Effect of Diminishing Doses of Post-Pituitary Extract on Urinary Excretion of Water and Chlorides

Previous work has indicated that, when the dose of injected post-pituitary extract is progressively reduced, the excretion rates of water and chlorides were changed independently of one another. 1 The present experiments were designed to extend these observations by following the change in urinary excretion over a wide range of extract dosage. Thus the dose of extract was varied from 3000 milliunits per 100 g of body weight down to 2.5 milliunits. White rats were employed, weighing about 200 g. Each animal was used but once to prevent any possible complication due to sensitization or tolerance to the pituitary extract. The animals were given intra-peritoneal injections of 10 cc of 0.2% sodium chloride solution per 100 g of body weight with which had been mixed the calculated amount of pituitary extract.∗ They were then placed in metabolism cages for 6 hours, and the urine collected and analyzed for chlorides. 1

The data are presented in Table I. These show that as the dosage of the extract was progressively decreased, the excretion of water gradually increased while that of the chlorides steadily diminished. The water excretion approached the normal level much more rapidly than the chloride excretion, however: and, when the dosage of the extract was reduced to 5 milliunits, it was observed that the urine excretion was now inhibited to the extent of only 11%, while the chloride output was still 280% above the normal level. When the amount of pituitary extract was reduced still further (e.g., to 2.5 milliunits) no significant change from the control levels could be observed. This dosage, therefore, was concluded to be sub-minimal, at least in respect to the chloride and water changes.