Further evidence for the importance of CSF Na+ concentration in central control of fluid balance

The neural basis of homeostatic and anticipatory thirst

Water intake is one of the most basic physiological responses and is essential to sustain life. The perception of thirst has a critical role in controlling body fluid homeostasis and if neglected or dysregulated can lead to life-threatening pathologies. Clear evidence suggests that the perception of thirst occurs in higher-order centres, such as the anterior cingulate cortex (ACC) and insular cortex (IC), which receive information from midline thalamic relay nuclei. Multiple brain regions, notably circumventricular organs such as the organum vasculosum lamina terminalis (OVLT) and subfornical organ (SFO), monitor changes in blood osmolality, solute load and hormone circulation and are thought to orchestrate appropriate responses to maintain extracellular fluid near ideal set points by engaging the medial thalamic-ACC/IC network. Thirst has long been thought of as a negative homeostatic feedback response to increases in blood solute concentration or decreases in blood volume. However, emerging evidence suggests a clear role for thirst as a feedforward adaptive anticipatory response that precedes physiological challenges. These anticipatory responses are promoted by rises in core body temperature, food intake (prandial) and signals from the circadian clock. Feedforward signals are also important mediators of satiety, inhibiting thirst well before the physiological state is restored by fluid ingestion. In this Review, we discuss the importance of thirst for body fluid balance and outline our current understanding of the neural mechanisms that underlie the various types of homeostatic and anticipatory thirst.

Various irrigation fluids affect postoperative brain edema and cellular damage during experimental neurosurgery in rats

BACKGROUND

This study was conducted to investigate how various irrigation fluids used during neurosurgical procedures affect the degree of postoperative brain edema and cellular damage during experimental neurosurgery in rats.

METHODS

The cerebral cortex was exposed and incised crosswise with a surgical knife under irrigation with an artificial CSF, lactated Ringer's solution, or normal saline. Four hours after injury, irrigation was stopped and brain tissue samples were obtained from injured and uninjured sites. Specific gravity, cerebrovascular permeability, and TTC staining of the samples were evaluated. Incision and irrigation of the brain were not performed on the control group.

RESULTS

At the injured site, specific gravities of the samples in the normal saline group and the lactated Ringer's solution group were significantly lower than the specific gravity in the artificial CSF group. The EB concentration was significantly higher in the lactated Ringer's solution group and relatively high in the normal saline group as compared with the artificial CSF group. TTC staining did not differ significantly between the artificial CSF group and the control group. It was significantly lower in the lactated Ringer's solution group and the normal saline group than in the control group and the artificial CSF group.

CONCLUSIONS

As compared with normal saline and lactated Ringer's solution, artificial CSF reduced postoperative brain edema, cerebrovascular permeability, and cellular damage in sites injured by experimental neurosurgery in rats.

Possible harmful effects on central nervous system cells in the use of physiological saline as an irrigant during neurosurgical procedures

BACKGROUND

Physiologic saline is routinely used as an irrigant in neurosurgery especially in Japan. Cerebrospinal fluid (CSF) differs from physiologic saline in its concentration of inorganic salts, osmolality, and pH and is completely different insofar as it contains glucose, protein, cholesterol, and other lipids. The present study was designed to compare the possible functional and morphologic deleterious influence of these differences on cultured rat neural cells using saline (S), Ringer's solution with glucose (Lactec G, LG; Otsuka Pharmaceutical Co.; Tokyo, Japan) and without glucose (Lactec, L; Otsuka Pharmaceutical Co.), and an artificial CSF (ACSF).

METHODS

Primary cultured rat neurons and astrocytes were divided into five groups according to the medium used, the four experimental groups (ACSF, L, LG, and S) and one control group (C). At various time points up to 24 hours, the rhodamine 123 uptake by neuronal or astrocytic cellular mitochondria was evaluated as cell function assessment. Morphologic assessment for both neuron and astrocyte culture was carried out with scanning electron microscopy (SEM) at the 24-hour time point.

RESULTS

SEM showed little difference between the C and ACSF groups, whereas morphologic deterioration was particularly severe in the S group for both neurons and astrocytes. In the case of neuronal mitochondrial activity, the L and S groups demonstrated respectively severe and some deterioration, particularly in the mitochondria of the neuronal processes. The deleterious effects in mitochondrial activity of the S group were even more apparent in the astrocytic cells.

