Neuropeptide Y (NPY) inhibits spontaneous contraction of the mouse atrium by possible activation of the NPY1 receptor.

Neuropeptide Y (NPY) causes various central and peripheral actions through activation of G-protein-coupled NPY receptors. Although a species-dependent difference in cardiac actions of NPY has been reported, the responses to NPY have not been examined in mice, widely used experimental animals. This study aimed to clarify the responses to NPY and the receptor subtype involved in the responses in mouse atrium. Neuropeptide Y caused negative inotropic and negative chronotropic actions in spontaneous beating right atria. Negative inotropic actions were more marked than negative chronotropic actions. Therefore, negative inotropic actions were studied in detail for evaluation of the NPY-induced cardiac actions in mouse atrium. Neuropeptide Y-induced negative inotropic actions were not affected by atropine but were abolished in the atria from pertussis toxin-treated mice. In isolated atrial preparations from reserpine-treated mice, NPY-induced negative inotropic actions were significantly attenuated. [Leu31, Pro34]-NPY, but not peptide YY, was effective in decreasing spontaneous contraction in atrial preparations. Although Y1 , Y2 , Y4 and Y5 receptor mRNAs were expressed almost equally in the brain, NPY1 receptor mRNA was dominantly expressed in the atrium. In conclusion, NPY caused negative inotropic and chronotropic actions through activation of the Y1 receptor in the mouse atrium. A high expression level of Y1 mRNA in the atrium suggests a functional role of NPY in the regulation of mouse cardiac contraction.