Abstract
It has been unclear whether changes in renal sympathetic nerve activity (RSNA) influence chronic regulation of sodium excretion and arterial pressure because there is little information on the chronic effect of changes in RSNA on sodium excretion and arterial pressure. In the present study, a month recording of RSNA in freely moving rats was carried out to study the long-term regulation of RSNA and sodium excretion. Wistar rats were instrumented chronically with electrodes for the measurements of RSNA and electrocardiogram. At least 7 days after the implantation of the electrodes, the animals were housed in individual metabolic cage and then RSNA, heart rate and sodium balance were measured over three weeks. Animals were allowed to drink four different concentration of sodium chloride solutions; that was 0, 50, 154, 308 meq/l NaCl. The experiments were consisted of 3 days control (50 meq/l NaCl) period, 3 days unloading (0 meq/l NaCl)/loading (154, 308 meq/l NaCl) period, and 3 days recovery (50 meq/l NaCl) period. The sodium loading with 308 meq/l NaCl suppressed RSNA significantly over the 3 days loading period and then it recovered above the control level while either 0 meq/l NaCl and 154 meq/l NaCl loading had no effects on RSNA. Sodium excretion changed significantly in proportion to the sodium loading levels during 0, 154 and 308 meq/l NaCl. These results demonstrated that changes in RSNA were not always correlated with the changes in sodium excretion during 3 days sodium unloading/loading period in rats. [J Physiol Sci. 2006;56 Suppl:S205]
