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Age-associated alterations in thirst and arginine vasopressin in response to a water or sodium load.

We have examined simultaneous changes in thirst, plasma osmolality and arginine vasopressin, after oral water loading or hypertonic saline infusion. The studies were carried out in the same subjects, comprising young controls aged 26.8 years (SD 4.8, n = 10) and health status-defined elderly people aged 72.1 years (SD 3.1, n = 10). Water loading caused significant falls in plasma osmolality (p < 0.001) and thirst (p < 0.001), but there was no variation with age. Infusion with 462 mmol/l of sodium chloride increased plasma osmolality significantly (p < 0.001), but there was no variation with age (p = 0.12). The perception of thirst during the osmotic loading experiment was recorded differently by the two age groups (p < 0.0001). However, linear regression analysis showed no age difference in the relationship between thirst and plasma osmolality during osmotic loading. During osmotic loading the relationship between the plasma concentration of arginine vasopressin in response to increasing plasma osmolality varied significantly (slope: p = 0.02; intercept: p = 0.02). Plasma arginine vasopressin rose more rapidly with increasing plasma osmolality in old subjects.

Adult↗

Osmoregulation of thirst and vasopressin secretion in Kallmann's syndrome.

It has been suggested that abnormalities of thirst and vasopressin secretion commonly coexist with Kallmann's syndrome. Out-patient plasma osmolality, plasma sodium and 24-hour urine volume were similar in 10 patients with Kallmann's syndrome and 10 matched controls. Six patients underwent dynamic testing of osmoregulation with hypertonic sodium chloride infusion. There were similar rises in plasma AVP concentration in patients (0.4 +/- 0.1-6.2 +/- 1.2 pmol/l, P less than 0.001) and controls (0.4 +/- 0.1-5.7 +/- 1.0 pmol/l P less than 0.001). Thirst ratings rose in similar fashion in patients (0.7 +/- 0.3-6.2 +/- 1.0 cm, P less than 0.001) and controls (1.0 +/- 0.3-7.2 +/- 0.5 cm. P less than 0.001). Drinking rapidly abolished thirst and lowered AVP concentrations in both groups before major changes in plasma osmolality occurred. Linear regression analysis defined similar osmotic thresholds for thirst onset and vasopressin release in the two groups, and there was no difference in the calculated sensitivity of the osmoreceptor/vasopressin secretory unit as defined by the slopes of the regression lines. We conclude that osmoregulation is normal in Kallmann's syndrome.

Adolescent↗

Neuroendocrine, fluid balance, and thirst responses to alcohol in alcoholics.

This study simultaneously evaluated multiple circulating neurohormones, osmolality, thirst, and fluid balance in eight actively drinking, alcoholic males and seven controls before and 12 hr after an ethanol challenge. Basal levels of serum osmolality and thirst were significantly higher in alcoholics compared with controls, yet actively drinking alcoholics at the start of the study had normal vasopressin (AVP) levels, plasma angiotensin II (Ang II), plasma renin activity, plasma aldosterone (Aldo), and plasma catecholamines. In response to ethanol, serum osmolalities rose significantly higher while plasma AVP levels became significantly suppressed in alcoholics. After the ethanol stimulus, plasma Ang II levels of alcoholics were significantly higher than those of controls at 11 AM (12.15 +/- 4.49 vs. 1.83 +/- 0.6 pg/ml, p less than 0.02) and 12 noon (14.93 +/- 6.81 vs. 1.37 +/- 0.17 pg/ml, p less than 0.04). Neither plasma renin activity nor Aldo changed in accordance with the elevated plasma Ang II in alcoholics. Diuresis in the alcoholics, assessed by the sum of urine output following the challenge dose, was significantly less than that of controls. Thirst scores and fluid intakes after the ethanol challenge did not differ between alcoholics and controls. The lack of an Ang II-mediated increase in plasma Aldo or thirst response suggests that ethanol may have a specific blunting effect on Ang II receptors. This study demonstrates that ethanol can be used as a provocative test in chronic alcoholics to uncover aberrant hormonal responses for two systems, namely, Ang II and AVP.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

Hypohydration during exercise in children: effect on thirst, drink preferences, and rehydration.

