Release of Vasopressin and Oxytocin from Isolated Pituitary Glands of Adult and New-born Rats

1. 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 KCl in the incubation medium, with CaCl(2) 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 new-born 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 CaCl(2). In adults, however, the effect of ouabain, though present, is reduced in the absence of CaCl(2).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 subsequent secretion of the ;freed' hormones appears to be accompanied by a shift of ions across the cell membrane.6. In glands from neonates up to 3 weeks old, the absence of neurophysin, or its poor capacity for binding the hormones, explains the inability of calcium to operate in the same way as in the glands of adults. There is evidence suggesting that the secretion of the neurohypophysial hormones in the new-born animal consists mainly of their diffusion from the cells, without previous elution of the hormones as in adults.