Resetting of cardiac C-fiber endings in the spontaneously hypertensive rat.

The characteristics of 11 left atrial receptors in 9 adult male spontaneously hypertensive rats (SHR) were investigated. All the receptor afferents were non-medullated with conduction velocities from 0.5 to 1.5 m/s. Elevation of left atrial pressure during graded aortic occlusion always induced a marked increase in receptor discharge with maximal frequencies ranging from 29 to 70 Hz. The threshold for activation was from 7.5 to 13 mmHg in mean left atrial pressure (mean +/- S.E., 10.2 +/- 0.6 mmHg). Upon atrial distension all the receptors displayed a clear rhythmicity and the discharge correlated mainly with the v-wave, indicating distension as the cause of receptor activation. The relationship between the mean left atrial pressure and the frequency of discharge was constructed for all the receptors and compared with similar data obtained from normotensive control rats (NCR) (Thorén et al. 1979). It was then obvious that the left atrial receptors are reset in SHR probably secondarily to a decreased distensibility of the left atrium.