Isolation and characterization of neurosecretory granules of the rat posterior pituitary gland

Summary Neurosecretory granules (NSG) of rat posterior pituitary glands were prepared by differential centrifugation techniques mainly according to the procedure as described by Barer, Heller and Lederis (1963). As revealed by electron microscopy, the recovery of neurophysin and the contents of enzymes, purified NSG were obtained in a pellet at 30 000 g/60 min (0.44 M sucrose). Eighteen h after injection of (³⁵S) cysteine into the supraoptic nucleus 60% of the recovered radioactivity in the neural lobe was found in the NSG, whereas 20% was found in the final supernatant (100 000 g/120 min). Sixteen days after injection the NSG and the final supernatant fraction contained fairly equal amount of (³⁵S) cysteine (approximately 40%). It is suggested that after a period of intragranular maturation neurophysin is extruded into an extragranular pool of neurosecretory material.With the use of conventional polyacrylamide-gel electrophoresis it was shown that the predominating proportion of radioactivity in the NSG after a hypothalamic injection of (³⁵S) cysteine was located within the neurophysin fraction A and in fraction B. Fraction B is suggested to be partly bound to the NSG membranes. When the NSG soluble and NSG insoluble proteins, obtained after lysis of NSG, were separated on polyacrylamide gels in the presence of sodium dodecylsulphate, the highly radioactive soluble protein was shown to consist of two components with average molecular weights of 12 300 and 14 600. Most of the proteins in the lysate were found in the NSG membranes, though less radioactive. A component with a mol.wt. of 37 000 was enriched in the membrane fraction. At longer times after isotope injection the high mol.wt. proteins, particularly those of the NSG membranes, contained increased amounts of radioactivity.Abbreviations NSG neurosecretory granule - NSM neurosecretory material - SON supraoptic nucleus The present investigation was supported by grants from Svenska Livförsäkringsbolags nämnd för medicinsk forskning from Svenska Sällskapet för Medicinsk forskning, from the Medical Faculty, University of Göteborg, and from the Swedish Medical Research Council (B 72-12X-2543-04A).We are indebted to Mrs. Marie-Louise Eskilsson, Mrs. Wally Holmberg and Mrs. Ulla Svedin for technical assistance, and to Miss Gull Grönstedt for careful secreterial work.