Polyamines in nerve terminals and secretory granules isolated from neurohypophyses

In isolated nerve terminals from ox neurohypophyses the following concentrations of polyamines [pmol (microgram protein)-1 (mean +/- SEM)] were found: spermine: 2.07 +/- 0.14 (n = 3), spermidine: 0.22 +/- 0.01 (n = 4), putrescine: 0.20 +/- 0.01 (n = 4). In secretory granules isolated from the same tissue, the concentrations were: spermine: 0.57 +/- 0.02 (n = 3), spermidine: 0.07 +/- 0.04 (n = 3), putrescine: 0.13 +/- 0.04 (n = 3). After incubation of isolated nerve terminals with the polyamines, they were taken up as a function of time and concentration, approaching saturation at high concentrations. The kinetic parameters of their synthesizing enzyme, ornithine decarboxylase, in ox neurohypophyseal nerve terminals (apparent Km 0.75 mM and Vmax 22.5 pmol mg protein-1 h-1) were comparable to those previously found in cerebral cortex of rats. When isolated, hemilobes from rat neurohypophyses were incubated in a medium which contained spermidine (5 mM), and were stimulated by 56 mM K+, release of vasopressin was smaller than in control experiments. However, after removal of spermidine and after restimulation, 50 min after initial stimulation, the release was significantly elevated. It is suggested that polyamines may take part in modulation of vasopressin release.