Hypertension-Prone and -Resistant Dahl Rats

The effect of high salt intake on rascular and renomedullary prostaglandin (PG) synthesis was compared in Sprague-Dawley and salt-sensitive (S) and -resistant (R) Dahl rats. Animals were given a diet containing either 0.6% or 8% NaCI starting at 5 weeks of age, and were sacrificed 6 weeks later. Systolic blood pressure of S rats increased to 220 ± 7 mm Hg but was unaffected in R and Sprague-Dawley rats. Prostaglandin synthesis was studied in aortic rings and renomedullary mlcrosomes using C-arachidonate as substrate. [*H]PGE, degradation was measured in the renocortical cytosol. In Sprague-Dawley and R rats, aortic PGIt synthesis was not affected by high salt intake, while a significant increase compared to animals on 0.6% NaCI (from 608 ± 84 to 992 ± 108 pmoles/60 min, p < 0.05) was noted in S rats. Enhancement of PGI| synthesis in S rats may be secondary to the hypertension. Salt-loading consistently stimulated renomedullary PGE, synthesis in all three animal groups. S rats, however, had the lowest PG synthesis in renal medullas compared to Sprague-Dawley and R rats when placed on either diet. Thus, even after 6 weeks on high salt, S rats did not reach the levels of PGE, synthesis seen in R or Sprague-Dawley rats on regular diet. The activity of cortical 15-hydroxyprostaglandin dehydrogenase was increased by salt-loading in S and Sprague-Dawley, but not in R rats. R rats had lower dehydrogenase activity than the other two groups when placed on either diet. The observed differences in PG synthesis and catabolism will tend to maintain the net output of renal PGs highest in R and lowest in S rats. These differences correlate with the reported differences in renal papillary flow between these two rat strains and may be relevant to their susceptibility or resistance to hypertension in response to salt. (Hypertension 3: 219-224, 1981) ;