Synergistic pressor action of neuropeptide Y and norepinephrine in conscious rats.

The interaction of neuropeptide Y (NPY) and norepinephrine (NE) was studied in conscious unrestrained rats. Neuropeptide Y, administered intravenously (i.v.) in doses of 110 pmol/kg to 1.1 nmol/kg increased the mean arterial pressure (MAP) and decreased the heart rate (HR) in a dose-dependent way. The pressor effect of NPY (1.1 nmol/kg) was not attenuated by i.v. phentolamine in a dose of 3.1 mumol/kg. Norepinephrine infused at a rate of 89 nmol/kg per h, which had no effect on MAP, did not modulate the pressor effect of NPY. A pressor dose of NE infused at a rate of 266 nmol/kg per h significantly potentiated the pressor effect of NPY. Neuropeptide Y infused at a rate of 3.5 nmol/kg per h had no effect on MAP, and significantly potentiated the pressor effect of i.v. NE. It is concluded from these results that NPY could modulate the cardiovascular action of NE in physiological conditions.