Baroreflex impairment precedes hypertension during chronic cerebroventricular infusion of hypertonic sodium chloride in rats.
AUTOR(ES)
Buñag, R D
RESUMO
Osmotic minipumps were implanted chronically for continuous 11-d infusion of hypertonic sodium chloride (NaCl) into the third cerebral ventricle (ICV) of awake rats to determine whether baroreflex sensitivity would be altered. Systolic and mean pressures, recorded from aortic catheters on day 11 while the rats were anesthetized with alpha-chloralose, were significantly higher in rats infused with artificial cerebrospinal fluid (CSF) containing hypertonic NaCl than in controls similarly infused with artificial CSF alone. Reflex changes in heart rate produced by subsequent intravenous infusions of either phenylephrine or sodium nitroprusside were inhibited, but reflex changes in renal nerve activity were unaltered. Magnitude of reflex bradycardia during pressor responses to phenylephrine, as well as of reflex tachycardia during depressor responses to sodium nitroprusside, was consistently smaller in NaCl-infused than in control rats. By contrast, group differences in attendant renal nerve firing were not significant. After sinoaortic denervation, drug-induced blood pressure effects persisted, but reflex responses in heart rate and renal nerve firing were abolished or markedly diminished. Peripheral effects produced by hypertonic NaCl leakage from the infusion site were considered unlikely because after 11 d of ICV infusion, sodium concentration, though appreciably elevated in CSF samples collected from the cisterna magna, was unaffected in corresponding serum samples. When cardiovascular responses to phenylephrine were recorded while chronic ICV infusions were in progress, awake rats receiving hypertonic NaCl were still normotensive on day 2 yet reflex bradycardia was already attenuated. In showing that baroreflex impairment preceded the development of hypertension, our results suggest that by depressing the anterior hypothalamus, chronic ICV infusion of hypertonic NaCl reduces sympatho-inhibition, and the ensuing baroreflex impairment then elevates blood pressure. However, other mechanisms could also be involved.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=425396Documentos Relacionados
- Sodium status influences chronic amphotericin B nephrotoxicity in rats.
- Chronic caffeine administration exacerbates renovascular, but not genetic, hypertension in rats.
- Acute AT1 receptor blockade does not improve the depressed baroreflex in rats with chronic renal hypertension
- Baroreflex sensitivity in hypertension during beta-adrenergic blockade.
- Facilitation of the arterial baroreflex by the preoptic area in anaesthetized rats.