Water Distribution Abnormalities in Hypothyroid Dogs Due to Acid-Base Disturbances 1

Abstract

Previous work by Dörr et al. (1) in this laboratory has shown that a hypertonic NaHCO₃ infusion increased extracellular water (ECW), measured as the rapidly equilibrating sucrose space, by 25% in hypothyroid dogs and only by 17% in euthyroid dogs. He suggested that this difference could be caused by an accumulation of mucopolysaccharides in the extracellular space of hypothyroids.

Substantially increased amounts of the mucopolysaccharide, hyaluronic acid, have been found (2) in the extracellular space of humans and animals with myxedema (the chronic form of hypothyroidism). This material has been localized in the ground substance of connective tissues. It has been demonstrated (3) that its polyelectrolyte characteristics make hyaluronic acid a very influential substance in determining water and electrolyte distribution in the body. Engel (4), Engel et al. (5) and Joseph et al. (6) studied the ion and water binding characteristics of the ground substance of connective tissues, and showed that under hormonal influences the macromolecules comprising the tissue would depolymerize. Their work demonstrated that ion and water shifts between the various body fluids occurred as a result of this change in the physicochemical state of the ground substance.

It is the hypothesis of this paper that the physicochemical state of the connective tissue ground substance is altered by changes in the hydrogen ion concentration of its environment (the interstitial fluid), and that these changes of state are particularly significant in the hypothyroid. Since a base infusion increased the extracellular and interstitial space in the hypothyroid as compared to the euthyroid, an acid infusion should yield comparable changes in the opposite direction. In the present study, a series of experiments was performed to measure the changes in water and electrolyte distribution in euthyroid and hypothyroid dogs as a result of an infusion of HCl.