CONCLUSION

These results suggest that physiologic saline, when used as an irrigant in neurologic surgery, might in some circumstances cause damage to exposed and compromised neural cells.

Reducing brain sodium concentration prevents post-prandial and dehydration-induced natriuresis in sheep

Renal Na excretion during the 24 h following feeding was studied in sheep. A pronounced natriuresis occurred 3.5-5.5 h after feeding. Na excretion then fell to low levels in animals allowed to drink water, but was significantly elevated above this level in water-deprived sheep for most of the remaining period. Both the post-prandial and dehydration-induced natriuresis were prevented by intracerebroventricular (icv) infusions of low Na concentration 0.3 mol l-1 mannitol at 1 ml h-1, and a water diuresis also occurred. These effects were not caused by icv infusion of artificial cerebrospinal fluid (Na concentration = 150 mmol l-1). As a result, there was a much greater increase in plasma Na concentration and osmolality in the sheep given icv mannitol. Intravenous infusion of vasopressin prevented the water diuresis induced by icv mannitol, but the inhibition of natriuresis was still observed and plasma Na concentration increased by 8 mmol l-1 over 24 h compared with an increase of 3 mmol l-1 in dehydrated sheep infused icv with artificial cerebrospinal fluid. The results show that the ambient Na concentration in the brain plays an important role in the normal homeostatic regulation of Na balance by the kidney in sheep.

Hyponatraemia in neurosurgical patients: diagnosis using derived parameters of sodium and water homeostasis

Seventeen unselected, consecutive patients with intracranial disease and accompanying hyponatraemia were studied. All would previously have been diagnosed as having the syndrome of inappropriate antidiuretic hormone (ADH) secretion on the basis of spot plasma/urinary electrolyte testing with the application to them of existing standard laboratory criteria. Timed urinary collections and matching plasma samples were available in all but three cases for the derivation of creatinine, osmotic and free-water clearances, tubular reabsorbed water, and fractional water and sodium excretions. In a number of patients the plasma renin, aldosterone and ADH levels were also assayed. On the basis of the overall findings, 13 patients were diagnosed as in fact having a salt-wasting state whilst in only four patients was the diagnosis of inappropriate ADH secretion (SIADH) substantiated. It is suggested that obtaining simple derived parameters of sodium and water homeostasis can add significantly in differentiating between these quite opposite syndromes.

Evidence for an influence of CSF sodium concentration upon ACTH-mediated cortisol response to intravenous and intracerebroventricular angiotensin II

The influence of cerebrospinal fluid (CSF) NaCl concentration upon the cortisol release induced by intracerebroventricular (i.c.v.) and intravenous (i.v.) infusions of angiotensin II (AII) was studied in conscious goats. A first series of experiments involved i.c.v. infusion (20 min; 20 microliters min-1) of simply hypertonic (0.5 M) NaCl, or of AII (2 pmol kg-1 min-1) dissolved in 0.5 M or isotonic (0.15 M) NaCl or in isotonic glucose. The most pronounced rise in plasma cortisol concentration (PC) was elicited by AII in 0.5 M NaCl, but responses of nearly the same size were obtained by merely 0.5 M NaCl and by AII in isotonic NaCl, whereas AII in glucose induced a smaller PC rise. An urge to drink developed during all infusions, except during the AII/glucose infusion. Here, however, thirst became apparent 2-6 min post-infusion. When, in a second series, the hypertonicity of the NaCl was reduced to 0.3 M, and the dose of AII to 0.5 pmol kg-1 min-1, only the infusion of AII in 0.3 M NaCl elicited any appreciable rise in PC. The response was approximately the same size as that earlier obtained as the effect of the larger dose of AII dissolved in isotonic saline. In a third series of experiments, a 30-min i.c.v. infusion of isotonic glucose, preceding and out-lasting a 10-min i.v. infusion of AII (40 pmol kg-1 min-1), was found to extinguish the rise in PC obtained as the effect of a separate i.v. infusion of AII.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations of ventricular pH alter water intake and food consumption in rats