This study examined changes in children's thirst and drink preferences during exercise-induced hypohydration and their spontaneous rehydration during a 30-min recovery. Twenty-four 9- to 13-year-old children (14 females, 10 males) participated in four intermittent 90-min cycling sessions in the heat (35 degrees C, 20% relative humidity); the sessions differed in the drinks the children were sampling (apple, orange, water, and grape). Thirst and drink preferences were assessed (analog and category scales) while children dehydrated up to about 0.76% of their initial body weight. During 90 min dehydration, there was an increase in thirst intensity for all drinks. The grape was the preferable drink throughout the dehydration phase, but its desirability did not increase as much as the desirability of the orange, apple, and water drinks. During the 30-min recovery, most subjects rehydrated spontaneously, exceeding baseline levels by 0.76 +/- 0.15% (M +/- SEM) for grape, 0.40 +/- 0.15 for apple, 0.71 +/- 0.18 for orange, and 0.48 +/- 0.16 for water. Although full rehydration was achieved with all drinks, the magnitude of rehydration was statistically greater with grape and orange than water and apple (p < .05). It was concluded that mild hypohydration during exercise increased children's thirst and drink desirability. In general, spontaneous overshoot of fluid consumption occurred during recovery.

Adolescent↗

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.

Adult↗

Ontogeny of thirst in the infant rat.

The development of water drinking in response to thirst stimuli was found to be precocious and sequential in the neonatal rat. It was studied in suckling rats with a technique that took advantage of their vigorous consummatory reflexes and minimized appetitive responding. Responsiveness to the following thirst challenges appeared in the suckling rat with a clear timetable: cellular dehydration at 2 days of age, hypovolemia induced by colloid dialysis at 4 days, and beta-adrenergic activation at 6 days. Responsiveness to deprivation from mother's milk was vigorous at the earliest day tested (2 days) but could not be distinguished from hunger. Rats weaned, isolated, and tested as miniadults responded appetitively to thirst challenges as early as 16 days of age. But they required a warm environment, optimum access to the water source, and sufficient time to respond. As revealed by consummatory responding, the controls of water drinking mature weeks before they are required. They precede the maturation of capacities for sustained appetitive responding. These appear in the last week of the suckling period, yielding animals that are prepared for adult, thirst-motivated behavior at the onset of weaning.

Animals↗

Elevated dietary salt suppresses renin secretion but not thirst evoked by arterial hypotension in rats.

Increased dietary salt intake was used as a nonpharmacological tool to blunt hypotension-induced increases in plasma renin activity (PRA) in order to evaluate the contribution of the renin-angiotensin system (RAS) to hypotension-induced thirst. Rats were maintained on 8% NaCl (high) or 1% NaCl (standard) diet for at least 2 wk, and then arterial hypotension was produced by administration of the arteriolar vasodilator diazoxide. Despite marked reductions in PRA, rats maintained on the high-salt diet drank similar amounts of water, displayed similar latencies to drink, and had similar degrees of hypotension compared with rats maintained on the standard diet. Furthermore, blockade of ANG II production by an intravenous infusion of the angiotensin-converting enzyme inhibitor captopril attenuated the hypotension-induced water intake similarly in rats fed standard and high-salt diet. Additional experiments showed that increases in dietary salt did not alter thirst stimulated by the acetylcholine agonist carbachol administered into the lateral ventricle; however, increases in dietary salt did enhance thirst evoked by central ANG II. Collectively, the present findings suggest that hypotension-evoked thirst in rats fed a high-salt diet is dependent on the peripheral RAS despite marked reductions in PRA.

Angiotensin II↗

Osmoregulation of thirst and vasopressin during normal menstrual cycle.

Changes in osmoregulation during normal menstrual cycle were examined in 15 healthy women. In 10 women, studied repetitively during two consecutive menstrual cycles, basal plasma osmolality, sodium, and urea decreased by 4 mosmol/kg, 2 meq/l, and 0.5 mM, respectively (all P less than 0.02) from the follicular to luteal phase. Plasma vasopressin, protein, hematocrit, mean arterial pressure, and body weight did not change. In five other women, diluting capacity and osmotic control of thirst and vasopressin release were assessed in follicular, ovulatory, and luteal phases. Responses of thirst and/or plasma vasopressin, urine osmolality, osmolal and free water clearance to water loading, and infusion of hypertonic saline were normal and similar in the three phases. However, the plasma osmolality at which plasma vasopressin and urine osmolality were maximally suppressed as well as calculated osmotic thresholds for thirst and vasopressin release were lower by 5 mosmol/kg in the luteal than in the follicular phase. This lowering of osmotic thresholds for thirst and vasopressin release, which occurs in the luteal phase, is qualitatively similar to that observed in pregnancy and should be taken into account when studying water balance and regulation of vasopressin secretion in healthy cycling women.

