RENAL RESPONSES TO HYPERTONIC SALINE INFUSION IN SALT-SENSITIVE SPONTANEOUSLY HYPERTENSIVE RATS

In Wistar Kyoto (WKY) and Sprague Dawley rats, high dietary sodium chl oride (NaCl) increases natriuretic and diuretic responses to acute iso tonic saline infusion, but in NaCl-sensitive spontaneously hypertensiv e rats (SHR-S), a high-NaCl diet causes negligible increases in natriu retic and diuretic responses. To investigate whether this deficit in s odium and fluid excretion in SHR-S is stimulus (volume)-specific or be cause of a more generalized alteration in renal function, the present study measured, in SHR-S and Wistar Kyoto rats, natriuretic and diuret ic responses to a hypertonic saline infusion (the amount of sodium inf used was equal to that infused in a previous, isotonic experiment). Ei ght-week-old Wistar Kyoto rats, SHR-S, and salt-resistant SHR were giv en a basal (1%) or high (8%)-NaCl diet for 2 weeks. Intravenous infusi on of hypertonic saline increased mean arterial pressure and reduced h eart rate in all groups. Baseline sodium excretion was lower in SBR-S compared with salt-resistant SHR with either diet, but; after infusion of hypertonic saline, all 6 groups displayed significant increases in sodium and fluid excretion, glomerular filtration rate, and effective renal blood flow (ERBF). The percent-sodium excretion in response to hypertonic saline infusion was slightly, but significantly, lower in S HR-S (compared with salt-resistant SHR) for either the basal or the hi gh-NaCl diet, We conclude that renal responses to hypertonic saline in fusion are affected minimally in SI-IR-S compared with sale-resistant SHR or Wistar Kyoto rats. Therefore, the deficits in renal function ob served in SHR-S after volume loading are not reflected in a renal defi cit to hypertonic saline challenge.