The pH of third ventricular CSF was altered by infusing acidic or alkaline solution of artificial cerebrospinal fluid (aCSF) through chronically implanted stainless steel cannula. In two separate group of rats (n = 18 each) water and food consumptions were recorded 30 min, 1 hr, and 24 hr after intraventricular infusions of the modified aCSF solutions having pH 6.0, 8.0 and 7.4 (control). On raising the CSF pH, water intake increased in all three observations. Feeding was not affected in the observations taken after 30 min and 1 hr, but significantly reduced food consumption was observed 24 hr after the infusions. Lowering of pH had no effect either on dipsogenic or feeding response. The CSF pH correlated positively with drinking in all three observations. Since dipsogenic and feeding responses are centrally regulated by ion sensitive cells, it may be presumed that altered CSF pH influenced the activities of the sensors by altering ionic conductance across their membranes.

Cerebral regulation of renal sodium excretion in sheep infused intravenously with hypertonic NaCl

1. The natriuretic response to intravenous infusion of 2 M-NaCl was investigated in six conscious sheep. This hypertonic NaCl load resulted in relatively small, physiological (2-3 mmol l-1) increases in plasma Na+ concentration and was followed by a natriuresis with a maximum mean urinary sodium excretion 5 times higher than pre-infusion values. 2. Intravenous infusion of isotonic NaCl, delivering the same Na+ load as hypertonic NaCl infusion, did not induce natriuresis. This suggested, therefore, that with the hypertonic sodium load administered in the present study, the rise in plasma Na+ and/or tonicity rather than increase in blood volume is important in evoking the natriuretic response. 3. Intracerebroventricular infusion of low-Na+ artificial cerebrospinal fluid (CSF) reduced CSF Na+ concentration, decreased plasma vasopressin (AVP) levels and caused a copious water diuresis. This was associated with excessive loss of water and large increases in plasma Na+ concentration and osmolality. 4. The natriuresis induced by intravenous hypertonic NaCl load could be blocked by lowering CSF Na+ concentration in situations where water diuresis was either prevented or reduced by intravenous infusion of AVP or by delayed intracerebroventricular infusion of low-Na+ CSF, respectively. 5. The results of the present study provide further evidence that renal sodium excretion can be controlled by the central nervous system.

Intracerebroventricular saccharide infusions inhibit thirst induced by systemic hypertonicity

The effect of intracerebroventricular (i.c.v.) infusion of various iso- and hypertonic saccharide solutions on water intake stimulated by intracarotid (i.c.) infusion of hypertonic NaCl was studied in sheep. Without an i.c.v. infusion, water intake during a 10-min period following an i.c. infusion of 4 M NaCl (1.4 ml/min over 20 min) was 1.5-2.0 litres. I.c.v. infusion of all saccharide solutions (made up in artificial cerebrospinal fluid (CSF) with no Na) tested, 0.27 or 0.7 M D-glucose, L-glucose, 2-deoxyglucose and sucrose, decreased (35-65%) water intake. In general, there was little or no difference in antidipsogenic effectiveness between the isotonic and the hypertonic solutions or between the different saccharides used. I.c.v. infusion of artificial CSF ([Na] = 150 mM) did not alter water intake. CSF [Na] was decreased by all of the saccharide infusions. CSF osmolality was increased by the hypertonic solutions, was decreased by the artificial CSF and was unchanged by the isotonic solutions infused. The observation that the antidipsogenic effectiveness of saccharides which readily cross the blood-brain barrier (BBB; D-glucose, 2-deoxyglucose) was similar to that of saccharides which do not readily cross the BBB (sucrose, L-glucose) contrasts with effects reported on sodium appetite and suggests that the Na sensors involved in the inhibition of hypertonic NaCl-stimulated water intake are located close to or on the surface of the brain ventricular system, i.e. are responsive to changes in CSF [Na].(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of central hypersomotic solutions on drinking and vasopressin release following peripheral hyperosmotic NaCl in the minipig

