Isolation, Assay, and Secretion of Individual

acetone-dried human posterior pituitaries and separated into two major neurophysin peptides by ion exchange chromatography and into four major peptides by pre-parative disk gel electrophoresis. Antisera raised in rabbits distinguished only two specific antigenic sites on the isolated neurophysin peptides. Individual sensi-tive and specific radioimmunoassays for two human neurophysins were developed. These assays were used to measure each neurophysin in unextracted human plasma. The two neurophysins are secreted indepen-dently in man. One assay measures a neurophysin that is specifically secreted in response to estrogen admin-istration, estrogen-stimulated neurophysin (ESN). The other assay measures a neurophysin that is specifically secreted in response to cigarette smoking, nicotine-stimulated neurophysin (NSN). The mean ESN is 1.1 ng/ml±0.7 SD in women and 1.0 ng/ml±0.7 SD in men. The mean NSN is 0.9 ng/ml±0.2 SD in women and 0.6 ng/ml±0.3 SD in men. It is proposed that these may prove to be a specific human "oxytocin-neurophysin, " ESN, and a human "vasopressin-neuro-physin, " NSN