beta(3)-adrenoceptor deficiency blocks nitric oxide-dependent inhibition of myocardial contractility

Area of Science:

• Cardiology
• Molecular Biology
• Pharmacology

Background:

• Cardiac beta-adrenergic signaling enhances myocardial performance.
• Nitric oxide (NO) production, increased by beta-adrenergic activation, attenuates positive inotropy, suggesting negative feedback.
• In vitro studies implicate beta(3)-adrenoceptor stimulation in NO-mediated negative inotropy.

Purpose of the Study:

• To test the hypothesis that the beta(3)-adrenoceptor mediates beta-adrenergic activation of NO.
• To investigate the role of beta(3)-adrenoceptor in regulating cardiac contractility and NO signaling.

Main Methods:

• Utilized mice with homozygous beta(3)-adrenoceptor deletion mutations.
• Assessed myocardial performance and NO production under beta-adrenergic stimulation.
• Measured inotropic responses, NO synthase (NOS) inhibition effects, and cyclic guanosine monophosphate (cGMP) levels.

Main Results:

• Beta-adrenergic-stimulated inotropy was increased in beta(3)(-/-) mice compared to wild-type (WT).
• Similar hyper-responsiveness was observed in mice lacking endothelial NO synthase (NOS3).
• NOS inhibition augmented isoproterenol-stimulated inotropy in WT but not beta(3)(-/-) mice; isoproterenol increased myocardial cGMP in WT but not beta(3)(-/-) mice.

Conclusions:

• The beta(3)-adrenoceptor is responsible for beta-adrenergic activation of NO.
• Beta(3)-adrenergic signaling participates in NO-mediated negative feedback during beta-adrenergic stimulation.
• This pathway is crucial for regulating cardiac contractile reserve.