DISTRIBUTION AND FUNCTIONAL-EFFECTS OF NEUROPEPTIDE-Y ON EQUINE URETERAL SMOOTH-MUSCLE AND RESISTANCE ARTERIES

The distribution of neuropeptide Y (NPY)-immunoreactive (IR) nerves, a s well as the functional effects of NPY and the Y-1- and Y-2-receptor agonists, [Leu(31),Pro(34)]Npy and NPY(13-36), respectively, have been investigated in vitro in both visceral and arterial smooth muscle of the horse intravesical ureter. NPY-IR nerve fibres were widely distrib uted along the entire length of the ureter, although the intravesical part was the most richly innervated region, and the only one where NPY -IR ganglion cells were found. NPY(10(-7) M)) did not affect either ba sal tone or spontaneous rhythmic contractions of the isolated intraves ical ureter, but significantly enhanced the increases in both tone and frequency of phasic activity elicited by noradrenaline (10(-6) and 10 (-5) M). The Y-1-receptor agonist, [Leu(31),Pro(34)]Npy (10(-7) and 10 (-6) M) did not significantly alter either ureteral basal tone or the contractile activity induced by noradrenaline, whereas the Y-2-recepto r agonist, NPY(13-36) (10(-7) M), mimicked the potentiating effect of NPY on noradrenaline responses. In ureteral resistance arteries (effec tive lumen diameters of 130-300 mu m), NPY (10(-10) to 10(-7) M) elici ted concentration-dependent contractions, which were inversely correla ted with the arterial lumen diameter. Submaximal concentrations of NPY (10(-8) M) significantly increased the sensitivity of ureteral arterie s to noradrenaline. [Leu(31),Pro(34)]Npy (10(-10) to 10(-7) M), but no t NPY(13-36), induced a contractile effect of similar magnitude and po tency as those of NPY, and also potentiated noradrenaline responses. T he present results demonstrate a rich NPY-innervation in the intravesi cal ureter and reveal functional effects of the peptide enhancing moto r activity in both ureteral and arterial smooth muscles, although the receptors mediating such effects seem to be different. Thus, NPY poten tiates the phasic contractions and tone elicited by noradrenaline thro ugh Y-2-receptors, whereas it both contracts and potentiates noradrena line vasoconstriction in ureteral arteries via Y-1-receptors. (C) 1997 Elsevier Science B.V. All rights reserved.