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Medical AI Inquiry: You was designed to assist in medical decision-making based on the provided user questions. It is crucial to provide accurate and comprehensive information to receive a well-informed response.  Labels: BACKGROUND, RESULTS. Meshes: Adrenergic beta-1 Receptor Antagonists, Adrenergic beta-Antagonists, Angiotensin II, Animals, Catecholamines, Collagen, Disease Models, Animal, Dogs, Drug Administration Routes, Epinephrine, Extracellular Space, Female, Heart, Hemodynamics, Male, Metoprolol, Mitral Valve Insufficiency, Myocardium, Neurons, Norepinephrine, Ventricular Function, Left.
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Does beta1-adrenergic receptor blockade attenuate angiotensin II-mediated catecholamine release into the cardiac interstitium in mitral regurgitation? Context: This study tested the hypothesis that beta1-adrenoreceptor blockade modulates the angiotensin II (Ang II)-evoked neural release of norepinephrine (NE) and epinephrine (Epi) into the cardiac interstitial fluid (ISF) space in experimentally induced mitral regurgitation (MR) in the dog. Normal dogs (n=8) were compared with dogs with MR of 2 (n=8) and 4 (n=6) weeks' duration and with dogs with MR treated with beta1-receptor blockade (RB; extended-release metoprolol succinate, 100 mg QD; MR+beta1-RB) that was started 24 hours after MR induction for 2 (n=6) and 4 weeks (n=8). Left ventricular end-diastolic dimension increased 20% as plasma Ang II levels increased >5-fold in both MR and MR+beta1-RB dogs at 2 and 4 weeks. Ang II infusion into the left atrium produced increases in ISF NE and Epi in normal dogs, which were further increased in 2- and 4-week MR dogs but were restored to normal in 4-week MR+beta1-RB dogs. Ang II infusion produced 4-fold increases in circulating NE and Epi in 2- and 4-week MR dogs that returned to normal in 4-week+beta1-RB dogs. Left ventricular angiotensin-converting enzyme activity and ISF Ang II were increased in 4-week MR dogs but were decreased in 4-week MR+beta1-RB dogs.
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beta1-RB decreases renin-angiotensin system sympathostimulation and activation by attenuating the Ang II-mediated NE and Epi release into the cardiac ISF and circulation and by decreasing left ventricular angiotensin-converting enzyme expression in the early phases of volume overload. Final Decision: yes