Hypertension from chronic central sodium chloride in mice is mediated by the ouabain-binding site on the Na,K-ATPase α2-isoform.

A chronic increase in the concentration of sodium chloride in the cerebrospinal fluid (CSF) (↑CSF [NaCl]) appears to be critically important for the development of salt-dependent hypertension. In agreement with this concept, increasing CSF [NaCl] chronically by intracerebroventricular (icv) infusion of NaCl-rich artificial CSF (aCSF-HiNaCl) in rats produces hypertension by the same mechanisms (i.e., aldosterone-ouabain pathway in the brain) as that produced by dietary sodium in salt-sensitive strains. We first demonstrate here that icv aCSF-HiNaCl for 10 days also causes hypertension in wild-type (WT) mice. We then used both WT and gene-targeted mice to explore the mechanisms. In WT mice with a ouabain-sensitive Na,K-ATPase α(2)-isoform (α2(S/S)), mean arterial pressure rose by ~25 mmHg within 2 days of starting aCSF-HiNaCl (0.6 nmol Na/min) and remained elevated throughout the study. Ouabain (171 pmol/day icv) increased blood pressure to a similar extent. aCSF-HiNaCl or ouabain given at the same rates subcutaneously instead of intracerebroventricularly had no effect on blood pressure. The pressor response to icv aCSF-HiNaCl was abolished by an anti-ouabain antibody given intracerebroventricularly but not subcutaneously, indicating that it is mediated by an endogenous ouabain-like substance in the brain. We compared the effects of icv aCSF-HiNaCl or icv ouabain on blood pressure in α2(S/S) versus knockout/knockin mice with a ouabain-resistant endogenous α(2)-subunit (α2(R/R)). In α2(R/R), there was no pressor response to icv aCSF-HiNaCl in contrast to WT mice. The α2(R/R) genotype also lacked a pressor response to icv ouabain. These data demonstrate that chronic ↑CSF [NaCl] causes hypertension in mice and that the blood pressure response is mediated by the ouabain-like substance in the brain, specifically by its binding to the α(2)-isoform of the Na,K-ATPase.

Analysis of intracranial pressure during and after the infusion test in patients with communicating hydrocephalus.

The cerebrospinal fluid (CSF) infusion test is used to evaluate the dynamics of CSF circulation in patients with communicating hydrocephalus and is based on constant-rate infusion of the normal saline into cerebrospinal fluid space. The aim of the study was to refine methods of the analysis of intracranial pressure (ICP) recorded during and after the infusion test. The mathematical model of cerebrospinal fluid circulation was extended by the equation describing ICP decrease after the infusion. The nonlinear least-squares method of Levenberg-Marquardt was used to estimate the parameters describing the CSF compensatory mechanisms. Twenty-seven infusion tests were studied. Both phases of the test-the increase and the decrease of ICP-were recorded and the compensatory parameters were calculated for each of them. ICP often does not return to the resting level after the infusion test within the period equivalent to the time of infusion in all cases. In 20 tests the differences between post- and pre-infusion resting ICP (DeltaICP) was higher than 1 mmHg, which was considered as significant. The mean value of DeltaICP for 20 infusion tests was 3.0 +/- 0.7 mmHg. The cerebral elasticity evaluated during the infusion was greater than the elasticity estimated from the decreasing phase after the infusion (0.24 +/- 0.07 ml(-1) versus 0.14 +/- 0.03 ml(-1); p < 0.01).

Assessment of cerebrospinal fluid outflow conductance using constant-pressure infusion--a method with real time estimation of reliability.

