Left ventricular weight but not blood pressure is associated with sex chromosomes in Lyon rats

Objective To investigate, by studying reciprocal back-crosses to Lyon hypertensive (LH) rats, the involvement of sex chromosome loci in high blood pressure and heart weight in LH rats. Methods Reciprocal F-1 and F'(1) generation male rats obtained from male LH x female Lyon normotensive (LN) and male LN x female LH crosses respectively male back-cross rats obtained from male LH x female F-1 or F'(1) and from male F-1 or F'(1) x female LH crosses, and parental LH and LN male rats were studied at 29-31 weeks of age, Systolic, diastolic, mean and pulse pressures were measured beat to beat in unrestrained rats for 1 h. In addition, relative left and right ventricular weights were measured. Results The average blood pressures did not differ between F-1 and F'(1) rats or between the four populations of back-cross rats, On the contrary, the relative left ventricular weight was higher in F'(1) than in F-1 rats. As a role for loci on the Y chromosome could be discarded by comparison of the two populations of back-cross mts, which differ only in the origin of their Y chromosome, this increase in the relative left ventricular weight of F'(1) rats was consistent with an effect of a locus on the LH X chromosome. This was supported by findings in the back-cross populations, those populations in which 100% of the rats carried an LH X chromosome having a significantly higher left ventricular weight than those in which only 50% of the rats carried such a chromosome. The estimate of the genetic determination was higher for left ventricular weight (41%) than for mean arterial pressure (19%). Although these two parameters were associated in the back-cross population, the origin of the X chromosome had no influence on this association. Conclusions These findings indicate that, against the genetic background provided by the cross studied and at the age studied, the sex chromosomes of LH and LN rats do not contain loci at which alleles differentially influence blood pressure. They do, however, suggest that relative left ventricular weight in this model has a specific genetic determination, partly contributed by a locus on the X chromosome.