Increases in CSF Na+ precede the increases in blood pressure in Dahl S rats and SHR on a high-salt diet

In Dahl salt-sensitive (S) and salt-resistant (R) rats, and spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats, at 5–6 wk of age, a cannula was placed in the cisterna magna, and cerebrospinal fluid (CSF) was withdrawn continuously at 75 μl/12 h. CSF was collected as day- and nighttime samples from rats on a regular salt intake (0.6% Na + ; R-Na) and then on a high salt intake (8% Na + ; H-Na). In separate groups of rats, the abdominal aorta was cannulated and blood pressure (BP) and heart rate (HR) measured at 10 AM and 10 PM, with rats first on R-Na and then on H-Na. On H-Na, CSF Na + started to increase in the daytime of day 2 in Dahl S rats and of day 3 in SHR. BP and HR did not rise until day 3 in Dahl S rats and day 4 in SHR. In Dahl R and WKY rats, high salt did not change CSF Na + , BP, or HR. In a third set of Dahl S rats, sampling of both CSF and BP was performed in each individual rat. Again, significant increases in CSF Na + were observed 1–2 days earlier than the increases in BP and HR. In a fourth set of Dahl S rats, BP and HR were recorded continuously by means of radiotelemetry for 5 days on R-Na and 8 days on H-Na. On H-Na, BP (but not HR) increased first in the nighttime of day 2. In another set of Dahl S rats, intracerebroventricular infusion of antibody Fab fragments binding ouabain-like compounds (OLC) with high affinity prevented the increase in BP and HR by H-Na but further increased CSF Na + . Finally, in Wistar rats on H-Na, intracerebroventricular infusion of ouabain increased BP and HR but decreased CSF Na + . Thus, in both Dahl S and SHR on H-Na, increases in CSF Na + preceded the increases in BP and HR, consistent with a primary role of increased CSF Na + in the salt-induced hypertension. An increase in brain OLC in response to the initial increase in CSF Na + appears to attenuate further increases in CSF Na + but at the “expense” of sympathoexcitation and hypertension.