The outflow conductance (C(out)) of the cerebrospinal fluid (CSF) system is a parameter considered to be predictive in selection for hydrocephalus surgery. C(out) can be determined through an infusion test. A new apparatus for performing infusion tests in a standardized and automated way was developed. The objective was to evaluate repetitiveness as well as to propose and evaluate a method for real time estimation of the reliability of individual C(out) investigations. Repeated investigations were performed on an experimental model simulating the CSF system, and on 14 patients with hydrocephalus. DeltaC(out), calculated as the 95% confidence interval of C(out), was introduced as an estimate of the reliability of individual C(out) investigations. On the model, no significant difference was found between DeltaC(out) and the actual C(out) variation in repeated investigations (p = 0.135). The correlation between the first and the second patient investigation was high (R = 0.99, p < 0.05), although there was a significant difference between the investigations (p < 0.05). The standard deviation of difference was 2.60 microl (s kPa)(-1). The repetitiveness of C(out) with the new apparatus was high, and DeltaC(out) reflected the reliability of each investigation. This feature has to be taken into account in every individual case, before making a decision or performing research based on measurements of C(out) in the future.

CSF and ECF glutamate concentrations in head injured patients.

Excitatory Amino Acids (EAAs) release has been considered to be neurotoxic in traumatic brain injury patients. Microdialysis samples of extracellular space (ECS) and high glutamate concentrations in cerebrospinal fluid (CSF) following Traumatic Brain Injury (TBI) have been documented. The objective of this study was to determine the correlation between EAA release in ECS and CSF in focal and diffuse injury. Head injury patients (GCS < or = 8, n = 16) admitted to Medical College of Virginia Hospital were instrumented for microdialysis collection of ECS samples. CSF samples were collected through the external ventricular drainage catheter at four hour intervals for the first four days following injury. As a control group, CSF was collected from normal pressure hydrocephalus patients (n = 6). Elevated glutamate levels were observed in both CSF and ECS following head injury. The average glutamate concentration in CSF (3.20 +/- 3.62 mumol/l) was significantly increased from control levels (1.13 +/- 0.49 mumol/l, p < 0.05). Comparison of CSF and extracellular fluid (ECF) samples showed that the glutamate concentrations were maximal on the first and second days and gradually decreased on days 3 and 4. On days 4, the level of the glutamate had remained elevated above the normal level.

Ovine fetal swallowing response to intracerebroventricular hypertonic saline.

In the near-term ovine fetus, systemic hyperosmolality stimulates dipsogenic responses. Putative systemic dipsogens (hypertonicity, angiotensin II) may initiate responses by stimulation of select cerebral circumventricular nuclei lacking a blood-brain barrier. To investigate whether central osmotic-dipsogenic mechanisms are functional in utero, fetal swallowing responses to intracerebroventricular (i.c.v.) hypertonic saline were examined. Five pregnant ewes with singleton fetuses (128 +/- 1 days gestation) were prepared with fetal lateral cerebral ventricle and vascular catheters, electrocortical (ECoG) electrodes, and electromyogram wires on the fetal thyrohyoid muscle, nuchal and thoracic esophagus, and diaphragm and studied for a minimum of 5 days postoperatively. After a 2-h basal period, fetuses received an i.c.v. infusion of artificial cerebrospinal fluid followed by successive 30-min infusions of hypertonic NaCl in artificial cerebrospinal fluid (500 and 700 mosmol/kgH2O). In response to the i.c.v. hypertonic NaCl infusions, fetal swallowing significantly increased (1.4 +/- 0.4 to 3.9 +/- 1.4 and 2.9 +/- 0.5 swallows/min low-voltage ECoG, respectively). Plasma arginine vasopressin levels increased, although the change was not statistically significant (9.1 to 24.2 pg/ml; P = 0.07), and there was no change in fetal plasma osmolality, sodium concentration, or ECoG activity. Together with previous studies, these results indicate that both central and systemic osmotic dipsogenic mechanisms are functional in utero.

Cerebrospinal fluid composition of cattle with endotoxin-induced mastitis treated with isotonic (0.9%) or hypertonic (7.5%) sodium chloride.

This study examined the safety of intravenous hypertonic saline in cattle with experimental gram-negative endotoxemia. Cerebrospinal fluid (CSF) composition was examined in five control cows and eight treated cows 24 hours after the intramammary infusion of 1 mg of endotoxin. Four of the endotoxin challenged cows were treated intravenously with isotonic (0.9%) sodium chloride and four cows were treated intravenously with hypertonic (7.5%) sodium chloride. Decreased CSF osmolality, and sodium and alpha globulin concentrations and increased CSF concentrations of beta globulin were observed in both endotoxin-challenged saline-treated groups. No CSF compositional differences were observed between endotoxin-challenged cows receiving isotonic or hypertonic saline. Although no cytologic or biochemical evidence of salt poisoning was observed in cows receiving hypertonic saline, significant changes were observed in the CSF composition of both endotoxin-infused saline-treated groups.

