Lack of effect of tannic acid on sodium balance in Microtus pennsylvanicus

Abstract

Effect of tannic acid on sodium (Na+) balance of captive meadow voles (Microtus pennsylvanicus) was studied by measuring size of the zona glomerulosa of the adrenal gland, a reflection of Na+ status, in voles provided diets containing three levels of Na+ and either 0, 1.5, or 5% tannic acid at each level of Na+. Na+, but not tannic acid, had a significant effect on size of the zona glomerulosa. The zona glomerulosa hypertrophied significantly in voles on diets containing the two lowest levels of Na+. Both tannic acid and Na+ had significant effects on relative body mass, indicating a nutritional constraint. However, results of this study do not support the widely cited hypothesis that tannins, such as tannic acid, disrupt Na+ balance in herbivores.