CHRONIC IMMOBILIZATION STRESS REDUCES SODIUM-INTAKE AND RENAL EXCRETION IN RATS

The influence of chronic exposure to immobilization (IMO) on sodium ap petite as well as sodium and potassium renal excretion in adult male W istar rats was studied. The animals were individually housed and all v ariables under observation were measured in metabolic cages the first, seventh, and thirteenth days once the experiment had started. Half of the rats had access to water, and the remainder of the rats had acces s to both water and saline solution (1.5% NaCl). IMO reduced the intak e of saline solution. Renal water, sodium, and potassium excretion in those IMO rats having access to saline were lower than in control rats . The effects of IMO were very similar during all observation days; th erefore no evidence of adaptation to repented stress was found. The pr esent data indicate the following: (i) IMO stress reduced sodium appet ite, probably as a secondary effect to the deficit in sodium renal exc retion; (ii) IMO caused antidiuresis and antikaliuresis, only in those rats taking saline solution; (iii) no adaptation to repeated IMO stre ss was found in any of the tested variables. The reduction of sodium a ppetite observed in stressed rats might be a homeostatic mechanism to maintain sodium balance after impairment of renal sodium excretion cau sed by stress. (C) 1997 Elsevier Science Inc.