Effect of CSF dilution on the blood pressure of rats with renal hypertension

The concentration of many substances in cerebrospinal fluid (CSF) of hypertensive animals has been reported to be elevated but cause-effect relationships are unclear. Conscious adult male Sprague-Dawley rats were infused via a lateral cerebroventricle with artificial CSF or water (2 μl/min) or were not infused. Three groups of rats were tested: rats with renal hypertension (bilateral renal artery stenosis), sham-operated controls and unoperated controls. Blood pressures of the normotensive or hypertensive animals were unaffected by a 5-hour infusion of artificial CSF or water. Urinary output of rats infused with water was increased, indicating that water infusion was efficacious in diluting CSF. Based on experiments in anesthetized rats, we estimate that water infusion diluted CSF 8–14%. These results support the opinion that altered sensitivity to, or concentration of, CSF constituents per se does not maintain hypertensive blood pressures. Furthermore, it is unlikely that CSF serves as a conduit to deliver active substances to periventricular brain sites regulating blood pressure and hydration. Excess concentration of CSF constituents in hypertension probably reflects overflow into CSF instead of a cause-effect phenomenon.