AJP - Heart and Circulatory Physiology, Vol 253, Issue 1 133-H137, Copyright © 1987 by American Physiological Society
Primary resetting of left atrial sensory endings in Dahl salt-sensitive rats fed a low-salt diet
P. Thoren, D. A. Morgan and A. L. Mark
Vagal afferent pathways contribute to vasomotor inhibition and renal sodium
handling by modulating sympathetic nerve activity in rats. Low pressure or
cardiopulmonary baroreflex inhibition of sympathetic nerve activity is
attenuated in normotensive Dahl salt-sensitive (S) rats fed a low-salt
diet. The aim of the study was to record activity in single-fiber vagal
filaments from left atrial endings in Dahl S and resistant (R) rats to
evaluate the mechanism for the attenuated low pressure baroreflex. Rats
were fed a low-salt diet (0.1% NaCl) for 5-7 wk. Seven Dahl R and six S
rats were anesthetized with urethan, and catheters were placed in the aorta
and left atrium. Single-fiber recordings were obtained from the right
cervical vagus. The relationship between left atrial pressure and receptor
discharge was obtained during graded aortic snaring. Mean threshold for
increased activation of the vagal afferents during volume expansion was
10.4 +/- 0.6 mmHg (means +/- SE) in S and 6.0 +/- 0.4 mmHg in R rats (P
less than 0.002). Pressure-discharge curves were significantly shifted to
the right in S rats. Maximal sensitivity of the endings expressed as delta
discharge/delta LAP was not significantly different in R vs. S, but the
right shift in threshold reduced the discharge of endings over a
physiological range of filling pressures. We also measured left ventricular
end-diastolic pressure (LVEDP) in conscious S and R rats to determine if
the resetting of left atrial sensory endings could be explained by elevated
left heart filling pressure.(ABSTRACT TRUNCATED AT 250 WORDS)