Role of NaCl cotransport in cerebrospinal fluid production: effects of loop diuretics.

Cerebrospinal fluid (CSF) is secreted primarily by the choroid plexus (CP) located in the cerebral ventricles. Although much is known about ionic composition of cisternal CSF, the mechanisms involved in secretion of CSF in mammals are still not understood. The main aim of this report is to critically review the role of NaCl cotransport carrier in CSF production. On the basis of the studies in the literature, a model for CSF production by the CP is proposed. In this model, CP cells are assumed to be equipped with an NaCl cotransport carrier located on the basolateral (blood-facing) membrane. Because Na+ and Cl- are the two principal ions in CSF, their continued secretions into cerebral ventricles by CP cells require an adequate intracellular supply, which may be guaranteed by the NaCl cotransport carrier. Although this appears to be a reasonable assumption, making the processes involved in CSF production similar to those of other secretory epithelial cells, the presence of such a carrier in mammalian CP remains controversial. The reasons for this controversy are critically reviewed, and some suggestions for further studies are made.

Reduction of cerebral NaCl concentration can abolish mineralocorticoid escape.

The effect of lowering cerebrospinal fluid (CSF) Na concentration on renal Na excretion (UNaV) was investigated in conscious sheep undergoing mineralocorticoid escape induced by intravenous infusion of aldosterone (20 micrograms.ml-1.h-1) for 3 days. On the 3rd day of aldosterone administration, when plasma and CSF Na concentration and mean arterial blood pressure (MABP) were increased as a result of the mineralocorticoid treatment, a reduction in the CSF Na concentration was induced by infusing a Na-free solution of 300 mmol/l mannitol (1 ml/h) into a lateral cerebral ventricle. This caused significant reductions in UNaV and MABP and a significant increase in renal free water clearance (CH2O). There was no significant change in glomerular filtration rate or plasma atrial natriuretic peptide concentration, but renal lithium clearance decreased. Simultaneous intravenous infusion of vasopressin (0.03 microgram/h) and lowering of CSF Na concentration also caused significant reductions in UNaV and MABP, but CH2O did not increase. We propose that increased Na concentration of brain fluid may initiate natriuretic and pressor mechanisms contributing to the process of mineralocorticoid escape. Reduced UNaV may have been due to reduced MABP, but it is unlikely to have been due to reduced plasma vasopressin levels.

Differential blood pressure responses to oral and central salt administration in two substrains of Dahl rats.

Studies were made on whether oral or intraventricular (icv) NaCl had different effects on the blood pressure (BP) of Dahl rats. Five groups of each strain of Dahl rats, salt-sensitive (S) and salt-resistant (R) rats, were given, respectively, a diet containing 0.3% and icv infusion of 0.15 mol/L NaCl (group 1, control group) or 0.8 mol/L NaCl (group 2), a diet containing 8% NaCl and icv infusion of 0.15 mol/L (group 3) or 0.8 mol/L NaCl (group 4) for 12 days, or an 8% NaCl diet and icv infusion of 5% glucose (group 5). The icv infusions were made into the third cerebral ventricle with an osmotic minipump. In the control group of S rats (group 1) the BP was 120 +/- 4 mm Hg, whereas the BP in groups 3, 4 and 5 were 154 +/- 4, 161 +/- 5 and 153 +/- 3 mm Hg, respectively, and that in group 2 was 142 +/- 3 mm Hg on day 12. In the R rat, group 2 and group 4 showed a significant increase in BP over that of the control group. Multivariate analysis (quantification I) of these data confirmed that the BP of S rats was more sensitive to oral salt loading and that of the R rat was more strongly influenced by central salt administration. These results indicate that the two substrains of Dahl rats show different BP responses to oral and central administrations of NaCl.

