Demonstration of neuropeptide Y and its precursor in plasma and follicular fluid

The present investigation provides three lines of evidence for the presence of a pro-form of neuropeptide Y (NPY) in plasma and follicular fluid. First, by the demonstration of NPY-immunoreactive material of a size corresponding to the estimated mol wt of pro-NPY. Second, an antiserum specific for the C-terminal tyrosine amide of NPY and peptide YY does not react with this material. Third, it was possible to convert the pro-NPY extracted from plasma and follicular fluid using the protease, Endoproteinase-Lys C, to a NPY-immunoreactive form eluting slightly before NPY on a G-50 column. The size of the digested product was consistent with a cleavage of pro-NPY resulting in an immunoreactive species, NPY-Gly-Lys. Pro-NPY was also found in tissue culture media from the human neuroendocrine cell line SH-SY5Y. As in the case of plasma and follicular fluid, another NPY immunoreactive species eluted from a G-50 gel filtration column slightly before synthetic human NPY. Analysis of this material with an antibody directed against the tyrosine amide of NPY in combination with isoelectric focusing revealed that this peak consisted of at least two immunoreactive forms of NPY. In conclusion, at least three different forms of NPY immunoreactivity are likely to be present in plasma, follicular fluid, and cell tissue culture media; pro-NPY, a degradation form of pro-NPY, or a biosynthetic intermediate and NPY.