Sodium and Potassium Effects on Adrenal-Gland Indices of Mineral Balance in Meadow Voles

We compared sodium and potassium content of plants with the dietary levels of low sodium and high potassium that stimulate hypertrophy of the zona glomerulosa of the adrenal gland of Microtus pennsylvanicus. The zona glomerulosa typically enlarges in animals subjected to severe sodium shortage or potassium overload. Among voles maintained on several low sodium diets, the relative size of the zona glomerulosa was elevated significantly only on the lowest sodium diet (0.00043 mol/kg or 10 ppm). This level of sodium is extremely low for plant sodium contents in nature. Dietary potassium levels ≥0.614 mol/kg or 24,000 ppm induced significant increases in size of zona glomerulosa; few plant species we analyzed had potassium levels below these early in the growing season. From our results, we suggest that potassium excess may play a more central role than sodium deficiency in the seasonal mineral-balance dynamics of this herbivore species.