Identification of vasopressin-like peptides in the plasma of a patient with the syndrome of inappropriate secretion of antidiuretic hormone and an oat cell carcinoma.

In this study we have identified and characterized several vasopressin-like peptides in the plasma of a patient with the syndrome of inappropriate antidiuretic hormone secretion and oat cell carcinoma of the lung. Immunoreactive plasma vasopressin was measured after gel filtration (Sephadex G-25) or C-18 cartridge extraction using two different region-specific antisera: AS1 and AS2. Antiserum AS1 is more specifically directed towards the antigenic site of the hexapeptidic ring of arginine-vasopressin (AVP), whereas AS2 is more specifically directed towards the C-terminal region of AVP. Unexpectedly, the Sephadex G-25 gel filtration elution profile of the immunoreactive vasopressin was very heterogeneous, indicating the presence of several molecular species. After extraction of total AVP and AVP-like peptides of this plasma, an unusual AS1/AS2 ratio of immunoreactivity was observed, suggesting the presence of vasopressin-like peptides which differ from AVP in the C-terminus.