Ampholyte displacement and high pressure liquid chromatographic separation of the estrogen-responsive neurophysin from human plasma

Oestradiol acutely stimulates exocytosis of oxytocin and vasopressin from dendrites and somata of hypothalamic magnocellular neurons

Oestrogen has many direct or indirect actions upon the magnocellular system of the hypothalamus. We have examined the possibility of acute actions of oestrogen upon the magnocellular system by stimulating slices of supraoptic nucleus in vitro with various concentrations of oestrogen, for varying lengths of time, and assessing the intrahypothalamic release of oxytocin and vasopressin under these conditions. Slices were stimulated in the presence of tannic acid, which precipitates extracellular protein and thereby stabilizes exocytosed neurosecretory granule cores. Stimulation for 5 or 20 min of slices of hypothalamus containing the supraoptic nuclei with 2.66 nM-26.6 microM 17 beta-oestradiol benzoate caused the exocytosis of granules from both dendrites and cell bodies of the magnocellular neurons; exocytosis from the dendrites predominated. Granules of both oxytocin- and vasopressin-producing cells were exocytosed to a similar extent. The incidence of exocytosis of both hormones after stimulation by oestrogen was significantly higher than after exposure either to physiological saline or to 17 alpha-oestradiol, but significantly lower than after stimulation by 56 mM potassium. The various doses of steroid and durations of stimulation all resulted in similar amounts of captured exocytosis. Furthermore, the oestradiol-induced release was not inhibited by removal of extracellular calcium, whereas the potassium-stimulated release was abolished. Exposure for 20 min to either testosterone or progesterone did not induce intranuclear release of significant numbers of neurosecretory granules from the magnocellular neurons. In contrast to its effect on the hypothalamus, 26.6 microM oestradiol for either 20 min or 5 min did not induce exocytosis of neurosecretory granules from the posterior pituitary. We conclude that oestrogen can exert acute non-genomic actions on the magnocellular neurons to promote intrahypothalamic release of oxytocin and vasopressin. This effect is probably direct on the magnocellular neurons as it is not dependent on external calcium. Such actions may be important in the development of the functional and morphological plasticity of the magnocellular system that occurs in parturition and lactation.

Ovarian oxytocin and neurophysin concentrations in the cynomolgus monkey (Macaca fascicularis)

The neurohypophysial hormone oxytocin has previously been found in the ovaries of several animal species. In ruminants ovarian oxytocin is postulated to have a luteolytic function, because of its high concentrations in the corpus luteum. In primates the role of ovarian oxytocin is not known. In the present study we measured the immunoreactive oxytocin and oxytocin-neurophysin content in paired ovaries removed from cynomolgus monkeys (Macaca fascicularis) during the late luteal phase of the cycle (Days 12-14 of the luteal phase or Days 26-28 of a menstrual cycle). Each animal was pulsed with synthetic gonadotropin-releasing hormone to maintain normal menstrual cyclicity. The concentration of oxytocin and its neurophysin during the late luteal phase was greater in the non-corpus luteum than corpus luteum-bearing ovary. By high pressure liquid chromatography and bioassay the oxytocin in both the corpus luteal and non-corpus luteal ovaries was similar to synthetic and posterior pituitary oxytocin. The finding of high concentrations of immunoreactive oxytocin in the non-corpus luteum-bearing ovary suggests that the function of ovarian oxytocin in primates may not be confined specifically to the corpus luteum.

Oxytocin and vasopressin are present in human and rat pancreas

Immunoreactive oxytocin and vasopressin were found in human and rat pancreatic extracts. The pancreatic oxytocin and vasopressin eluted on Sephadex G-75 gel filtration chromatography and on reverse phase high pressure liquid chromatography in the same positions as their respective reference preparations. The immunoreactive oxytocin was biologically active in the rat milk ejection assay. The presence of oxytocin and vasopressin in human and rat pancreatic extracts suggests the possibility of local synthesis of both hormones. The neurohypophysial hormones are known to be endocrine mediators of insulin and glucagon release. The finding of oxytocin and vasopressin in the pancreas raises the possibility, although yet unproven, of local synthesis and perhaps a paracrine function for the neurohypophysial peptides upon pancreatic hormone release or for a local function upon the liver.