Summary
Posterior pituitary glands from normal rats, and rats which had been deprived of water for varying periods, were examined by the freeze-fracture method. This technique reveals large areas of the nerve cell membrane. Images consistent with exocytosis as the mechanism of release of the neurohypophysial hormones were observed. These modifications were most numerous after the rat had been starved of water for 2 days.
In normal rats, the large number of neurosecretory granules within the nerve fibres caused a bulging of the nerve cell membrane. The “bulges” disappeared 2 days after removal of drinking water. Regions of the membrane displaying “bulges” were characterised by the absence of the typical membrane-associated particles.
It is postulated that the close proximity of the neurosecretory granules to the nerve cell membrane may result in rapid fusion of the neurosecretory granules on stimulation of the gland. The change in properties of the nerve cell membrane overlying the neurosecretory granules, as suggested by the loss of membrane-associated particles, may represent a change in the structure of the membrane to a form which is more favourable for fusion.
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This work was supported in part by a grant from the New Zealand Medical Research Council.
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Dempsey, G.P., Bullivant, S. & Watkins, W.B. Ultrastructure of the rat posterior pituitary gland and evidence of hormone release by exocytosis as revealed by freeze-fracturing. Z.Zellforsch 143, 465–484 (1973). https://doi.org/10.1007/BF00306766
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DOI: https://doi.org/10.1007/BF00306766