Sodium chloride depletion in a cat with fistulated meningomyelocele.

Decreased serum and CSF chloride concentrations were documented in a 5-year-old Manx cat referred for evaluation of anorexia. Inadequate chloride intake coupled with chloride loss through a fistulated meningomyelocele probably caused chloride deficiency. The inciting cause of anorexia was not determined. The cat was treated with 0.9% NaCl solution. Normal serum and CSF chloride concentrations were restored. Lumbar myelography was performed to delineate the meningocutaneous tract, which then was dissected surgically and was ligated. The cat's body attempted to maintain normal CSF chloride concentration even though the serum chloride concentration was decreased markedly. Calculations made on the basis of rate of CSF production, CSF chloride concentration, and duration of anorexia provided supportive evidence for an active transport system for chloride from plasma to CSF.

Hypernatremia in calves.

Hypernatremia (sodium chloride intoxication) is described in two calves due to presumed mixing errors of oral electrolyte solutions while undergoing therapy for neonatal diarrhea. The experimental induction of hypernatremia in two clinically normal calves is also reported. Physical findings in diarrheic calves included depression, weakness, dehydration, and diarrhea. Serum sodium concentrations were found to be 171.6 mEq/l and 208.0 mEq/l, respectively. Treatment with intravenous fluids was attempted in both cases, but one calf died after 6 hours and the other calf died after 2 days and exhibited periodic convulsions before death. Experimental induction with oral administration of 1 l of electrolyte concentrate, which contained approximately 2750 mEq sodium revealed that the normal calves would willingly consume the solution as mixed with milk and develop clinical signs of hypernatremia within 6 hours of administration. Serum sodium concentrations of 176.0 and 179.8 were found in the experimental calves and coincided with the onset of overt depression and weakness, at which time they were euthanatized. Cerebrospinal fluid electrolyte analysis paralleled the serum electrolyte alterations.

Naloxone effects on plasma vasopressin and oxytocin concentrations elevated by histamine, nicotine, isoproterenol and an acute increase in [NaCl] in cerebrospinal fluid.

Endogenous opioid peptides inhibit secretion of oxytocin during dehydration, hemorrhage and parturition and attenuate release of vasopressin by tail electroshock. Diverse agents were used to stimulate the hypothalamo-neurohypophysial system to investigate the hypothesis that if oxytocin (or vasopressin) release were inhibited by opioid peptides regardless of the stimulus, the site of opiate action may be in the final common pathway (i.e. the magnocellular neuron) or on pituicytes in the neural lobe. Using male Sprague-Dawley rats, we therefore investigated the effect of an opiate receptor antagonist, naloxone (5 mg/kg s.c.), on the plasma concentrations of oxytocin and vasopressin elevated by various pharmacologic stimuli, including histamine (10 mg/kg i.p.), nicotine (0.15 or 1.5 mg/kg i.p.), isoproterenol (30 or 120 micrograms/kg i.m.) and increased [NaCl] in cerebrospinal fluid (CSF; 10 microliter artificial CSF containing 1 M NaCl i.v.t.). Control animals received saline (0.85%) or artificial CSF (containing 0.16 M NaCl). Animals were decapitated 60 s (increases[NaCl] in CSF) or 10 min after the stimulus or vehicle. Vasopressin and oxytocin were extracted from plasma and quantified by RIA. The concentrations of oxytocin and vasopressin in plasma were elevated (p less than 0.05) by histamine, isoproterenol (30 and 120 micrograms/kg), increases[NaCl] in CSF, and nicotine at the higher (1.5 mg/kg) but not lower (0.15 mg/kg) dose. Naloxone increased further (p less than 0.05) the concentration of oxytocin in plasma after histamine, nicotine (0.15 and 1.5 mg/kg), isoproterenol (30 and 120 micrograms/kg) and increases[NaCl] in CSF. Naloxone also increased (p less than 0.05) oxytocin concentration in controls receiving CSF or saline.(ABSTRACT TRUNCATED AT 250 WORDS)

Drinking in the pigeon (Columba livia) in response to water deprivation and the influence of intracerebroventricular infusions of NaCl or sucrose solutions.

