THE PHYSIOLOGY OF NEUROPHYSIN SECRETION

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The aim of this grant has been to understand the role of neurophysins (the intraneuronal carrier proteins of vasopressin and oxytocin) in physiology and disease. We isolated two neurophysins from human pituitary, developed specific radioimmunoassays for each, and demonstrated each neurophysin was independently secreted. Assays for vasopressin and oxytocin were developed to document parallel secretion of hormone and neurophysin. Amino acid sequence of neurophysins proved that the vasopressin-neurophysins and the oxytocin-neurophysins in all species shared common sequence. Current thinking is that neurophysins are part of a common precursor from which are formed a hormone specific neurophysin and one hormone. With the assays which we have developed and with standard techniques of protein chemistry we can identify precursors of neurophysin in human and rat pituitary. We will now isolate sufficient precursor neurophysin from human pituitary to characterize the protein, to study its conversion to neurophysin and hormone, and to develop a radioimmunoassay for the precursor. In the human, precursors may serve as cancer markers and as evidence of pathologic secretion of hormone. In the rat, precursors can be used to identify rates of synthesis, transport and release of hormone. Content of precursor in the rat hypothalamus and pituitary will be measured in states of known hypersecretion of oxytocin and vasopressin to identify factors which control neurohypophyseal function. We will also study the "depletion/repletion" phenomenon whereby the rat attempts to maintain a constant store of hormone in the posterior pituitary in spite of increased or decreased release of hormone. We will measure the content of neurophysin, vasopressin and oxytocin in the pituitary to document depletion and repletion. We will infuse the products of synthesis (vasopressin, oxytocin and neurophysin) and neurotransmitters into the hypothalamus where the hormones are synthesized and measure the effect of the infusion on the depletion/repletion phenomenon to better understand the factors which turn on and off neurohypophyseal hormone biosynthesis. The information will help to understand the lack of secretion or the oversecretion of vasopressin (and oxytocin) in human disease.