Genetically defined risk of salt sensitivity in an intercross of Brown Norway and Dahl S rats

A genetic segregation analysis was performed to identify genes that cosegre gate with arterial blood pressure traits reflective of salt sensitivity. A population of 113 F2 male rats was derived from an intercross of inbred SS/ JrHsd/Mcw (Dahl salt-sensitive) and BN/SsN/Mcw (Brown Norway) rats. Rats we re maintained on an 8% salt diet from the age of 9 to 13 wk, and arterial p ressure was measured for 3 h daily during the 4th wk of high salt intake in unanesthetized rats using implanted arterial catheters. At the end of the 3rd day of high-salt pressure recordings, the arterial pressure response to salt depletion was determined 1.5 days following treatment with Lasix and a low-sodium (0.4%) diet. A genome-wide scan using 265 polymorphic simple s equence length polymorphism (SSLP) markers found that seven arterial pressu re phenotypes determined at different times and circumstances, and represen ting two distinct indexes of salt sensitivity, mapped to the same region of rat chromosome 18. The trait of salt sensitivity was strongly influenced b y the presence of SS alleles in this region of chromosome 18, and those rat s which were homozygote SS/SS exhibited a significantly greater reduction o f mean arterial pressure following sodium depletion (29 +/- 2 mmHg) than ho mozygote BN/BN (17 +/- 3 mmHg) or heterozygotic (22 +/- 2 mmHg) rats. This region of rat chromosome 18 corresponds to the long arm of human chromosome 5 and a region of human chromosome 18 that has been linked to hypertension in humans. Given the unlikely chance of these different blood pressure tra its mapping to the same region, we believe these data provide evidence that this region of rat chromosome 18 plays an important role in salt-induced h ypertension.