cerebrospinal fluid angiotensin II immunoreactivity is not derived from the plasma

Abstract

To elucidate whether the presence of angiotensin II immunoreactivity (ANG GH-ir) in the cerebrospinal fluid (CSF) of the dog is in part due to passage of the peptide across the C SF-blood-brain barrier, [He5] angiotensin II (ANG II) was infused intravenously for 7 days in conscious, trained dogs at a rateof 10 μg/kg/day. Mean arterial pressure (MAP) and heart rate were monitored each day, and samples of arterial blood and CSF (with a catheter secured into the cisterna magna) were drawn at regular intervals for determination or catecholamine levels, ANG H-ir, and electrolyte levels. Within 2 days after ANG II infusion, MAP stabilized at 35 ± 1 mm Hg (mean ± SE, p < 0.001) above control values. The hypertension was associated with bradycardia, suppressed plasma renin activity, and a fall in both plasma and CSF Na+concentrations. These changes coincided with a considerable and sustained decrease in the levels of plasma and CSF norepinephrine. On the other hand, levels of epinephrine and K+in the two compartments remained unchanged. Although concentration of ANG H-ir in plasma was augmented markedly (368% above control values, p < 0.001), ANG H-ir in the CSF remained within the low values measured in the control period. We conclude thai ANG H-ir in the CSF of the cisterna magna of the dog does not originate from and is not related to the concentration of the peptide in the plasma, even after considering a possible pressure-dependent increase in the permeability of the blood-brain barrier. These data provide further evidence that CSF ANG H-ir may be synthesized in brain tissue and may either be released or diffuse into the extracellular fluid contained in the brain ventricles. © 1985 American Heart Association, Inc.