Coinjections of NPY(1–36) or [Leu31,Pro34]NPY with adrenaline in the nucleus tractus solitarius of the rat counteract the vasodepressor responses to adrenaline

The cardiovascular effects of adrenaline microinjected alone or together with neuropeptide Y (NPY) receptor agonists into the nucleus tractus solitarius (Sol) of the anaesthetized rat have been investigated in order to evaluate NPY/adrenergic receptor interactions. In the dose range 0.05-20 nmol, adrenaline microinjected unilaterally into the Sol produced significant dose-related reductions in mean arterial blood pressure and heart rate. The vasodepressor action of a close to ED50 dose of adrenaline (0.5 nmol) was significantly counteracted by a threshold dose of NPY (1-36) (1 pmol) and of the NPY Y1 receptor agonist [Leu31,Pro34]NPY (2.5 pmol) microinjected into the Sol, but not by a threshold dose of NPY(13-36)(50 fmol), a selective Y2 receptor agonist. The present study provides evidence for an antagonistic NPY Y1/adrenergic receptor interaction in the Sol of the rat, involved in cardiovascular regulation.