Adult↗

Thirst in Brattleboro rats.

Thirst mechanisms in Brattleboro rats are activated because of a deficiency in circulating vasopressin. Plasma osmolality, renin, and angiotensin II (ANG II) are increased. We measured the responsiveness of Brattleboro rats and appropriate control strains to cellular and extracellular thirst stimuli taking the spontaneous base-line water intake into account. Brattleboro rats drank more in response to intraperitoneal hypertonic NaCl than controls, but when their fluid losses were prevented by nephrectomy they did not overdrink. Despite low urinary concentration, Brattleboro rats excreted the sodium load at least as rapidly as the controls. Brattleboro rats drank after intracranial injection of renin, renin substrate, and ANG I and II. The dose-response curves were similar to controls, although the Nottingham Long-Evans control strain drank significantly less in response to some doses of the peptides. Intracranial captopril inhibited renin- and ANG I-induced but not ANG II-induced drinking. Isoproterenol reduced spontaneous drinking of Brattleboro rats but increased drinking in controls. However, when urinary losses were prevented by ureteric ligation, isoproterenol caused markedly greater water intake in Brattleboro rats than in controls. Subcutaneous captopril in moderate, thirst-enhancing doses also caused a larger increase in water intake in Brattleboro rats than in controls. Therefore the renin-angiotensin system of Brattleboro rats is more responsive to renin-dependent thirst challenges than that of normal controls.

Angiotensin I↗

Loss of osmotic thirst in multiple system atrophy: association with sinoaortic baroreceptor deafferentation.

We evaluated plasma osmolality (pOsm), thirst, and vasopressin response to hypertonic saline infusion in 14 patients with multiple system atrophy (MSA). This disease is characterized by the degeneration of noradrenergic neurons in the central nervous system and severe orthostatic hypotension. Seven patients were also characterized by the lack of vasopressin response to hypotension (group B) and seven by a preserved response (group A). In group A pOsm rose from 290 +/- 2 to 312 +/- 6 mosmol/kgH2O, vasopressin from 0.9 +/- 0.3 to 5.7 +/- 0.5 pmol/l, and thirst from 1.1 +/- 0.1 to 8.7 +/- 1.1 cm on the visual analog scale. After saline, patients drank 1,215 +/- 150 ml of water (no different from healthy controls). In group B patients' pOsm rose from 296 +/- 3 to 325 +/- 6 mosmol/kgH2O and vasopressin from 1.2 +/- 0.1 to 19.6 +/- 0.4 pmol/l (P < 0.01 vs. group A and controls). Group B patients had no thirst during saline and drank little after the challenge (175 +/- 50 ml; P < 0.01 vs. group A and control). Forced drinking decreased vasopressin in patients before changes in pOsm, showing that inhibitory afferents from oropharyngeal mucosa were intact. In MSA patients with altered afferent control of vasopressin there is a dissociation between the osmotic control of thirst and the osmotic control of vasopressin.

Afferent Pathways↗

Thirst and fluid regulatory responses to hypertonicity in older adults.

To assess the fluid regulatory responses in aging adults, we measured thirst perception and osmoregulation during and after infusion of hypertonic NaCl) saline in older (72 +/- 2 yr, n = 6) and younger (26 +/- n = 6) subjects. Hypertonic saline was infused at 0.1 min-1.kg-1 for 120 min. On a separate day, the same subjects were infused identically with isotonic saline as a control. After infusion and a 30-min equilibration period, the drank water ad libitum for 180 min. Hypertonic infusion led to graded increases in plasma osmolality (Posm; 18 +/- 2 and 20 +/- 2 mosmol/kgH2O) and percent changes plasma volume (16.2 +/- 1.9 and 18.0 +/- 1.2%) that were in older and younger subjects. Osmotically stimulated increases in thirst (94.8 +/- 18.9 and 88.3 +/- 25.6 mm), assessed on a line rating scale, and plasma arginine vasopressin concentration (6.08 +/- 1.50 and 4.51 +/- 1.37 pg/ml, for older younger, respectively) were also unaffected by age. subsequent hypervolemia, both groups of subjects sufficient water to restore preinfusion levels of Posm. Renal handling of free water and sodium was also unaffected by age during recovery from hypertonic saline infusion, but was significantly lower in older subjects during recovery from saline infusion, resulting in net fluid retention and a significant fall in Posm (6 mosmol/kgH2O). In contrast to earlier reports of a blunted thirst response to dehydration hypertonicity, we found that osmotically stimulated thirst and renal osmoregulation were intact in older adults after hypertonic saline infusion.