The drinking and lysine vasopressin (LVP, porcine vasopressin) responses were measured in minipigs given simultaneous intracarotid (i.c.) (1.28 ml/min) and intracerebroventricular (i.c.v.) (50 microliters/min) infusions of solutions of differing osmolality and sodium content. Observations were made during, and for a further 15 min after, the combined infusions which lasted 15 min. Drinking in response to i.c. infusion of 2.0 Osm NaCl started with a latency of 7 min and was unaffected by simultaneous i.c.v. infusion of 0.15 M NaCl, was additive with the drinking produced by i.c.v. 1.4 Osm NaCl, sucrose or mannitol, and inhibited by i.c.v. infusion of 1.4 Osm urea. LVP release following i.c. hyperosmotic NaCl was observed as early as the first blood sample, at 2 min, and was attenuated by i.c.v. hyperosmotic urea and attenuated, then slightly augmented, by i.c.v. infusions of the hyperosmotic non-electrolyte solutions. These results show that drinking following peripheral administration of an osmotic stimulus in the minipig can add to that induced by central infusions of solutions that would have increased the effective osmotic pressure of the cerebrospinal fluid (CSF) but may have increased or decreased CSF sodium concentration. By contrast, the stimulated LVP release was attenuated by solutions that decreased CSF sodium concentration. Thus, in minipigs, separate osmoreceptors appear to mediate osmotically induced drinking and LVP release.

Lack of evidence for a cerebral sodium modulating mechanism in the monkey

Experiments were carried out in seven conscious macaque monkeys undergoing a water diuresis to determine the effects of raising carotid blood sodium concentration on renal sodium excretion and free water clearance. On separate days each animal received an intracarotid infusion of hypertonic sodium chloride (90 Eq NaCl/kg.body wt./min) for 5 to 10 min, the same hypertonic infusion intravenously, and an intracarotid infusion of isotonic NaCl. None of the infusions produced a change in sodium excretion. However, the intracarotid hypertonic infusion produced a sustained decrease in free water excretion while the other infusion did not. Creatinine clearance was not affected by any of the infusions. The results of these experiments support the view that while the brain of the primate contains an osmotic sensing mechanism it does not contain a mechanism which modulates sodium excretion.

Inhibition of dehydration induced drinking in rats by reduction of CSF Na concentration

Male rats were dehydrated for 22 h and then given 4 h intracerebroventricular (i.c.v.) infusions which commenced 2 h prior to the beginning of a 2-h fluid access period. I.c.v. infusion of iso-osmotic 0.27 M mannitol-CSF more than halved the amount of water normally drunk by dehydrated rats during the fluid access period. Whilst i.c.v. infusion of 0.7 M mannitol-CSF did not alter the amount of water drunk during the fluid access period. Presumably both infusates reduce CSF [Na] but only 0.7 M mannitol elevates CSF osmolality. The evidence is consistent with the involvement of both sodium and osmoreceptors in thirst in the rat. A reduction of CSF [Na] will inhibit dehydration induced water drinking provided the osmotic pressure of the CSF is not greatly elevated. In addition evidence is provided to show that a contrived reduction of CSF [Na] alone is not a sufficient physiological trigger to initiate salt appetite in rats.

Water drinking caused by intracerebroventricular infusions of hypertonic solutions in cattle

Infusions into the lateral cerebral ventricle of hypertonic solutions of NaCl, mannitol or sucrose all induced water drinking in cattle. However, infusion of hypertonic NaCl caused a significantly greater water drinking response than did the infusions of mannitol or sucrose, despite the fact that CSF osmolality increase was similar. In contrast, hypertonic solutions of NaCl or mannitol had similar dipsogenic effects when infused intravenously. The intracerebroventricular infusions of hypertonic NaCl or mannitol did not affect the intakes of food or Na solution. The results are consistent with the hypothesis that both cerebral osmoreceptors and Na sensors are involved in regulating thirst in cows.

