Isolation and partial characterization of two human neurophysins: their use in the development of specific radioimmunoassays.

Two neurophysins (NPs) that are thought to be the primary protein forms produced with the hormones vasopressin (VP) and oxytocin (OT) were isolated from 5000 human pituitary glands. In sucrose gradient centrifugation of human neural lobes, each of these NPs had a distribution similar to that of either VP or OT. Such differential localization of 1 human NP (HNP) with VP and the other HNP with OT suggests an association of their biosynthesis, and it is on the basis of this association that 1 NP has been named VP-associated HNP (VP-HNP) and the other OT-associated HNP (OT-HNP). The purified proteins were complexed to bovine thyroglobulin in order to develop specific antisera. RIAs developed with these antisera are effective for each HNP in the range of 5-320 pg. Reference standards in both assays were corrected for protein content using amino acid analysis to obtain absolute protein concentration; this type of correction is recommended for all RIAs that measure proteins. The RIAs were used to measure the concentrations of HNPs in unextracted human plasma. In healthy, sitting, normally hydrated subjects of both sexes, VP-HNP and OT-HNP were, respectively, 73 +/- 5 and 382 +/- 30 pg/ml (mean +/- SEM; n = 20); there was no significant difference between values in males and females, provided the latter were not taking medication. Women on oral contraceptives had elevated (> 3 times normal) levels of OT-HNP but normal levels of VP-HNP. Eleven patients who had the syndrome of inappropriate secretion of antidiuretic hormone had elevated levels of VP-HNP but not necessarily of OT-HNP. Surgery was found to consistently increase plasma VP-HNP but not OT-HNP. In two of six subjects smoking caused a dramatic release of VP-HNP, as indexed by plasma levels which rose to more than 50 times the control values. One patient with lithium-induced nephrogenic diabetes insipidus had elevated plasma concentrations of both NPs. The sensitivity and specificity of the RIAs may make them useful clinically in certain pathological states.