A Pressor Substance in the Cerebrospinal Fluid of Normotensive and Hypertensive Patients

Abstract

A pressor polypeptide was isolated from the cerebrospinal fluid of normotensive and hypertensive patients. Pharmacologically it behaves like angiotensin I. A very significant correlation (r = 0.83, P < 0.001) was found between the concentration of this polypeptide and the blood pressure of essential hypertensive patients.Early theories about the pathogenesis of essential hypertensive disease claimed that neural mechanisms were involved. The classical experiments by Goldblatt and the discovery of the renin-angiotensin system abruptly switched the emphasis to the kidney (1), which has occupied since then a central position in all hypotheses advanced to explain the mechanism of essential hypertension. A link was sought in vain between the renin-angiotensin system and hypertensive disease. No correlation was found between the concentration of angiotensin in plasma and the blood pressure of essential hypertensive patients (2). At the same time pharmacological experiments showed that angiotensin II acts on central sympathetic structures, thereby inducing a prolonged increase of arterial blood pressure (3). These results have acquired a new physiological perspective after renin (4, 5), converting enzyme (6), and angiotensins I and II (4,7,8) were found in the central nervous system of rats and dogs, suggesting that the brain renin-angiotensin system might be involved in regulation of arterial blood pressure. These observations led to the search for pressor polypeptides in the cerebrospinal fluid of normotensive and hypertensive patients. This paper contains the first results of such a study. Isolation of the Pressor Material. 10 ml of cerebrospinal fluid (CSF) were obtained from each patient, and the samples were collected in siliconed tubes containing EDTA (final concentration 3 mM). In order to destroy eventual catecholamines that could invalidate the biological assays, the CSF sample was adjusted to pH 10 with 0.1 M NaOH and boiled for 20 min. After cooling, the pH was lowered to neutrality with 0.5 M HCl. Three to four volumes of ice-cold 96% ethanol were added, and the samples were left at 40 overnight.The precipitate was discarded by centrifugation, and the clean supernatant was concentrated in a vacuum rotatory evaporator to 0.5 ml, which was then applied to a 0.6 X 7 cm Dowex X-2 column equilibrated with 0.1 M phosphate buffer (pH 7.5). The column was washed with 5 ml of the buffer followed by 2 ml of water; the retained materials were eluted with 1.5 ml of 0.1 M NaOH and 4 ml of water, and this solution was neutralized with 0.5 M HCl. After concentration to 0.5 ml, the eluate was filtered through a Sephadex G25 (fine) column previously calibrated with 5-L-[U-14C]isoleucine-angiotensin II purchased from New England Nuclear. 0.5 M formic acid was used as eluant. The formic acid in the selected fractions was eliminated before the bioassays by repeated evaporations.Bioassay. Pressor activity was assayed on nephrectomized rats. Duplicate determinations were performed for each sample and repeated on at least...

Angiotensinogen levels in the brain and cerebrospinal fluid of the genetically hypertensive rat.

“…Although CSF levels were high, confirming previous reports, 5 the levels of CSF angiotensinogen did not correlate with brain levels. These findings support our earlier suggestion that the CSF is a sink for angiotensinogen 43 and indicate that CSF values may not provide an accurate reflection of the regulation of local brain angiotensinogen levels.…”

Components of the Renin-Angiotensin System in the Cerebrospinal Fluid of Rats and Dogs with Special Consideration of the Origin and the Fate of Angiotensin II

“…On the other hand, ANG II content in outflowing aCSF perfusate was found to be increased in conscious restrained rats [13] and native CSF of dogs ap pears to contain higher ANG levels when collected immedi ately after induction of anesthesia [20], The elevated ANG II levels measured in the CSF of the New Zealand strain [62] of spontaneously hypertensive rats (SHR) seem to contribute to the hypertension, since the blood pressure decreased after the intraventricular injection of the ANG II receptor antagonist saralasin [13]. It has also been reported that ANG-like material was increased in CSF of hyperten sive patients [8]. The blood pressure lowering effect of intra ventricular saralasin was confirmed in the Japanese strain [34] of stroke-prone SHR even when animals were nephrectomized 15-20 h previously [44].…”

Neuroendocrine components in the regulation of blood pressure and renin secretion.

“…However, the significance of such entry, if it does occur, is questionable, and the evidence for it is indirect. 27,30 'Values separated by a dash represent ranges. I = immunoassay; B = bioassay.…”