Pigeons were deprived of fluid for 24 hours then allowed access to water and a 2.7% NaCl solution, the intakes of both solutions during the subsequent 60 min were observed. In a second experiment hypertonic or isotonic solutions of NaCl or sucrose were infused ICV, starting 5 min before access to the solutions and finishing 10 min after access, and the consummatory behaviour observed. Pigeons rehydrated themselves after the period of deprivation with a volume of water equal to the weight lost during the deprivation. Pigeons never drank the hypertonic NaCl solution. ICV infusions of hypertonic or isotonic sucrose attenuated drinking in response to 24 hours water deprivation. Isotonic or hypertonic NaCl infused ICV, on the other hand, had no significant effect. Thus, in the pigeon, drinking in response to 24 hours of water deprivation appears to be controlled by one mechanism, possibly osmoreceptor in nature (with the permissive control of CSF sodium concentration), since the birds drank a volume of water equal to their weight loss and changes in CSF sodium concentration influenced drinking in a manner similar to that described previously for osmotically induced drinking in pigeons.

Cerebral mechanisms influencing renal sodium excretion in dehydrated sheep.

Reducing the cerebrospinal fluid concentration of NaCl by infusion into a lateral cerebral ventricle of isotonic solutions of 0.3 mol/l mannitol or sucrose at 1 ml/h for 2 h caused a large reduction in renal Na excretion in conscious sheep deprived of water for 24 or 48 h. Infusion of 0.3 mol/l mannitol into the lateral ventricle of water-replete sheep did not alter renal Na excretion but induced a water diuresis. These data indicate that during dehydration, renal Na excretion may be under the control of the brain. The pathway(s) from brain to kidney mediating this antinatriuretic effect are not known.

Potentiation of antidiuretic response to systemic angiotensin II by elevation of CSF NaCl concentration.

The antidiuretic effect of the simultaneous intracerebroventricular (ICV) infusion of 0.24 M NaCl (0.02 ml/min) and intravenous (i.v.) infusion of angiotensin II (12 ng/kg X min) was studied in hydrated goats, and was compared to the antidiuretic effects of the separate infusions. The combined infusions inhibited the water diuresis for 30 min, whereas the separate infusions only reduced the water diuresis by 25% (ICV NaCl) and by 50% (i.v. angiotensin). The combined infusions increased the urine osmolality on the average by 415%. Corresponding increases induced by ICV NaCl and by i.v. angiotensin were 100 and 160%. The results suggest that systemic angiotensin II and elevated CSF NaCl concentration interact and potentiate each other as stimuli for antidiuretic hormone secretion. It is postulated that this synergism may help to preserve body water in hypovolemic conditions associated with hyperactivity of the renal renin-angiotensin system.

Vasopressin release in response to intracerebroventricular L-alanine and L-arginine, and its dependence upon CSF NaCl concentration.

Influences on renal water, electrolyte, and arginine vasopressin (AVP) excretions of 1 h infusions (20 microliters/min) of a neutral (L-alanine) and two basic (L-lysine and L-arginine) amino acids into the lateral cerebral ventricle were studied in hydrated goats, and were compared to effects of control infusions of hypertonic (0.25 M) NaCl. L-alanine (0.11 M) dissolved in hypotonic NaCl caused more pronounced inhibition of the water diuresis and greater increase in AVP excretion than did the control infusions, but, in comparison to the latter, the responses developed very slowly. The effects were further delayed and were much attenuated when L-alanine was administered in isotonic glucose, but became considerably accentuated when isotonic NaCl was used as the solvent. L-lysine (0.09 M) in hypotonic NaCl did not inhibit the water diuresis or cause any apparent AVP release, whereas the corresponding L-arginine infusions caused inhibition of the water diuresis and increase in AVP excretion of approximately the same magnitudes and time courses as the control infusions. Like for L-alanine, these effects became accentuated when L-arginine was dissolved in isotonic NaCl, and became delayed and much attenuated when isotonic glucose was used as the solvent. L-arginine induced a more pronounced increase in renal Na excretion than did L-alanine and 0.25 M NaCl. Since transport together with Na (increasing the Na influx) generally is much more important for cellular uptake of neutral than of basic amino acids, the possibility is discussed that L-alanine here might have caused AVP release by increasing transmembrane Na transport of juxtacerebroventricular Na sensors regulating the AVP secretion--a suggestion supported by the lack of response to the basic L-lysine. The antidiuretic effect of the other basic amino acid, L-arginine, can not be explained along this line. However, with regard to the characteristic differences observed between the responses to L-alanine and L-arginine, the possibility is discussed that the latter might not have acted at a sensory level, but on the final neuronal link in the release of neurohypophyseal hormones, the hypothalamic neurosecretory cells. In contrast to L-alanine and L-arginine, L-lysine appeared to stimulate the appetite of the goats.

