Renal nerve activity in conscious rats during volume expansion and depletion

The role of renal nerve activity (RNA) in the renal response to isotonic saline volume expansion and furosemide-induced volume depletion was studied in conscious rats consuming a low (LNa), normal (NNa), or high (HNa) dietary sodium intake. In the control state, right atrial pressure (RAP) and UNa V were directly related and RNA was inversely related to dietary sodium intake, being 12.9 +/- 0.7, 10.9 +/- 1.1 and 8.7 +/- 0.6 units in LNa, NNa, and HNa rats, respectively. During volume expansion, RAP and UNa V increased and RNA decreased in all three dietary groups; however, the peak increase in UNa V was greater in the LNa (88 +/- 6 mueq/min) than NNa (34 +/- 9 mueq/min) or HNa (32 +/- 6 mueq/min) rats. The greater natriuresis in LNa was associated with a larger decrease in RNA in LNa (-6.1 +/- 0.5 units) than in NNa (-3.4 +/- 0.4 units). The greater contribution of inhibition of RNA to the increased natriuretic response to volume expansion in LNa compared with NNa rats was further examined in renal denervated animals. Bilateral renal denervation substantially reduced the natriuretic response to volume expansion in LNa rats (-70%) but had no significant effect in NNa rats (-15%). During volume depletion, RAP decreased, whereas UNa V and RNA increased in all three dietary groups. After the peak of the furosemide natriuresis, UNa V was lower in the LNa rats than in the NNa or HNa rats at any level of increased RNA, consistent with a role for the renal nerves in the normal renal adaptive response to sodium/volume depletion.(ABSTRACT TRUNCATED AT 250 WORDS)