Neuropeptide Y contribution to the physiology of human sympathetic co transmission. Studies in saphenous vein biopsies

Background: It is known that the sympathetic varicosities co-store and co-r elease norepinephrine (NE) together with adenosine S-triphosphate (ATP) and neuropeptide Y (NPY). Aim: To describe the chemical characterisation of st ored and released NPY from the varicosities of sympathetic nerve terminals surrounding segments of the human saphenous vein, and the vasomotor activit y of rings electrically depolarized or contracted by the exogenous applicat ion of the co-transmitters. Material and methods: Saphenous vein tissues we re obtained from patients undergoing elective cardiac revascularization sur gery. Results: The chromatographic profile of NPY extracted from biopsies i s identical to a chemical standard of human NPY. Upon electrical depolarisa tion of the perivascular sympathetic nerve terminals, we demonstrated the r elease of NPY to the superfusion media, which did not exceed a 1% of its st ored content. The release of the peptide is sensitive to guanethidine, and to extracellular calcium, suggesting that the mechanism of its release is e xocytotic in nature. The electrically evoked suggesting that the mechanism of its release is exocytotic in nature. The electrically evoked release of NPY is dependent on the frequency and duration of the electrical pulses. Ph enoxybenzamine reduces the electrically evoked release of NPY. Exogenous ap plication of NE and ATP contract saphenous vein rings; the simultaneous app lication of NE plus ATP causes a synergic response, effect which is further potentiated by the joint co-application of 10 nM NPY. Conclusions: Present results highlight the role of NPY as a sympathetic co-transmitter in the r egulation of human vascular tone.