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University of Ottawa Heart Institute, Ottawa, Ontario K1Y 4E9, Canada
Both brain
ouabain-like activity ("ouabain") and brain angiotensin II (ANG
II) contribute to the sympathoexcitatory and pressor responses to high
sodium intake in spontaneously hypertensive (SHR) and Dahl
salt-sensitive (Dahl S) rats. To assess whether increases
in cerebrospinal fluid (CSF) sodium can mimic this pattern of changes,
Wistar rats were chronically infused with artificial CSF (aCSF) or
sodium-rich aCSF (0.8 or 1.2 M sodium) intracerebroventricularly through osmotic minipumps for 14 days. Sodium-rich aCSF
(0.8 M) was also infused intracerebroventricularly for 2 wk
concomitantly with either antibody Fab fragments that bind ouabain and
related steroids with high affinity,
-globulins as control (200 µg/day for both), or the AT1
blocker losartan (1 mg · kg
1 · day
1).
Sodium-rich aCSF increased CSF sodium from 146 ± 2 to 152 ± 2 (0.8 M) and 160 ± 3 (1.2 M) mmol/l, and increased brain
"ouabain" in the hypothalamus, pituitary, and pons. In conscious
rats, sodium-rich aCSF increased baseline mean arterial pressure (MAP),
enhanced MAP, heart rate (HR), and renal sympathetic nerve activity
(RSNA) responses to intracerebroventricular
2-adrenoceptor agonist
guanabenz and air stress, and desensitized arterial and cardiopulmonary baroreflex control of HR and RSNA. These effects were largely prevented
by intracerebroventricular Fab fragments or losartan. Thus, in Wistar
rats, both brain "ouabain" and the brain renin-angiotensin system
contribute to sympathoexcitation, impairment of baroreflexes, and
hypertension caused by chronically increased CSF sodium. The similar
patterns of changes caused by CSF sodium in Wistar rats and by high
sodium intake in SHR and Dahl S rats indicate that if high sodium
intake increases central sodium, such changes may contribute to
sympathoexcitation and hypertension.
cerebrospinal fluid sodium; baroreflex; sympathetic nerve activity; guanabenz
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