HEMODYNAMIC-CHANGES INDUCED BY SHORT-TERM AND LONG-TERM SODIUM-CHLORIDE OR SODIUM-BICARBONATE INTAKE IN DEOXYCORTICOSTERONE-TREATED RATS

The contribution of chloride to the haemodynamic changes of salt-depen dent deoxycorticosterone (DOC) hypertension was studied in young Wista r rats subjected to dietary loading with sodium chloride (NaCl) or sod ium bicarbonate (NaHCO3). Mean arterial pressure (MAP), cardiac output , systemic resistance (TPR) and arteriolar rigidity (estimated from pu lse pressure/stroke volume ratio, PP/SV) were determined in conscious chronically cannulated rats. DOC-induced increase of MAP and TPR appea red earlier in NaCl-loaded than in NaHCO3-loaded rats. After 4-6 weeks of hypertensive treatment MAP, TPR and PP/SV ratio were higher in DOC -treated rats fed NaCl diet than in those fed NaHCO3 diet. In contrast , after a long-term hypertensive regimen (lasting for 7-9 weeks) there was no significant difference in either MAP or TPR between rats loade d with NaCl or NaHCO3. On the other hand, DOC hypertension induced by a long-term feeding of NaHCO3, diet was not associated with an increas e of arterial rigidity which was characteristic for DOC-NaCl hypertens ive rats. Thus, a sufficiently long selective dietary sodium loading i s capable to increase the systemic resistance but not to alter the art erial rigidity. This was also confirmed by a comparison of brood press ure-matched DOC hypertensive rats fed NaCl or NaHCO3 diets. These anim als did not differ in the degree of systemic resistance elevation but the arterial rigidity was increased only in NaCl-loaded rats.