BODY-FLUID ALTERATIONS AND ORGAN HYPERTROPHY IN AGE-DEPENDENT SALT HYPERTENSION OF DAHL RATS

The relationship between possible alterations in the volume or distrib ution of extracellular fluid and the development of salt hypertension was studied in inbred salt-sensitive (SS/Jr) and salt-resistant (SR/Jr ) Dahl rats. Blood pressure, cardiac and renal hypertrophy as well as body fluid volumes were determined in young and adult SS/Jr and SR/Jr rats of both sexes that were subjected to low, normal or high salt int ake for various periods of time. Salt hypertension in young salt-sensi tive rats fed a 4 % NaCl diet was not accompanied by any substantial i ntravascular or interstitial expansion as compared to salt-resistant r ats that remained normotensive. There was no sex difference in the res ponse of blood pressure or body fluids to high salt intake. Major expa nsion of plasma and blood volume, which was elicited by 8 % NaCl diet feeding from prepuberty, was not accompanied by a further blood pressu re rise (compared to salt hypertensive SS/Jr rats fed 4 % NaCl diet). In conclusions, salt hypertension can occur in Dahl salt-sensitive rat s without major salt and water retention. The degree of intravascular expansion is not directly related to blood pressure levels in salt-loa ded Dahl rats. A high salt intake seems to exert its hypertensive effe cts in Dahl rats preferentially by influencing the balance of vasocons trictor and vasodilator systems rather than by increasing the haemodyn amically active intravascular volume.