Reciprocal Consomic Strains to Evaluate Y Chromosome Effects

We have previously demonstrated that the SHRSP Y chromosome contains a locus that contributes to hypertension in SHRSP/WKY F2 hybrids and that SHRSP exhibit an increased vulnerability to focal cerebral ischemia after permanent middle cerebral artery occlusion (MCAO). This increased vulnerability is inherited as a codominant trait, and a putative role for the Y chromosome has been suggested in F1 hybrids. The objective of this study was to investigate further the role of Y chromosome in blood pressure (BP) regulation and in the vulnerability to cerebral ischemia. We have constructed consomic strains by selectively replacing the Y chromosome from WKY rats with that of SHRSP, and vice versa, by using a marker-assisted breeding strategy. Permanent MCAO was carried out by electrocoagulation, with infarct volume expressed as a percentage of the ipsilateral hemisphere. Systolic blood pressure was measured by radiotelemetry during a baseline period of 5 weeks followed by a 3-week period of salt loading. We observed that the transfer of the Y chromosome from WKY onto SHRSP background significantly reduced systolic BP in consomic strains, SP.WKYGlaY(w) (n=6) versus SHRSP (n=6) (209.2+/-10.4 mm Hg versus 241.7+/-7.7 mm Hg, F=5.88, P=0.038) during the salt-loading period. In the reciprocal consomic strain, WKY.SPGlaY(s) (n=5), systolic BP was increased compared with WKY parental strain (n=6) (147.6+/-2.4 mm Hg versus 132.6+/-5.1 mm Hg, F=6.11, P=0.035) during baseline. Infarct volumes in consomic strains were not significantly different from their respective parental strain: WKY.SPGlaY(s) (n=7) versus WKY (n=7), 22.8+/-3.7% versus 22.2+/-8.0%, 95% CI=-12.7, 4.2, P=0.3; SP.WKYGlaY(w) (n=7) versus SHRSP (n=6), 37.7+/-4.4% versus 33.6+/-7.6%, 95% CI=-20.3, 12.1, P=0.5. We conclude that the SHRSP Y chromosome harbors a locus contributing to systolic BP, whereas no contribution to vulnerability to cerebral ischemia can be detected.