Radioimmunoassay study of neurophysins in human plasma.

Using a homologous system we have developed a specific and sensitive radioimmunoassay for the measurement of one of the human neurophysins in unextracted human plasma. This neurophysin is specifically secreted in response to oestrogen and has therefore been referred to as human oestrogen-stimulated neurophysin (h-OeSN). The plasma concentration was 0.57 +/- 0.17 ng/ml (SD) in females and 0.88 +/- 0.76 ng/ml (SD) in males. This difference is not significant. In women on oral contraceptives, plasma h-OeSN was 2.0 +/- 1.1 ng/ml. During pregnancy h-OeSN increased progressively to 3.7 +/- 2.9 ng/ml at the end of the first trimester, and 5.2 +/- 2.8 ng/ml at term. Plasma h-OeSN concentrations increased rapidly and markedly in men treated with ethinyl-oestradiol. We have also demonstrated the presence of h-OeSN in amniotic and cerebrospinal fluids. A second human neurophysin, which is stimulated by nicotine but not by oestrogen, was also measured. This neurophysin was monitored by a heterologous system using antiserum raised against bovine neurophysin II (b-NII), and b-NII as the standard and tracer.