The influence of central infusions on drinking due to peripheral osmotic stimuli in the pigeon (Columba livia)

The drinking responses of pigeons infused simultaneously IV (0.334 ml/min) and ICV (2 microliters/min) for 15 min with various osmotic solutions were observed during, and for 60 min after, the combined infusions. Drinking in response to IV infusion of 0.5 M NaCl or 1.0 M sucrose was unaffected by simultaneous ICV infusion of 0.15 M NaCl, enhanced by ICV 0.3 M NaCl, inhibited during the infusion of water ICV and attenuated by ICV infusion of 0.9 M sucrose. Drinking in response to IV infusion of 1.0 M NaCl or 1.5 M sucrose, two solutions that would have greatly increased CSF sodium concentration, was only slightly affected by simultaneous ICV infusions of NaCl, sucrose or water. These results show that drinking following IV administration of osmotic stimuli can be affected by ICV infusions that may have further increased or decreased CSF sodium concentration thereby suggesting that CSF sodium concentration may play a "permissive role" in osmotically induced drinking.

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.

Osmoregulation of thirst and vasopressin secretion in human subjects: effect of various solutes

Various hypertonic solutions were infused in healthy human volunteers to determine their effect on thirst and vasopressin secretion. Hypertonic saline and mannitol produced prompt and parallel increases in plasma osmolality and vasopressin concentration. For both of these solutes, there was a high degree of correlation between these measurements. The slope describing this relationship varied considerably between individuals, but the same subjects showed similar slopes with either saline or mannitol. Both solutions stimulated thirst. Hypertonic urea infusions produced a comparable rise in osmolality but produced a smaller increase in plasma vasopressin and stimulated thirst in only one of the subjects. With urea, the correlation between plasma osmolality and vasopressin was significantly lower. Within individuals, the slope describing this relationship was significantly correlated with that seen during hypertonic saline. Hypertonic glucose significantly increased plasma osmolality but decreased plasma vasopressin and had no detectable effect on thirst. We conclude that osmoregulation of vasopressin in humans is mediated by a selective osmoreceptor that is located primarily outside of the blood-brain barrier and that individual differences in osmoregulatory sensitivity are not solute specific.

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.

The relation between carotid solute concentration and renal water excretion in conscious dogs

Verney's hypothesis of cerebral osmoreceptors controlling the renal excretion of water via vasopressin was reinvestigated in conscious trained dogs provided with bilateral skin loops containing the common carotid arteries. In multiple experiments in two dogs, bilateral intracarotid injections (0.25 ml. (kg b.wt.)-1 per artery in 10 s) of a hyperosmotic solution of sodium chloride (0.257 mol/l) during transient water diuresis failed to produce an antidiuretic response, although it is estimated that the injections elevated the osmolality of the carotid blood by 12-15%. In another 5 dogs, Bilateral intracarotid infusions of hyperosmotic saline (45 mumol.(kg b wt..min)-1 per artery for 10 min) during sustained water diuresis resulted in a 3% increase in jugular venous osmolality and an antidiuretic response without detectable changes in heart rate or mean arterial pressure. Equal intravenous hyperosmotic or intracarotid isosmotic infusions were not associated with antidiuretic response. Analysis of the concomitant concentrations of vasopressin in plasma fell short of supporting the hypothesis that the antidiuretic response to intracarotid hyperosmotic infusions was exclusively or mainly due to liberation of vasopressin, although the renal response could be mimicked by exogenous vasopressin. It is concluded that the present results-although discordant with several of Verney's results and assumptions-nevertheless support the concept of a cerebral solute receptor influencing the rate of renal water excretion.

Intracerebroventricular osmosensitivity in the Pekin Duck. Properties and functions in salt and water balance

Pekin ducks were implanted with devices allowing intracerebroventricular (i.c.v.) microinfusions at rates of 0.1--0.4 mul/min during 15 min in the conscious animals. When hydrated by intragastric infusion of 1 ml/min tap water, i.c.v. infusion of hypertonic NaCl solutions reduced urine flow and increased osmolality, presumably due to increased ADH release. Osmotically equivalent Li+ salts (Cl-, Br-, So24-) caused a slightly prolonged antidiuresis, while Ca2+ and Mg2+ salts caused a more protracted antidiuresis. Urea solution osmotically equivalent to 4.8% NaCl had no effect on diuresis, while osmotically equivalent mannitol solution slightly enhanced diuresis. Angiotensin II (0.5--2.5 pmol in 15 min) and Carbachol (3.0 pmol in 15 min) infused in 0.9% saline caused antidiuresis. The results suggest that the central control of ADH release in birds is similarly organized as in mammals, with receptive elements reacting to ionic rather than osmotic changes and with Na+ as the naturally involved cation. In ducks with their salt glands activated by i.v. infusion of 800 mosmol NaCl/kg H2O at 0.2 ml/min, salt gland secretion was not augmented by i.c.v. microinfusion of hypertonic NaCl but inhibited by i.c.v. infusion of osmotically equivalent mannitol solution. The supraorbital salt glands, when activated appear to be little stimulated further by a rise but may be inhibited by a fall of i.c.v. Na+ concentration.

