INDIVIDUAL NEUROPHYSIN CONCENTRATIONS IN THE PITUITARY AND CIRCULATION OF HUMANS

Abstract

Specific, homologous human neurophysin I and II radioimmunoassays were established and used to measure the individual, immunoreactive neurophysin concentrations in human plasma. Circulating levels of human neurophysin I in normal individuals were less than 1 ng/ml and neurophysin II levels were 1-2 ng/ml. During dehydration, there was a significant rise in plasma neurophysin I, with an increase in neurophysin II. Hemorrhage also was associated with a rise in plasma neurophysin I and II, but the percent increase was greater for I than II. In 2 subjects in whom nicotine inhalation caused a rise in plasma neurophysin I, there was no detectable increase in plasma neurophysin II. These stimuli which have been reported to release vasopressin from the posterior pituitary also are associated with the differential release of neurophysin I. Plasma neurophysin II levels could more clearly be shown to rise independently of plasma neurophysin I during events thought to be related to oxytocin release. Plasma neurophysin II levels were signficantly elevated in women taking oral contraceptives. Similarly, during pregnancy, there was a progressive rise in plasma neurophysin II concentration which was proportional to the period of gestation. Plasma neurophysin II concentrations in 7 of 15 nursing women rose significantly during suckling. There were no detectable change in plasma neurophysin I concentrations during any of these events. Plasma neurophysin I and II levels were both significantly elevated in 14 patients with chronic renal failure and rose over hemodialysis, suggesting that the kidney may be the major route of clearance of the neurophysins. In humans the independent release of neurophysin II was associated with stimuli thought to releae oxytocin, but neurophysin I showed only a differential release compared to neurophysin II in vasopressin stimulated events.