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The beta 1 hyperselectivity in beta-blocker treatment.

Abstract

Coronary heart disease (CHD) is the most common cause of death in Western industrialized countries. CHD is more common in individuals with clustering of coronary risk factors, e.g., hypertension and blood lipid abnormalities. There is a good rationale for the use of beta-blockers for prevention of myocardial infarction (MI) in high-risk groups, as beta-blockade decreases myocardial oxygen consumption and, by decreasing turbulent blood flow patterns, reduces endothelial shear forces, thus making plaque rupture (and the ensuing thrombotic events) less likely. Clinical trial data have shown beta-blockade to be effective in the prevention of cardiovascular end points. In both younger and older hypertensive patients there is a significant reduction in the incidence of stroke and in younger hypertensive patients there is about a 15% reduction in MI. Left ventricular hypertrophy (particularly by ECG) is significantly diminished. In secondary prevention of MI there is about 15% reduction after early and 25-30% reduction after late intervention with beta-blockers given post-MI. In both stable and unstable angina, beta-blockade appears to be beneficial not only in improvement of symptoms but also in prevention of hard cardiovascular end points. There are also promising data suggesting that beta-blockade is useful in endothelial protection and atheroma prevention, and benefits patients with hypertrophic cardiomyopathy and heart failure. beta-Blockers have evolved from early nonselective agents, e.g., propranolol, to modern highly beta 1-selective agents, e.g., bisoprolol. beta 1-Blockade is the essential element that leads to the above cardiovascular benefits in addition to improving the quality of life (similar to angiotensin-converting enzyme inhibitors).

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BibTeXRIS

J M Cruickshank. 1995. The beta 1 hyperselectivity in beta-blocker treatment.. https://doi.org/10.1097/00005344-199525001-00008

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beta1 antagonist and beta2 agonist, celiprolol, restores the impaired endothelial dependent and independent responses and decreased TNFalpha in rat with type II diabetes.

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Adrenergic beta-1 Receptor Antagonists↗

Cardiovascular effects produced by activation of GABA receptors in the rostral ventrolateral medulla of conscious rats.

The rostral ventrolateral medulla (RVLM) has been proposed as a region playing a major role in the tonic and reflex control of sympathetic vasomotor activity and blood pressure. Pharmacological activation of GABA(A) receptors with muscimol in the RVLM of anesthetized rats results in a large fall in mean arterial pressure (MAP), heart rate (HR) and sympathetic activity. In this study we evaluated the effects of activation of GABA receptors in the RVLM of conscious, freely moving rats. Bilateral microinjections of muscimol into the RVLM of conscious rats produced a large fall in MAP (-38+/-4 mm Hg, n=7) when compared with saline injections (NaCl 0.9%, 7+/-1 mm Hg, n=4). The decrease in MAP evoked by muscimol was accompanied by a significant increase in HR (muscimol 69+/-13 bpm vs. vehicle -33+/-12 bpm, P<0.05), an effect that was completely abolished by beta1 adrenergic receptor blockade. Conversely, bilateral microinjections of GABA(B) agonist, baclofen, evoked a pressor response, but in this case, the increase was not significantly different from that evoked by vehicle injections. These results 1) indicate that GABA(A) receptors have a powerful influence on the resting activity of RVLM neurons in conscious rats; 2) indicate that a compensatory sympathetic-mediated tachycardia is present after inhibition of RVLM neurons in conscious rats; 3) confirm and extend previous findings showing that RVLM neurons are critical for blood pressure maintenance even in normal non-anesthetized conditions.

Adrenergic beta-1 Receptor Antagonists↗

Role of Tyr(356(7.43)) and Ser(190(4.57)) in antagonist binding in the rat beta1-adrenergic receptor.

Site-directed mutagenesis and photoaffinity labeling experiments suggest the existence of at least two distinct binding orientations for aryloxypropanolamine competitive antagonists in the beta-adrenergic receptor (beta-AR), one where the aryloxy moiety is located near transmembrane alpha-helix 7 (tm 7) and another where it is near tm 5. To explore a hydrophobic pocket involving tms 1, 2, 3, and 7 for potential aryloxy interaction sites, we selected Tyr(356(7.43)) and Trp(134(3.28)) in the rat beta(1)-AR for site-directed mutagenesis studies. Ser(190(4.57)) was also investigated, as the equivalent residues are known antagonist interaction sites in the muscarinic M(1) and the dopamine D(2) receptors. Binding affinities (pK(i)) of a series of structurally diverse aryloxypropanolamine competitive antagonists were determined for wild type and Y356A, Y356F, W134A, and S190A mutant rat beta(1)-ARs stably expressed in Chinese hamster ovary cells. To visualize possible antagonist/receptor interactions, the compounds were docked into a three-dimensional model of the wild-type rat beta(1)-AR. The results indicate that Tyr(356(7.43)) is an important aromatic interaction site for five of the eight competitive antagonists studied, whereas none of the compounds appeared to interact directly with Trp(134(3.28)). Only two of the competitive antagonists interacted with Ser(190(4.57)) on tm 4. Overall, the results extend our understanding of how beta(1)-AR competitive antagonists bind to the hydrophobic pocket involving tms 1, 2, 3, and 7; highlight the importance of Tyr(356(7.43)) in this binding pocket; and demonstrate the involvement of tm 4 in competitive antagonist binding.

Adrenergic beta-1 Receptor Antagonists↗