EFFECT OF NEUROPEPTIDE-Y ON ALPHA-2-ADRENOCEPTOR-MEDIATED CARDIOVASCULAR-RESPONSES IN THE PITHED RAT

The effects of neuropeptide Y (NPY) on the cardiovascular responses induced by stimulation of pre- and postjunctional α2-adrenoceptors were studied in the pithed normotensive rat. The increase in diastolic blood pressure induced by cumulative injection of xylazine (1 - 1000 μg kg-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. 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). 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. These results suggest that there may be a positive interaction between NPY receptors, postjunctional α2-adrenoceptors and between NPY receptors and prejunctional α2-adrenoceptors in the cardiovascular system of the rat.