BLOOD-PRESSURE AND SURVIVAL OF A CHROMOSOME-7 CONGENIC STRAIN BRED FROM DAHL RATS

11 beta-hydroxylase (Cyp11b1) mutations were previously linked to alte red steroid biosynthesis and blood pressure in Dahl salt-resistant (R) and Dahl salt-sensitive (S) rats. In the present work, interval mappi ng identified a putative blood pressure quantitative trait locus (QTL) near Cyp11b1 in an F-1(SxR)xS population (LOD = 2.0). Congenic rats ( designated S.R-Cyp11b) were constructed by introgressing the R-rat Cyp 11b1 allele into the S strain. S.R-Cyp11b rats had significantly lower blood pressure and heart weight compared with S rats, proving the exi stence of a blood pressure QTL on Chromosome (Chr) 7 despite the fact that QTL linkage analysis of blued pressure never achieved stringent s tatistical criteria for significance. To test the effects of the intro gressed region on blood pressure and survival, S.R.-Cyp11b and S rats were maintained on a 4% NaCl diet until they died or became moribund. Analysis of variance (ANOVA) indicated significant strain differences in blood pressure and days survived (P < 0.0001 for both) as well as g ender differences in days survived (P = 0.0003). Kaplan-Meier survival analysis also found significant strain (P < 0.0001) and gender (P = 0 .007) differences in days survived. However. when the effects of blood pressure were removed, significant strain differences in survival ess entially disappeared. This suggests that the increased survival of S.R -Cyp11b rats was largely due to their decreased blood pressure and thu s strongly corroborates the existence of a blood pressure QTL on Chr 7 near or at Cyp11b1.