On the Influence of the Neurohypophyseal Principles on the Sodium Metabolism in the Axolotl (Amblystoma mexicanum)

Abstract

Summary. The active uptake of sodium from dilute solutions of sodium chloride by the axolotl has been studied with radio‐sodium. The mean rate of uptake was found to be 68.7 μequiv. per day. The daily excretion of starving animals was found to be somewhat higher, viz. 94.6 μequiv. Injection of Insipidin, a pressor preparation from the neurohypophysis, induces a net uptake of sodium and chlorine lasting for several days. Studies with radio‐sodium revealed that the net uptake is due to an increased active uptake (the increase amounting to 200% of the normal sodium uptake), whereas the excretion is not depressed. Indeed, an increase in the excretion lasting for several hours after the injection was always seen. The oxytocic principle, represented by the preparation Pitupartin, induces a rapid net loss of sodium and chlorine lasting for 2–5 days. This loss was found to be due to an increased excretion, whereas the active sodium uptake was practically unaffected, apart from a short increase in the rate of uptake immediately after the injection. The injection into the animals of hypertonic sodium chloride solution calls forth an increase in the active uptake as well as in the excretion of sodium. After a few hours, both uptake and excretion as a rule returned to the normal level. The mere introduction of the injection needle produced a quite similar reaction. This pricking effect is easily distinguished from the pressor principle reaction on account of the short duration of the former. The results are discussed and it is concluded that the transient increase both in excretion after Insipidin and in uptake after Pitupartin may be due to the pricking effect, so that the pressor principle may be assumed to act upon the active salt uptake only, whereas the oxytocic principle mainly (or only) increases the rate of the salt excretion.