Adult↗

Role of brain angiotensin II in thirst and sodium appetite of sheep.

The contribution of brain angiotensin II (ANG II) to thirst and Na+ appetite of sheep was evaluated. Thirst was stimulated by water deprivation, intracarotid or intracerebroventricular infusion of ANG II, or intracarotid or intracerebroventricular infusion of hypertonic solution. Intracerebroventricular infusion, over 1-3 h, of the ANG II type 1 (AT1) receptor antagonist, losartan, decreased or abolished water intake caused by all of the stimuli tested. Intracerebroventricular infusion of ZD-7155, another AT1-receptor antagonist, blocked ANG II-induced water intake. Neither losartan nor ZD-7155 infused intracerebroventricularly altered the Na+ appetite of Na(+)-depleted sheep. Intracerebroventricular infusion of losartan over 3 h, however, did block the increase in water intake and the decrease in Na+ intake caused by intracerebroventricular infusion of hypertonic NaCl in Na(+)-depleted sheep. Intracerebroventricular infusion of the ANG II type 2 (AT2) receptor antagonist, PD-123319, over 1-3 h, did not alter ANG II-induced water intake or Na+ depletion-induced Na+ intake. These results are consistent with the proposition that brain ANG II, working via AT1 receptors, is involved in the neural system controlling some aspects of physiological thirst and Na+ appetite. A role for AT2 receptors in physiological thirst or Na+ appetite is not supported by the present results.

Analysis of Variance↗

Effect of hyperosmotic solutions on salt excretion and thirst in rats.

We investigated urinary changes and thirst induced by infusion of hyperosmotic solutions in freely moving rats. Intracarotid infusions of 0.3 M NaCl (4 ml/20 min, split between both internal carotid arteries) caused a larger increase in excretion of Na(+) and K(+) than intravenous infusions, indicating that cephalic sensors were involved in the response to intracarotid infusions. Intravenous and intracarotid infusions of hyperosmotic glycerol or urea (300 mM in 150 mM NaCl) had little or no effect, suggesting the sensors were outside the blood-brain barrier (BBB). Intracarotid infusion of hypertonic mannitol (300 mM in 150 mM NaCl) was more effective than intravenous infusion, suggesting that cell volume rather than Na(+) concentration of the blood was critical. Similarly, intracarotid infusion (2 ml/20 min, split between both sides), but not intravenous infusion of hypertonic NaCl or mannitol caused thirst. Hyperosmotic glycerol, infused intravenously or into the carotid arteries, did not cause thirst. We conclude that both thirst and electrolyte excretion depend on a cell volume sensor that is located in the head, but outside the BBB.

Animals↗

Angiotensin, thirst, and sodium appetite: retrospect and prospect.

The fact that drinking in response to some hypovolemic stimuli was attenuated by nephrectomy but not by ureteric ligation led to the suggestion that the renal renin-angiotensin system may play a role in hypovolemic thirst. The isolation of a thirst factor from the kidney and the demonstration that this substance was renin supported the hypothesis. Subsequently, it was shown that the effects of renin on drinking were mediated through angiotensin II, which proved to be a potent dipsogenic substance when administered systemically or injected directly into the brain. Recently, it has been shown that angiotensin II, infused intravenously or through the carotid artery at rates that produce increases in plasma angiotensin II levels similar to those that occur in mild sodium depletion, causes the water-replete animal to drink. This discovery establishes that angiotensin is a physiological stimulus to drinking but it leaves open the question of the extent of the involvement of renal renin in normal thirst. Other unsolved problems are the role of cerebral isorenin in angiotensin thirst and its relationship with renal renin, and in view of its stimulating action on sodium intake when infused into the brain, whether angiotensin plays a significant role in sodium appetite.

