Increased dietary salt intake enhances the exercise pressor reflex.

Am J Physiol Heart Circ Physiol. 2014 Feb;306(3):H450-4. doi: 10.1152/ajpheart.00813.2013. Yamauchi K, Tsuchimochi H, Stone AJ, Stocker SD, Kaufman MP. People in this group have previously shown that high-salt diets can lead to altered sympathetic signaling in rats, but this time around they wanted to look and see if the diet caused changes in the exercise pressor reflex - which itself depends partly on the RVLM. They fed rats either 0.1% or 4.0% salt diets. Between groups there were no differences in arterial pressure or plasma levels of K, Na, or Cl. However, there was a near significant difference (p=0.06) in heart rate, with the high-salt diet causing a decrease. They then tested the effect of static hindlimb muscle contraction (via tetanic electrical stimulation of motor neurons in the ventral root) on blood pressure and heart rate and saw that rats fed a high-salt diet had enhanced increases in both categories. The increases in both groups were almost completely eliminated by cutting the muscle afferent nerves (L4 and L5 dorsal root denervation), indicating that these afferents are responsible f. To check to see if there was a change in response to sympathetic neural input, they stimulated the lumbar sympathetic chain at different frequencies. This produced frequency-dependent increases in arterial pressure and frequency-dependent decreases in femoral blood flow, and vascular conductance, but there was not a difference between groups. I guess that means that some salt-induced changes happen between the neurons feeding the skeletal muscle and the muscle itself, and that changes they've previously shown in the sympathetic system don't occur at the peripheral sites, but must occur centrally, like in the RVLM. -DH