Dynamic Response to Long‐Term Sodium Loading and Restriction

Abstract

Plasma sodium concentration is controlled within very narrow limits. During changes in sodium intake, plasma sodium concentration deviates minimally from its normal value. Sodium intake was increased from a normal to a high level (208 % of normal) for 5 days and then dropped to a low level (13% of normal) for subsequent 5 days in He et al's experimental study (Hypertension.38:321‐325, 2001). Plasma renin, aldosterone and sodium concentrations were measured. He et al. reported decreases in renin and aldosterone concentrations and a small increase in plasma sodium concentration during sodium loading. During the subsequent 5 days of sodium intake decrease, there was an increase in plasma renin and aldosterone concentrations and a small decrease in plasma sodium concentration. The mathematical model we developed was tested with He et al.'s experimental findings in our previous study. And it was shown that the model gave similar results to the experimental work. In this study, to analyze the response dynamics in detail, the rate of change (derivative) of plasma renin, aldosterone and sodium concentrations during sodium loading and restriction were calculated by using the same model. According to the model, the maximum value of the rate of change of plasma renin, aldosterone and sodium concentrations during sodium restriction is larger than during the sodium loading condition. The possible reason of this simulation result is that the absolute change in the sodium intake from a high level to a low level is larger than the change in the sodium intake from a normal to a high level during sodium loading in the model.