Effect of neuropeptide Y on α 2 ‐adrenoceptor‐mediated cardiovascular responses in the pithed rat

1 The effects of neuropeptide Y (NPY) on the cardiovascular responses induced by stimulation of pre‐ and postjunctional α 2 ‐adrenoceptors were studied in the pithed normotensive rat. 2 The increase in diastolic blood pressure induced by cumulative injection of xylazine (1–1000 μgkg −1 , i.v.) were potentiated by NPY (5 μg kg −1 ) but not affected by a lower dose (0.75 μg kg −1 ) of this peptide. 3 Xylazine (1–100 μg kg −1 ) inhibited in a dose‐dependent manner the tachycardia induced by continuous electrical stimulation (0.2 Hz, 2 ms, 60 V) of the spinal cord (C7‐Thl). 4 NPY (5 μg kg −1 but not 0.75 μg kg −1 ) enhanced the inhibitory effect of xylazine on the tachycardia induced by electrical stimulation without having any direct effect on heart rate. 5 These results suggest that there may be a positive interaction between NPY receptors, postjunctional α 2 ‐adrenoceptors and between NPY receptors and prejunctional α 2 ‐adrenoceptors in the cardiovascular system of the rat.