ROLE OF RENAL NERVES IN MEDIATING THE BLUNTED NATRIURETIC RESPONSE TOACUTE SALINE LOAD IN OBESE DOGS

We previously reported that the natriuretic response to an acute sodiu m load is markedly attenuated in obese dogs. Since obesity is associat ed with enhanced sympathetic nervous activity, the purpose of this stu dy was to test the hypothesis that obese animals have a reduced abilit y to excrete a sodium load as a result of abnormal renal nerve functio n. To test this hypothesis, we,determined the effects of an acute sodi um load (100 mEq NaCl given as isotonic saline over 60 min) in lean (1 9.8 +/- 1.0 kg) and obese (25.8 +/- 1.1 kg) dogs. Two surgically desig ned hemibladders with indwelling catheters were used to collect urine from innervated (INN) and denervated (DNX) kidneys of the same dog. Ar terial pressure averaged 99 +/- 3 mm Hg in the obese dogs and 90 +/- 3 mm Hg in the lean dogs. In response to the saline loading in lean dog s, sodium excretion (UNaV) increased from 31.0 +/- 7.8 to 145.6 +/- 25 .9 mu Eq/min in the INN kidneys and from 43.1 +/- 10.6 to 151.1 +/- 28 .4 mu Eq/min in the DNX kidneys. In contrast, UNaV in obese dogs incre ased from 10.3 +/- 3.0 to 110.1 +/- 25.5 mu Eq/min in the INN kidneys and from 24.4 +/- 2.7 to 106.1 +/- 20.6 mu Eq/min in the DNX kidneys. Cumulative sodium excretory response to sodium loading was significant ly lower in the obese dogs. In addition, there was no difference in th e cumulative UNaV response between the INN (8.4 +/- 2.2 mEq) and DNX k idneys (9.1 +/- 2.3 mEq) of obese dogs. These data indicate that the n atriuretic response to an acute saline loading is markedly attenuated in obese dogs. Furthermore, factors other than renal nerves play a rol e in this abnormal response. (C) 1997 American Journal of Hypertension , Ltd.