Mechanisms involved in colonic vasoconstriction and inhibition of motility induced by neuropeptide Y.

Neuropeptide Y (NPY) and noradrenaline are suggested to coexist as neurotransmitters in sympathetic neurons. The present study investigated the mechanisms involved in the colonic vasoconstriction and inhibition of motility induced by infusion of NPY and noradrenaline close i.a. Colonic blood flow was monitored using a drop recorder, and motility was registered by a volume recording device, both operating an ordinate writer. Colonic motility was stimulated either by electrical stimulation of the pelvic nerves (PNS; 4 Hz, 5 ms, 8 V) acting via enteric ganglia or by i.v. infusion of bethanechol (10 nmol kg-1 min-1) acting directly on muscarinic receptors on smooth muscle. With both types of motility stimulation, an immediate colonic vasodilatation was registered. Electrical stimulation of the lumbar colonic nerves (4 Hz, 5 ms, 8 V) induced colonic smooth muscle relaxation and vasoconstriction during continuous PNS (P less than 0.05). Colonic contraction induced by PNS (P less than 0.01) was dose-dependently reduced by NPY (50-400 pmol min-1; P less than 0.05-0.01) and noradrenaline (1000-6000 pmol min-1; P less than 0.05-0.01). Simultaneously, vasoconstriction was induced by both NPY and noradrenaline (P less than 0.01). Colonic contraction induced by infusion of bethanechol (P less than 0.01) was not inhibited by NPY (50-200 pmol min-1). However, at the highest dose (400 pmol min-1) the motility response was reduced (P less than 0.05). Similarly, noradrenaline only at the highest dose (6000 pmol min-1) reduced the contractile response (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)