NITRIC-OXIDE MODULATES NEUROPEPTIDE-Y REGULATION OF ION-TRANSPORT IN MOUSE ILEUM

The possible involvement of nitric oxide in the regulation of intestin al ion transport induced by neuropeptide Y (NPY) was investigated by e valuating the effects of N-G-methyl-L-arginine (L-NMA), L-arginine and S-nitroso-N-acetylpenicillamine (SNAP) on NPY activity in mouse ileum mounted in Ussing chambers in vitro. Serosal NPY (10 nM) produced a s ustained decrease in basal transmural short circuit current (I-sc) and potential difference without altering the tissue conductance. Pretrea tment of tissues with L-arginine (3 mM), but not D-arginine (10 mM), b locked the NPY-mediated changes in I-sc. This L-arginine effect on NPY activity was reversed by L-NMA (3 mM), and not by N-G-methyl-D-argini ne (10 mM). The L-arginine effect on NPY activity was concentration-re lated with an A(50) (95% CL) value of 1.6 (0.9-2.3) mM. In contrast to L-arginine, L-NMA (1 mM) pretreatment of tissues produced an enhancem ent of NPY activity, resulting in a 3.8-fold leftward displacement of the NPY concentration-response curve; N-G-methyl-D-arginine was withou t effect. The effect of L-NMA on NPY activity was concentration-relate d with an A(50) (95% CL) value of 45.3 (23.2-68.8) mu M. Serosal appli cation of SNAP, a nitric oxide donor, produced a concentration-related decrease in basal I-sc and potential difference without altering tiss ue conductance with an A(50) (95% CL) value of 22.5 (11.1-40.5) mu M. Pretreatment of tissue with SNAP (100 mu M) reduced the NPY activity w ith rightward displacement of NPY concentration-response curve. Pretre atment of tissues with L-arginine also blocked the reduction of I-sc b y [D-Pen(2),D-Pen(5)]enkephalin (10-30 nM), H2N-Tyr-D-Ala-Phe-Glu-Val- Val-Gly-NH2 (10-30 nM) and somatostatin (0.3-1.0 mu M), but had no eff ect on norepinephrine (0.1-0.3 mu M)-induced decrease in mouse ileal I -sc. These results show that [fgc]l-arginine and SNAP block NPY-mediat ed changes in ion transport, suggesting that nitric oxide may play a r ole in the regulation of NPY-mediated ion transport in the mouse ileum .