Levels and molecular properties of secretoneurin-immunoreactivity in the serum and urine of control and neuroendocrine tumor patients

We have determined the levels of secretoneurin (SN), a novel 33-amino acid neuropeptide belonging to the class of chromogranins, in the serum and urin e of healthy subjects and patients suffering from various tumors. SN serum levels averaged 22.1 +/- 1.1 fmol/ml. They were 5-fold higher in younger ch ildren and then declined continuously. SN levels were positively correlated with serum creatinine, suggesting an influence of renal function on the cl earance of SN from the serum. In the urine 80.0 fmol/ml SN was present. In patients with endocrine tumors like gut carcinoids, endocrine pancreatic tumors, oat cell lung carcinomas, and pheochromocytomas, SN serum levels w ere elevated up to 45-fold. Patients suffering from neuroblastomas, insulin omas, pituitary adenomas including acromegaly, and solid nonendocrine tumor s had concentrations in the normal range. In human serum, SN-immunoreactivity was confined to the free peptide SN; ne ither larger intermediate-sized forms nor the precursor secretogranin II we re detected. An efficient removal of the small molecule SN from the serum b y the kidney explains why SN serum levels are lower when compared to chromo granin A, which is present as large molecule in serum.