AJP - Regulatory, Integrative and Comparative Physiology, Vol 244, Issue 2 264-R272, Copyright © 1983 by American Physiological Society
Effects of dietary sodium restriction on heart rate control in rats
E. N. Bush and R. R. Vollmer
The effects of dietary sodium restriction on heart rate control were
evaluated in male Wistar rats maintained for 4 wk on a low- (22 meq/kg
diet) or standard (141 meq/kg diet) sodium diet. In conscious low-sodium
rats, atropine produced heart rate increases greater than in standard
sodium animals, indicating that basal parasympathetic tone was elevated.
Sodium restriction did not affect basal sympathetic tone, since similar
reductions in heart rate were produced by propranolol in both dietary
groups. However, sympathetically mediated tachycardic responses to sodium
nitroprusside were augmented in low-sodium rats. This enhancement of
sympathetic function was also observed in low-sodium animals after pithing.
The increases in heart rate produced by spinal sympathetic stimulation were
significantly accentuated; whereas, responses to norepinephrine were not
affected by the diets. This finding is in agreement with the observation
that the chronotropic responses elicited by isoproterenol in isolated atria
were not altered. When neuronal influences on heart rate were blocked by
combined administration of atropine and propranolol or chlorisondamine in
conscious rats, the underlying intrinsic cardiac rate was found to be
significantly higher in low-sodium rats. In summary, the present study
identifies three effects of sodium restriction on heart rate control in the
rat: 1) basal parasympathetic tone is increased, 2) heart rate responses to
sympathetic activation are enhanced, and 3) the intrinsic cardiac rate is
elevated.
