The action and fate of injected posterior pituitary extracts in the decapitated cat

The fate of oxytocin in male and female rats

A method for quantitative extraction of oxytocin from blood is described. The disappearance of injected oxytocin from the circulation in rats was shown to depend upon its uptake in the kidneys and in organs of the splanchnic vascular area. In lactating rats there was uptake by an additional organ or tissue, probably the mammary gland. In animals without kidneys or lactating mammary glands and with no circulation in the splanchnic area oxytocin was distributed into a volume greater than the extracellular fluid volume, and after equilibration the concentration in plasma did not change significantly. During severe haemorrhage increased amounts of antidiuretic activity were detected in blood when there was no significant increase in oxytocic activity.

The inhibitory effect of the cerebellar fastigial stimulation on ADH secretion

1. Both cardiovascular and antidiuretic hormone (ADH) responses to some neural inputs were examined in paralysed anaesthetized cats.2. Carotid occlusion elicited cardiovascular responses and increased ADH secretion. When the electrical stimulation of discrete loci of the cerebellar fastigial nucleus (fastigial pressor area) was superimposed on carotid occlusion, cardiovascular responses were further facilitated, while ADH secretion was inhibited.3. The fastigial stimulation alone elicited facilitory cardiovascular responses composed of hypertension and tachycardia, and the fastigial pressor response (FPR), but did not evoke any consistent ADH response.4. These facts indicate that cerebellar modulation of ADH secretion occurs not directly via the hypothalamo-hypophysial system but through the lower brain stem to which both carotid sinus nerves and outflows from the fastigial pressor area project.5. We conclude that the fastigial pressor area is specific for not only cardiovascular and other autonomic responses but pituitary hormonal response.

The metabolism of exogenous and endogenous antidiuretic hormone in the kidney and liver in vivo

Negligible antidiuretic activity (less than 0.17 mU./g.) was found in extracts of the kidneys either of unanaesthetized adult rats in normal water balance or of rats in whose blood a rise of the level of endogenous antidiuretic hormone had been induced by ether anaesthesia. Extracts of the livers of unanaesthetized rats had negligible antidiuretic activity (less than 0.06 mU./g.), but liver extracts from rats anaesthetized with ether showed antidiuretic effects equivalent to 0.74+/-0.24 mU. Pitressin/g. liver. When Pitressin was injected intravenously into unanaesthetized rats, small amounts of antidiuretic activity were occasionally found in the livers and the kidneys of animals killed up to 3 min. after the injection but none in animals killed later. Some 3% of the antidiuretic activity of an injected dose of Pitressin was found in the urine and the "dead space" of the kidneys in rats decapitated 3 min. after the intravenous injection. When Pitressin was added to rat kidney homogenate and the mixture was incubated at 38 degrees , only 0.75% of the initial antidiuretic activity was recovered after 30 min. and less than 0.40% after 60 min. Experiments with "glomerular" and "tubular" fractions of rat kidney indicated that the inactivation was essentially due to tubular tissue. It is suggested that, in the rat, the kidneys and perhaps the liver are not only sites of clearance of the antidiuretic hormone but also sites of irreversible inactivation.

The synergistic action of the anterior and posterior pituitary hormones and their possible relation to eclampsia

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