Presence of Neuropeptide-y in the rat seminal-vesicle and its effects on Noradrenaline-induced and nerve-induced contractions.

1 Immunohistochemical and functional studies have been performed to localize and determine the effects of neuropeptide Y (NPY) in the rat seminal vesicle. 2 An abundant presence of NPY-immunoreactive nerves, mainly concentrated in the smooth muscle layer of the seminal vesicle was found. Chronic 6-hydroxydopamine treatment (four doses of 50 mg kg(-1) i.p. on days 1, 2, 4 and 6; rats killed one week after the last injection) led to a large reduction but not abolition of the NPY-immunoreactivity. 3 NPY (1-250 nM) did not affect the resting tone of the seminal vesicle. 4 The seminal vesicle was contracted by electrical field stimulation (EFS) and by exposure to 5 mu M noradrenaline (NA). These contractions were abolished by phentolamine (1 mu M). Tetrodotoxin (0.5 mu M) abolished EFS-evoked contractions but did not affect NA-evoked contractions. 5 Seminal vesicles, from animals chronically-treated with reserpine (5 mg kg(-1) i.p. on days 1 and 2; rats killed on day 3), were contracted by NA but not by EFS. 6 NPY (0.25-250 nM), concentration-dependently, inhibited EFS-evoked contractions by up to 70% maximum inhibition. Contractions evoked by EFS with short trains of pulses were inhibited by NPY to a greater degree than those with longer trains. 7 NPY had no significant effect on NA-evoked contractions. 8 These data provide strong evidence that the motor transmission in rat seminal vesicle is predominantly if not exclusively, adrenergic. It is further concluded that a rich NPY-containing innervation is present in the smooth muscle layer of rat seminal vesicle. The primary effect of NPY is modulation of adrenergic motor transmission by a prejunctional inhibition of NA release.