Effects of centrally administered endogenous opioid peptides on drinking behavior, increased plasma vasopressin concentration and pressor response to hypertonic sodium chloride.

Intracerebroventricular (i.v.t.) administration of beta-endorphin or leucine5-enkephalin inhibited drinking behavior, the pressor response and increased plasma vasopressin concentration stimulated by an acute elevation in CSF sodium chloride concentration (10 microliter, 1 M NaCl i.v.t.). These effects of endogenous opioid peptides were prevented by naloxone, indicating opiate receptors were required for the biologic response. Drinking behavior associated with regulatory stimuli operant during dehydration was also inhibited by opioid peptides. beta-Endorphin (i.v.t.) delayed the onset and/or reduced the volume of water consumed in response to hypertonic sodium chloride (relative cellular dehydration), polyethylene glycol (hypovolemia) and food-associated drinking behavior. Inhibition of drinking did not appear related to sensory-motor dysfunction as another motivated behavior, eating (onset, amount consumed) was unaffected by beta-endorphin. It is concluded from these results that centrally administered endogenous opioid peptides inhibit sodium chloride-stimulated cerebral mechanisms affecting blood pressure and hydration.

Nonpressor mechanisms in CNS-induced natriuresis.

Ventriculocisternal perfusion was performed in pentobarbital-anesthetized dogs. Perfusion of high Na (300 mM NaCl) artificial cerebrospinal fluid (CSF) (E) for 2 h was preceded by 2 h of control (C) and was followed by 2 h of recovery (R) during which normal (150 mM NaCl) artificial CSF was perfused. A time-control group was perfused with normal artificial CSF throughout C, E, and R. High sodium perfusion resulted in a marked natriuresis in each of nine animals and suppression of plasma renin activity. Theere were no simultaneous changes in mean arterial pressure, glomerular filtration rate, or renal plasma flow. Sodium excretion and plasma renin activity showed a slight gradual rise in the time-control group, but no significant differences were observed between the C and E periods; sodium excretion and plasma renin activity were similar in the high Na and time-control groups during C and R, but significantly different during E. It is concluded that when CSF sodium is elevated by perfusing artificial CSF, the resulting natriuresis and suppression of plasma renin activity are not caused by hemodynamic changes.

Evidence for the movement of fluid, macromolecules and ions from the brain extracellular space to the CSF.

This report examines the effect of decreasing serum osmolality on movement into the ventricular system of fluid and of test material injected into the brain. Trace quantities of 22NaCl and 125I-labeled cat serum albumin (CSA) were injected into cerebral white matter of cats. The rates of cerebrospinal fluid volume flow, and appearance of 22Na and 125I-CSA were measured in the effluent fluid using ventriculocisternal perfusion before and while serum osmolality was acutely decreased by the intravenous infusion of a 60 mOsm sucrose solution. As compared to the control period, at the end of the infusion serum osmolality decreased from 321 +/- 4.2 mOsm to 283 +/- 4.0 mOsm and CSF volume flow increased from 21.8 +/- 2.3 microliter/min to 54.9 +/- 4.1 microliter/min (means +/- S.E.). The slope of the regression line describing 22Na influx went from 1.04 to 1.79, while for 125I the slope went from 0 to 1.38. These results suggest that a common pathway may exist for the movement, through the brain and into the ventricular system, of water, ions and large molecules.