Renal excretion and saline intake during post-stress immobilization period in rats

An experiment in which the rats access either to 0.5% or 1.5% saline was designed in order to further characterise the relationship between sodium intake and renal excretion after acute immobilization stress. A saline solution for 3 days was provided to the rats previous to the experimental day. On that day, after finishing acute immobilization stress, all variables under observation were measured every 6 h for 24 h. These periods were denominated as follows: T1 (12.00 to 18.00 h), T2 (18.00 to 24.00 h), T3 (24.00 to 06.00 h) and T4 (06.00 to 12.00 h). Acute immobilization stress reduced sodium renal excretion in both T1 and T2. Sodium intake in acute immobilization stress rats was lower than in control rats during all observed periods, while the urine volume was only reduced in the stressed animals in T1. These results were similar in both saline solution concentrations. A good correlation was observed between sodium intake and sodium excretion in control rats having access to either 0.5% or 1.5% saline as well as in stressed rats having access to 0.5% saline, this correlation was not observed in stressed rats with 1.5% saline. This suggests that stress impaired the renal capability of rats to handle high sodium but not a slight sodium overload. The inability of the kidney to excrete sodium may be critical to reduce sodium intake after acute immobilization stress.