Effect of Lowered CSF Sodium Concentration on the Central Control of Fluid Balance

The results indicate that, instead of osmolality, the ionic composition of CSF is important for ADH release, and support the concept of a Na+ sensitive receptor system near the third ventricle.

Abstract

Abstract Isotonic and hypertonic non‐electrolyte solutions were slowly infused into the cerebral ventricular system of conscious goats in normal water balance. Infusions of all the isotonic solutions induced water diuresis. When the infusions were made into the anterior part of the lateral ventricle, the response was more delayed than when the solutions were infused into the third ventricle. Also, hypertonic (0.45 M or 0.6 M) solutions of d‐glucose, d‐fructose, glycerol, and sucrose turned renal CH 2 O positive. Hypertonic urea, instead, gave inconsistent responses. The observed increase in renal CH 2 O obviously resulted from an inhibition of the normal release of ADH. Firstly, there was no increase in renal C 0 sm; and secondly, intravenous injection of ADH interrupted this water diuresis. No obvious changes occured in renal electrolyte excretion, blood pressure, and heart rate during infusions. After infusions, when CH 2 O returned to the preinfusion level, there was sometimes a slight increase in sodium excretion and blood pressure. Infusions of isotonic saccharides in physiologic saline did not induce water diuresis under infusions, but after infusions there was (in 4 out of 6 cases) some increase in urine flow and CH 2 O could become positive for 10 to 20 min. These results indicate that, instead of osmolality, the ionic composition of CSF is important for ADH release, and support the concept of a Na + sensitive receptor system near the third ventricle.