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Institute of Neurobiology, University of Göteborg, Fack, S-400 33 Göteborg, Sweden
(Received 7 February 1975)
Brattleboro rats which have hereditary hypothalamic diabetes insipidus (DI) are unable to synthesize vasopressin, but produce oxytocin adequately (Valtin, 1967). Vasopressin and oxytocin are considered to be synthesized along with their respective 'carrier' polypeptide, neurophysin (see Sachs, 1970), and in accordance with this notion, DI rats have been shown to lack one neurophysin, suggested to be connected with vasopressin (Friesen & Astwood, 1967; Burford, Jones & Pickering, 1971).
The synthesis of vasopressin occurs according to the RNA coding principle for protein synthesis (see Sachs, 1970). In view of the fact that the amino acid sequence is known for hormones and neurophysin (see du Vigneaud, 1954–5; Walter, Schlesinger, Schwartz & Capra, 1971), DI rats provide a model system for investigating factors controlling the synthesis of these peptides.
In the present investigation the quantity of RNA in
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SUMMARY
The effect of salt-loading, thirst and water-loading on the axonal transport and turnover of neurohypophysial proteins in rats was investigated by measuring the radioactivity of the neural lobe proteins at various time intervals after injection of [35S]cysteine into the region of the supraoptic nucleus. Osmotic stimuli did not markedly affect the rate of transport of either the rapid or the slow phase of axonal transport of proteins. In dehydrated rats the increase of neurohypophysial radioactivity during short time intervals after isotope injection exceeded that in controls, demonstrating an increased axonal transport due to osmotic stimuli. The turnover of rapidly as well as slowly transported neurohypophysial proteins was increased after dehydration but was decreased in water-loaded rats. After water deprivation or salt-loading with 2% NaCl solution for 7 days the neural lobe neurophysin was reduced in amount by 80–90%, whereas during salt-loading with 1% NaCl solution a 20% reduction was observed on the 14th as well as the 30th day. As judged from the amount of radioactivity in posterior pituitary neurophysin in dehydrated rats it is suggested that newly synthesized rapidly transported neurophysin is rapidly released after its arrival in the neural lobe.
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SUMMARY
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.