Further chromosomal mapping of a blood pressure QTL in Dahl rats on chromosome 2 using congenic strains

Both linkage and use of congenic strains have shown that a region on rat chromosome 2 (Chr 2) of Dahl salt-sensitive rats (S) contained a quantitative trait locus (QTL) for blood pressure (BP). A congenic strain was made by replacing a segment of the S rat by the homologous region of the Milan normotensive (MNS) rat. Since the region was roughly 80 cM in size, a further reduction is required toward the final identification of the QTL. Currently, three congenic substrains were made by replacing smaller sections within the 80 cM. Each strain contains a specific region of MNS in the S genetic background. Two of the three congenic strains shared a segment in common, and both showed a BP-lowering effect. One of the three congenic strains carried a unique segment and had the same BP as S. Deducing the fragment shared in the two substrains having an effect, the BP QTL has to be present in a region of roughly 15 cM. In contrast to BP, heart rates of all the congenic rats were the same as that of the S rat. Thus BP and the heart rate are under the control of independent genetic determinants.