EFFECT OF SUCKLING AND PARTURITION ON AXONAL TRANSPORT AND TURNOVER OF NEUROHYPOPHYSIAL PROTEINS OF THE RAT

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Abstract
The effect of suckling and parturition on axonal transport and turnover of neurohypophysial proteins was studied by determining the radioactivity in neural lobe proteins after injection of [35S]cysteine into the region of the supraoptic and paraventricular nuclei in rats. Evidence was obtained for a lag period of more than 1 h before newly synthesized material is ready for transport along the neurohypophysial tract. Neither suckling nor parturition induced any noticeable reduction in amount of neural lobe neurophysin. The axonal transport of newly synthesized neurophysin was increased after suckling and parturition. Gel electrophoresis showed the same pattern of radiolabelling of neurohypophysial proteins as in normal female rats. The turnover of neurohypophysial proteins was increased after prolonged suckling. Differences in mode of release of oxytocin- and vasopressin-neurosecretory material are discussed. It is suggested that the neurohypophysial pool of oxytocic neurosecretory products is homogeneous.