Release of vasopressin and oxytocin from isolated pituitary glands of adult and new‐born rats

Abstract

SUMMARY1. Pituitary glands of adult rats of both sexes, of lactating female and of new-born rats, incubated in a Locke solution, release both oxytocin and vasopressin. The amount of hormones released, during a measured period of incubation, is related to the actual hormone content of the gland.2. Increasing the concentration of KCI in the incubation medium, with CaO12 present and in concentration of at least 2-2 mm, produces an enhanced release of both hormones from pituitary glands of adults, but does not affect the release of hormones from glands of new-born animals.3. Addition of ouabain to the incubation medium produces a marked increase of the release of the hormones from glands of both adult and newborn rats. This is accompanied by an extrusion of K ion and an influx of Na ion. The effect of ouabain on the hormone release and the shift of ions can be reversed by subsequent addition of adenosine triphosphate.4. The increased release of hormones produced by ouabain, in glands from new-born rats, is unaffected by the presence or absence of CaCl2. In adults, however, the effect of ouabain, though present, is reduced in the absence of CaCl2.5. It is suggested that in glands from adult animals, the hormones must be freed from their attachment on the protein-carrier, neurophysin and that this can be achieved by the entry of calcium ion into the cell.

The Oxytocin Release and the Compound Action Potential Evoked by Electrical Stimulation on the Isolated Neurohypophysis of the Rat

“…In the adrenal medulla, the direct cause of depolarization of the chromaffin cell is not the propagated impulse but acetylcholine (Ach) released from the secretory nerve terminal (DOUGLAS et al, 1967). But it was confirmed that the neurohypophysial hormone could not be released by Ach applied to the isolated pituitary gland (DOUGLAS and POISNER, 1964;DICKER, 1966;DANIEL and LEDERIS, 1967). Therefore, it is likely that the change in permeability to Ca++ at the terminal of neurosecretory fiber in the neurohypophysis is caused by the arrival of the impulse itself.…”

Release of neurophypophysial hormones in vitro

“…However, membrane depolarization in the nerve terminals, by means of increased concentrations of potassium and calcium in the incubation medium, causes a pronounced release of vasopressin and oxytocin from isolated neural lobes (Douglas, 1963; Lederis, 1963;Douglas & Poisner 1964a; Dicker, 1966). The role of acetylcholine in the depolarization of the neural lobe nerve terminals is not known.…”

Stimulus-Secretion Coupling on the Oxytocin Release From the Isolated Posterior Pituitary Lobe

“…Although someinformation on the release of vasopressin from the isolated pituitary gland has been submitted (DOUGLAS and POISNER,1964a,b;DOUGLAS and ISHIDA,1965;ISHIDA,1967),little has been written on the release of oxytocin.Of course,plenty of studies have been carried out on the neural control of oxytocin secretion or the action of oxytocin on the uterine muscle (see"oxytocin"Ed.by CALDEYRO-BARCIA and HELLER,1961),but the onlyinformation concerning the release of oxytocin at the nerve terminal was submitted by DICKER(1966),describing that external Ca++is necessary for the release of oxytocin.…”