Evidence for primary genetic determination of heart rate regulation: chromosomal mapping of a genetic locus in the rat.

BACKGROUND

We investigated whether an accelerated heart rate (HR), observed in the stroke-prone spontaneously hypertensive rat (SHRSP(HD)), is a primary, genetically determined trait and whether it contributes to blood pressure (BP) regulation in this model of polygenic hypertension.

METHODS AND RESULTS

We measured BP and HR in SHRSP(HD) and normotensive Wistar-Kyoto rats (WKY), as well as in F2 hybrids bred from crossing the two strains, at baseline and after 12 days of dietary NaCl loading. Random marker genome screening and cosegregation analysis were performed on F2 hybrids derived from SHRSP(HD)/WKY-0(HD) (n=115) and SHRSP(HD)/WKY-1(HD) (n=139) crosses (WKY-0(HD) and WKY-1(HD) are two congenic WKY strains). HR in SHRSP(HD) was significantly higher than in WKY-0(HD) both at baseline (404+/-30 versus 375+/-46 bpm; P=.0034) and after NaCl (437+/-23 versus 364+/-40 bpm; P=10(-9)). BP in F2 hybrids showed no significant correlation with HR either at baseline or after NaCl loading. HR after NaCl loading but not at baseline was significantly linked in a recessive fashion to a locus on chromosome 3: in animals homozygous for the SHRSP(HD) allele, HR was 414+/-49 compared with 383+/-44 bpm in heterozygotes and WKY homozygotes (F(210,1)=19.7, P=1.4x10(-5), lod score=5.9). The putative BP-relevant gene at this locus, termed HR-SP1, showed no evidence of linkage to any of the BP parameters measured.

CONCLUSIONS

Our results demonstrate that a genetic locus on rat chromosome 3, HR-SP1, contributes directly to the regulation of HR in SHRSP(HD) but exhibits no effect on BP. Thus, in addition to its modulation by reflex-mediated neurohumoral mechanisms, HR is also under the direct influence of primary genetic factors.