Angiotensins↗

The effect of acute administration of an angiotensin converting enzyme inhibitor, captopril (SQ 14,225), on experimentally induced thirsts in rats.

In order to assess the role of angiotensin in the genesis of certain types of thirst, rats were administered the angiotensin converting enzyme inhibitor, captopril, in an attempt to block the increased water intake induced either by water deprivation or by i.p. administration of hypertonic saline. Water deprivation for 24 hr resulted in an increased water intake. Acute administration of 50 mg of captopril per kg i.p. at 45 or 60, but not at 15 or 30, min before return of water to the dehydrated rats significantly attenuated the drinking response. Rats administered 1% b.wt. i.p. of 0.25, 0.50, 0.75 or 1.00 M NaCl solution increased proportionately their water intake. Acute administration of 35 mg of captopril per kg b. wt. i.p. 15 min before loading with NaCl solution at any of the above concentrations had no effect on the increased thirst induced. These findings suggest that hypertonic saline-induced thirst is not mediated by angiotensin II receptors while water deprivation-induced thirst may involve both osmoreceptors and angiotensin II receptors.

Angiotensin-Converting Enzyme Inhibitors↗

[Lack of interference by carbamylcholine on the renin-angiotensin system thirst mechanism].

The thirst mechanism by carbamylcholine and the possible interactions with the renin-angiotensin system have been investigated. Rats placed in metabolic cages in order to measure the drunk water and the emitted urine were used. Carbamylcholine has been injected together with captopril, an inhibitor of the enzyme converting angiotensin I into angiotensin II, and with propranolol, which blocks the renin beta-receptors respectively. When given in combination with these substances, the thirst by carbamylcholine was not reduced; this result does not favour the hypothesis of a role of the renin-angiotensin system. On the contrary, the thirst by carbamylcholine seems to be due to a vasomotor action. These results confirm the hypothesis that an unbalance between the blood circulating mass and the venous vessels underlies the regulation of the thirst.

Angiotensin II↗

Effect of atrial natriuretic hormone on vasopressin and thirst response to osmotic stimulation in human subjects.

To evaluate the effect of systemically administered atrial natriuretic hormone (ANH) on osmotically induced secretion of arginine vasopressin (AVP) and thirst sensation, 11 healthy men, aged 18 to 28 years, were studied on four occasions. The intravenous infusions of placebo (P) or one of three doses of ser-tyr28 human ANH (0.6 [LD], 1.8 [MD], and 5.4 [HD] pmol/kg/min) were given in random order over 2 hours. During the second hour, subjects also received a 5% saline (HS) infusion (0.1 ml/kg/min). The baseline parameters were similar on each of the study days. Plasma ANH levels increased approximately twofold, eightfold, and 25-fold during LD, MD, and HD infusions, respectively. HS infusion caused increases in serum sodium level (5 to 7 mEq/L) and osmolality (14 to 15 mOsm/L) (p < 0.001). During HS infusion on P day, ANH levels almost doubled (p < 0.001). AVP levels remained stable during the first hour of ANH infusions. An addition of HS caused a significant increase in AVP levels (p < 0.001). The magnitude of this increase was similar on each of the study days. Similarly, thirst perception increased significantly (p < 0.01) and to the same extent during HS infusion on all study days. Both AVP levels and thirst showed a very good correlation with serum osmolality on each of the study days, and there were no significant differences between any of the slopes or intercepts. We conclude that short-term elevation of plasma ANH levels up to 25-fold affects neither the osmotically stimulated secretion of AVP nor thirst perception.

Adult↗

Asymmetrical interactions between thirst and hunger in Pavlovian-instrumental transfer.

Pavlovian-instrumental transfer experiments have demonstrated that a stimulus paired with a sucrose solution under hunger will increase instrumental performance under thirst relative to a stimulus previously paired with food pellets. In Experiment 1 it was demonstrated that this difference is, in part, produced by suppression induced by the pellet stimulus, which, it was found, acted to reduce instrumental performance under thirst. In Experiment 2, the reverse shift was examined, comparing the effects of stimuli paired with either a saline solution or a sucrose solution under thirst on instrumental performance under hunger. Although the sucrose stimulus was found to elevate performance when hungry, the saline stimulus was found to be without effect. This asymmetry in the interaction between hunger and thirst is discussed in terms of the way motivational states control the interaction between sensory and affective components of the reinforcer.

Animals↗