Cardiovascular effects of neuropeptide Y in the nucleus tractus solitarius of rats: relationship with noradrenaline and vasopressin.

The central haemodynamic effects of neuropeptide Y (NPY), both alone and together with either noradrenaline (NA) or vasopressin (AVP), have been investigated by microinjecting synthetic peptide into the nucleus tractus solitarius (NTS) of anaesthetized rats. NPY alone elicited dose-dependent changes in blood pressure (BP) and heart rate (HR); 470 fmol inducing a pressor response, and 4.7 pmol a fall in BP. The hypotensive response to 20 nmol NA was significantly modified by both simultaneous and prior injection of an ineffective dose (47 fmol) of NPY. Prior injection of a similar dose of NPY also modified the NTS pressor effect of 10 ng AVP. A relationship between the action of AVP and NPY in the NTS was further indicated by the finding that prior injection of an ineffective dose of AVP (1 ng) reduced the hypotensive response to 4.7 pmol NPY, and by the demonstration of contrasting effects of 4.7 pmol NPY in AVP-deficient Brattleboro rats compared to parent strain LE rats. These results, taken together with the recent localization of NPY-like immunoreactivity in the NTS, suggest a role for NPY in central cardiovascular control. In addition, NPY has been shown to exhibit functional interactions with both an amine neurotransmitter and a neuropeptide present in the NTS of rats.