Other rats strains and selection lines

Much less research has been done in other strains. In a recent paper the baseline blood pressure and heart rate of six strains were compared (van den Brandt et al, 1999). The authors found clear differences in blood pressure, with, for instance, F344 rats having a significantly higher systolic and diastolic blood pressure than LEW rats. The same difference is also found for the baseline heart rate. Interestingly, whereas the heart rate show a clear circadian rhythm in the F344 rats, this seems absent in the LEW rats. A similar disturbance of circadian rhythm is also seen in BN rats, but not in WKY and DA rats.

As mentioned above, this disturbance in circadian rhythm in LEW and BN rats was also observed in HPA axis activity, and thus this seems to be a general phenomenon of both lines.

RHA/Verh and RLA/Verh do not show a clear difference in baseline heart rate (Roozendaal et al., 1992). However, when exposed to novelty, RLA/ Verh show a clear reduction in heart rate, whereas RHA/Verh do not (Roozendaal et al., 1992). This is particularly striking, since most strains show an increase in heart rate after exposure to novelty.

In a recent pilot study we have started to investigate the heart rate in APO-SUS and APO-UNSUS rats, and found that the baseline heart rate is significantly higher in APO-SUS rats compared to APO-UNSUS rats. This was seen most clearly during the daytime (when rats were resting), though the effect was also present during the active night period (unpublished data). Data with respect to blood pressure or stress responsiveness of either heart rate or blood pressure are not yet available.

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