Inhibition of water intake by ouabain administration in sheep

Intracarotid infusion of ouabain (1280 ng/min) over 4 1/2 hr virtually abolished water intake of sheep in response to intracarotid infusion of either angiotensin II (800 ng/min) or 4 M NaCl (1.6 ml/min for 20 min. Ouabain treatment did not affect mean arterial pressure either before or during infusion of angiotensin. Neither ouabain nor angiotensin administration affected plasma [Na] or [K] or CSF [K]. During ouabain, but not during control infusion, angiotensin administration significantly decreased CSF [Na]. Ouabain administration also decreased water intake after 23 1/2 or 48 hr water deprivation. In the 23 1/2 hr deprivation experiments, food was made available immediately prior to water presentation and the ingestion of food appeared to ameliorate the reduction in water intake. Food intake itself, was decreased in some animals, during ouabain treatment. Ouabain infused at 960 ng/min resulted in significant, but smaller, reductions in water intake induced by angiotensin, 4 M NaCl, and 48 hr water deprivation. It was concluded that ouabain treatment affected water intake by influence on Na transport either in the thirst receptors or at some other level in the neural system between receptor and effector.

Deuterium induced extinction of ADH-release in response to intracerebroventricular infusions of hypertonic NaCl and angiotensin

Infusions (20 microliter/min) of hypertonic (0.3 M) NaCl and angiotensin II (1 ng/kg min-1) in isotonic (0.15 M) NaCl were made for 1 h in the hydrated goat during fully developed water diruesis. Either H2O or deuterium (D2O) WAS USED AS SOLVENT. A pronounced antidiuretic response, outlasting the infusion period by 30 min or more, was seen when the substances were dissolved in H2O. Only a weak inhibition of the water diuresis, which was extinguished during the infusion period, was obtained when D2O was used as the solvent. The infusion of 0.3 M NaCl/H2O invariably induced drinking in one of the goats, which, however, showed no drinking response to the infusions of 0.3 M NaCl/D2O. The possibility is discussed that D2O (perhaps by its inhibitory effect on (Na+-K+)-ATPase activity) reduced the sensitivity of juxtaventricular receptors regulating ADH-release and water intake.

Renal renin output during continuous intracarotid infusions of iso- and hypertonic sodium chloride solutions in the rat

On male Sprague Dawley rats isotonic NaCl during control and 1 M NaCl were infused either into the carotid artery or i.v. Glomerular filtration rate, sodium output and plasma renin activity were determined. Five of 19 animals reacted with no increase in sodium output for 1 M NaCl and are treated as a different group from the animals reacting with an increased sodium output. For the animals reacting with an increased sodium output a decrease in plasma renin activity was found together with an increase in glomerular filtration rate. In both groups the plasma sodium was constant. The animals not reacting with an increased sodium output had a higher initial plasma renin activity, which did not change during 1 M NaCl infusion. The responses were equal for both intracarotid and i.v. infusions but with a somewhat longer delay before the response occurred with i.v. infusions. These results might be explained by a central nervous effect and by a direct renal effect. Also during 1 M NaCl infusion a possible extracellular volume expansion, derived from water withdrawal from the cells into the extracellular space might occur.

