investigate interactions between the alpha-1-adrenoceptor antagonist, doxazosin, and the angiotensin converting enzyme (ACE) inhibitor, enalaprilat, using phenylephrine (PE) as the alpha 1-adrenoceptor agonist. 2. In concentrations of up to 10(-5) mol/L, enalaprilat had no effect on arterial responses to PE. 3. Doxazosin produced a concentration-dependent competitive alpha 1-adrenoceptor antagonism, yielding a mean pA2 value of 8.72. 4. In the continuous presence of 10(-6) mol/L enalaprilat, doxazosin with a pA2 value of 9.10 was a 2.4-fold more potent alpha 1-adrenoceptor antagonist than in the absence of enalaprilat. 5. These results are interpreted to indicate that endogenously produced angiotensin II can modulate the activity of alpha 1-adrenoceptors in vascular smooth muscle.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2568203&dopt=Abstract
Clin Exp Hypertens A. 1989;11(5-6):1075-83.
Alpha blockers and vasodilating beta blockers--influence on factors involved in the pathogenesis of vascular disease in patients with hypertension.
Louis WJ, Drummer OH, Howes LG.
Department of Clinical Pharmacology & Therapeutics, Austin Hospital, Heidelberg, Vic, Australia.
Antihypertensive drugs that interact with adrenoceptors have certain advantages and disadvantages (on the treatment of hypertension). Alpha-1 antagonists such as prazosin have favorable effects on plasma lipids but may produce excessive postural falls in blood pressure, particularly following the initial dose. Recently developed alpha-1 antagonists (doxazosin, terazosin) have longer durations of action than prazosin, allowing less frequent administration. Beta blockers may be cardioprotective but in contrast to alpha-1 antagonists tend to have adverse effects on plasma lipids. Drugs with combined beta and alpha-1 blocking activity such as labetalol have favorable metabolic effects but postural hypotension remains a problem. Recently developed drugs with different alpha-1/beta blocking ratios that differ from labetalol may prove to be more popular clinically. Several beta blockers with vasodilator activity which is not due to alpha-1 blockade have also been developed. These drugs appear to have favorable metabolic effects similar to drugs with alpha-1 blocking activity, but do not cause postural hypotension.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=2571433&dopt=Abstract
unife.it
OBJECTIVE: Marked alterations have been demonstrated to occur in the platelet alpha2-adrenoceptors of patients with essential hypertension. The purpose of this study was to determine whether antihypertensive treatment with alpha-adrenergic blocker doxazosin or beta-adrenergic blocker propranolol can affect the affinity and the density of platelet alpha2-adrenoceptors in such patients. SUBJECTS AND METHODS: In two groups of 22 previously untreated, essential hypertensive patients, the mean affinity (Kd) and density (B(max)) of platelet alpha2-adrenoceptors were studied by [3H]-UK 14304 binding assays; the first assays were performed before any medication was begun, the second were performed after treatment for up to 13 weeks with doxazosin or propranolol. A third group of 22 healthy normotensive volunteers matched by age, sex and body mass index was used as control. RESULTS: Blood pressure did not differ significantly in the two hypertensive groups, and treatment with the two drugs resulted in closely similar, normal blood pressure levels. Kd and B(max) values were significantly higher in the two hypertensive groups than in controls. After treatment with propranolol the binding parameters did not change significantly, whereas after treatment with doxazosin Kd and B(max) returned to normotensive values. CONCLUSIONS: In previously untreated, essential hypertensive patients platelet alpha2-adrenoceptors have a lower affinity but a higher density than in normotensive subjects. Despite similar effects on blood pressure, the treatment with the alpha-adrenergic blocker doxazosin is followed by restoration of normal findings in the binding assays of platelet alpha2-adrenoceptors whereas the treatment with the beta-adrenergic blocker propranolol does not alter the Kd and B(max) values.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10694191&dopt=Abstract
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