Water and electrolyte balance in normal and hypertrophied hearts.

Abstract

The condition of arteriosclerosis was simulated in male, Wistarstrain rats by sub-diaphragmal aortic constriction. Two days after constriction, a significant (P < 0.05) increase in cardiac mass had occurred. Significant changes in extracellular fluid volume and electrolyte content of the left ventricle, right ventricle and atrium were found much sooner than changes in cardiac mass and may thus play a role as instigating factors in the mechanism of cardiac hypertrophy. The extracellular fluid volume was measured by a radioactive isotope dilution method employing S35-sulphate. Significant increases in sulphate space and sodium content were found to occur in the left ventricle within 24 hours after aortic constriction. These increases became even more significant (P < 0.001) at 10 days, then both parameters decreased to within normal range between 2 and 3 weeks after aortic constriction. Close correlation (r = 0.915) was found between sulphate space and sodium content in both ventricles of hypertrophied hearts. Total water remained remarkably constant in the left ventricle but rose significantly in the right ventricle of hearts with the greatest degree of hypertrophy (over 66% increase). Potassium content remained unchanged in the left ventricle but dropped significantly in the right ventricle, as did total phosphate. The same parameters were measured in different regions of normal hearts of unoperated, 150 to 450 gram rats. It was found that sulphate space, total water, sodium content, intracellular potassium, etc. all reached maximal values in the 250 to 300 gram rats and then all (except sodium) decreased in larger rats. Because this weight group occurs at the steepest part of the normal growth curve, these changes in water and electrolyte values are thus associated with rapid normal growth as well as with the accelerated growth of cardiac hypertrophy. Possible reasons for the observed changes in water and electrolyte balance are discussed from the point of view of hormonal, metabolic, hemodynamic and physical changes.