The Release in Vitro of Vasopressin Unaccompanied by the Axoplasmic Enzymes: Lactic Acid Dehydrogenase and Adenylate Kinase

Abstract

Lactic acid dehydrogenase (LDH) and adenylate kinase were shown by differential centrifugation to be mainly associated with the supernatant fraction of ox neurohypophyses. In vitro release of vasopressor activity, LDH and adenylate kinase from groups of rat neural hemilobes or slices of ox neurohypophyses was studied at rest and after stimulation with a high potassium concentration or after electrical stimulation. Although release of vasopressor activity increased considerably on stimulation, no significant change in the release of LDH or adenylate kinase could be detected. The findings are discussed in relation to the different hypotheses for the mechanism of release of vasopressin.

Fusion of neurohypophyseal membranes in vitro

“…Also, treatment of isolated neurohypophyses with ionophores, which increase intracellular, free Ca 2+ concentration by increasing transmembrane transport, can induce secretion [5,6]. Both ultrastructural [7] and biochemical [8,9] studies suggest that secretion in the neurohypophysis as in various other endocrine systems [10], occurs by exocytosis. However, the events that are triggered by 46 Ca 2+ leading to exocytosis are not resolved.…”

Stimulation-dependent uptake of an extracellular marker to subcellular fractions of isolated neurohypophysial tissue

“…Some essential facts are known about the mechanism by which the neurohypophysial hormones Vasopressin and Oxytocin are released. It has been reported that on Stimulation of isolated rat neurohypophyses, vesicles containing Oxytocin and the binding protein (neurophysin) release their contents to the medium in a roughly stoichiometric way 4 , whereas axoplasma enzyme markers are not released 5 . These facts support the hypothesis that release occurs by exocytosis.…”