1. The cardiac mechanoreceptors, which in rats are mainly located in the left atrial wall, are reset in spontaneously hypertensive rats. The atrial pressure has to be almost twice as high in spontaneously hypertensive rats as in normotensive controls to produce similar receptor activations, as is apparent from previous studies.

2. The present study was performed to investigate whether this resetting is due to decreased distensibility of left atrial walls in the spontaneously hypertensive rats.

3. Static load-length relationships were investigated in vitro on left atrial strips, and pressure-volume relationships were studied on isolated left atria from spontaneously hypertensive and normotensive Wistar-Kyoto rats.

4. The force per cross-sectional area exerted during a relative length increase of 80% was significantly greater in spontaneously hypertensive rats. The dynamic but not the static distensibility was significantly lower in these animals.

5. The decreased dynamic distensibility of left atrial walls in spontaneously hypertensive rats can at least partly explain the resetting of atrial receptor function.

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