EXCITATORY SYMPATHETIC REFLEX IN NACL-SENSITIVE SPONTANEOUSLY HYPERTENSIVE RATS

We have previously demonstrated blunted reflex responses of lumbar sym pathetic nerve activity during volume expansion in NaCl-sensitive spon taneously hypertensive rats maintained on basal (1% NaCl) diets compar ed with NaCl-resistant spontaneously hypertensive rats, Wistar-Kyoto r ats, and Sprague-Dawley rats. The current study tested the hypothesis that chronic ingestion of a high (8%) NaCl diet further blunts cardiop ulmonary reflex function in the NaCl-sensitive spontaneously hypertens ive rat. After 3 weeks of a 1% or 8% NaCl diet, male rats of all four strains were instrumented with femoral arterial and venous cannulas an d lumbar nerve recording electrodes at 10 weeks of age. Two days later , conscious rats were infused with whole blood to expand blood volume. NaCl-sensitive spontaneously hypertensive rats maintained on a 1% NaC l diet had blunted responses of nerve activity to acute volume expansi on compared with control strains. NaCl-sensitive spontaneously hyperte nsive rats maintained on an 8% NaCl diet had increases in nerve activi ty responses to volume expansion. In a second experiment, the volume e xpansion protocol was repeated in anesthetized NaCl-sensitive spontane ously hypertensive rats that had been subjected to sinoaortic denervat ion after 3 weeks of a 1% or 8% NaCl diet. After sinoaortic denervatio n, an increase in nerve activity was again observed during volume expa nsion in animals fed the 8% NaCl diet. In animals fed the 1% NaCl diet , changes in nerve activity were variable. The excitatory response was significantly reduced after bilateral vagotomy. These studies suggest that blood pressure regulation in NaCl-sensitive spontaneously hypert ensive rats is a complex interaction of excitatory and inhibitory symp athetic reflex systems that is altered by high dietary NaCl exposure.