Subtype of neuropeptide Y receptor in the heart of Wistar rat

Neuropeptide Y (NPY), a 36-amino acid peptide, is stored with noradrenaline (NA) in sympathetic nerves, particularly those which serve the cardiovascular regulation. However, little is known about the cardiac action of NPY. This study investigated the subtypes of neuropeptide Y receptors in the heart of Wistar rats. The isolated rat heart (Wistar rat, weighing 320- 350g) was suspended in a Langendorff apparatus. The Change of left ventricular pressure (LVP) was measured during the perfusion of different NPY receptor agonist and antagonist. Perfusion with NPY induced a decrease of LVP in a concentration-dependent manner from 1 nm to 5 nm (LVP decreased to 42.2 ± 0.9% of the basal tone at 5 nm). Treatment with NPY_3-36, the specific agonist of the NPY-Y₂ receptor, failed to produce a similar negative inotropic effect on isolated heart (LVP was 85.1 ± 6.8% of the basal tone, even at 5 nm). Perfusion with [Leu³¹, Pro³⁴] NPY, the specific agonist for the NPY-Y₁ receptor, did not modify the level of LVP except at a higher concentration (50 nm). In the presence of pertussis toxin (PTX) at the concentration (50 ng/mL) sufficient to inhibit Gi protein, the negative inotropic effect of NPY disappeared. Mediation of Gi protein in NPY-induced lowering of LVP can be considered. Otherwise, pretreatment with TrP³²NPY at concentration sufficient to block NPY-Y₁ and Y₂ receptors did not modify the negative inotropic action. NPY receptors in the heart of Wistar rat seem neither Y₁ nor Y₂ subtype and they are PTX-sensitive receptor, maybe the Y₃ subtype.