Studies of cerebral osmoreceptors in anesthetized dogs: the effect of intravenous and intracarotid infusion of hyper-osmolar sodium chloride solutions during sustained water diuresis

The function of the suggested hypothalamic osmoreceptors was investigated in dogs during light chloralose anesthesia. The dogs were subjected to an i.v. load of 40 ml/kg b.w.t. of a hypo-osmolar solution of sodium chloride and glucose. This degree of hydration was kept constantly by a specially constructed servo system based on the weight of the animal. During water diuresis the renal free water clearance remained essentially constant for several hours (mean about 0.2 ml/kg b.w.t. min). Renal sodium excretion was low (mean 0.82 mumol/kg b.w.t. min) and decreased continuously throughout the experimental period. I.v. infusion of hyperosmolar sodium chloride solution (1.33 mmol/kg b.w.t. in 30 min) was followed by prolonged parallel increases in free water clearance and sodium excretion, without any detectable change in the excretion of osmoles and potassium. The renal response to bilateral infusion of hyper-osmolar NaCl (1.33 mmol/kg b.w.t. in 30 min) into the common carotid arteries was identical to the response to i.v. infusion. The estimated increase in the osmolality of the carotid blood was 2.2%. In seven out of eight experiments intracarotid infusion of NaCl (1.33 mmol/kg b.w.t. in 8 min) did not elicit any reduction in free water clearance. On the contrary, an increase was found similar to that obtained after i.v. infusion. The estimated increase in the osmolality of the carotid blood was 8.4%. The present results question the validity of the currently held view that hypothalamic osmoreceptors play an important role in the control of the osmolality of plasma.

Duration of central action of angiotensin II estimated by its interaction with csf Na+

In pre-hydrated goats, an urge to drink persisted for approximately half an hour after combined infusions of angiotensin II and hypertonic (0.5 M) NaCl into the lateral or third cerebral ventricle. The intraventricular infusion of angiotensin/glucose solution, having no dipsogenic action of its own, markedly accentuated the dipsogenic and antidiuretic effects of the subsequent intraventricular infusion of hypertonic NaCl. The possibility is discussed that angiotensin may be bound at periventricular receptor sites where it continues to interact with Na+ in eliciting thirst and ADH release for about half an hour.

Influence of intracranial osmotic stimuli on renal nerve activity in anaesthetized cats

In baroreceptor denervated cats one internal carotid artery (ICA) or the cerebral ventricular system (CVS) was perfused with isotonic, hypertonic and hypotonic sodium chloride solutions. Renal sympathetic activity (RSA) and blood pressure (BP) were recorded. ICA perfusion with isotonic sodium chloride (150 mM NaCl) produced no changes of RSA compared to control level,. RSA was increased from plus 30% to plus 350% in 44 tests out of 45 tests following hypertonic (425 mM NaCl) ICA perfusion. RSA was decreased following hypotonic (aqua dest.) ICA perfusion from minus 30% to minus 100% in 37 tests out of 50 tests. The degree of RSA changes was found to depend upon the osmolarity of the solutions. 425mM NaCl and aqua dest. produced greater RSA changes than 290 mM NaCl and 75 mM NaCl. CVS perfusion with isotonic sodium chloride produced a slight increase of RSA compared to control levels (plus 15%). Hypertonic sodium chloride produced a RSA increase from plus 15% to plus 135% in 10 tests out of 14 tests. Hypotonic sodium chloride produced a RSA decrease from minus 15% to minus 80% in 8 tests out of 14 tests. Changes of RSA following ICA perfusions and CVS perfusions were accompanied by changes of BP in the same direction. A quantitative correlation between delta RSA and delta BP could not be found. Results suggest that renal osmoregulatory response to osmotic stimuli in the carotid artery may not just arise in response to changing ADH levels but may also be induced by changes in RSA.

A central osmosensitive receptor for renal sodium excretion

1. The effect on renal Na and water excretion of increasing the NaCl concentration of blood supplying the brain was investigated in conscious water-loaded sheep. Intracarotid infusion ot 4 M-NACl at 0-8 ml./min for 60 min was compared with equivalent intrajugular infusion. 2. A more rapid increase in renal Na excretion and urine osmolality occurred with the intracarotid infusions than with intrajugular infusions. 3. Intracarotid infusions of 2 M sucrose or fructose at 1-6 ml./min for greater increase in renal Na excretion, urine osmolality and a decrease in urine flow rate. 4. The results suggest that there are receptors in the brain sensitive to changes in extracellular tonicity which influence renal Na excretion. It is possible that changes in ADH secretion alone mediate the early natriuresis seen with intracarotid hypertonic infusions although an alternative concurrent mechanism cannot be ruled out.