Low sodium haemodialysis reduces interdialytic fluid consumption but paradoxically increases post-dialysis thirst

Background Interdialytic weight gain (IDWG) can be reduced by lowering the dialysate sodium concentration ([Na]) in haemodialysis patients. It has been assumed that this is because thirst is reduced, although this has been difficult to prove. We compared thirst patterns in stable haemodialysis patients with high and low IDWG using a novel technique and compared the effect of low sodium dialysis (LSD) with normal sodium dialysis (NSD). Methods Eight patients with initial high IDWG and seven with low IDWG completed hourly visual analogue ratings of thirst using a modified palmtop computer during the dialysis day and the interdialytic day. The dialysate [Na] was progressively reduced by up to 5 mmol/l over five treatments. Dialysis continued at the lowest attained [Na] for 2 weeks and the measurements were repeated. The dialysate [Na] then returned to baseline and the process was repeated. Results Baseline interdialytic day mean thirst was higher than the dialysis day mean for the high IDWG group (49.9±14.0 vs 36.2±16.6) and higher than the low weight gain group (49.9±14.0 vs 34.1±14.6). This trend persisted on LSD, but there was a pronounced increase in post-dialysis thirst scores for both groups (high IDWG: 46±13 vs 30±21; low IDWG: 48±24 vs 33±18). The high IDWG group demonstrated lower IDWG during LSD than NSD (2.23±0.98 vs 2.86±0.38 kg; P<0.05). Conclusions Our results indicate that patients with high IDWG experience more intense feelings of thirst on the interdialytic day. LSD reduces their IDWG, but paradoxically increases thirst in the immediate post-dialysis period.

Effect of acupressure on thirst in hemodialysis patients

Background: Thirst and dry mouth are common among hemodialysis (HD) patients. This paper reports a study to evaluate the impact of an acupressure program on HD patients’ thirst and salivary flow rates. Methods: The acupressure program included placebo, followed by true acupressure each applied for 4 weeks. Twenty-eight patients (mean age 57.6, SD = 16.13 years) first received a sticker as placebo acupressure at two acupoints CV23 and TE17 three times a week for 4 weeks, and then received true acupressure in the same area for the next 4 weeks. Salivary flow rate and thirst intensity were measured at baseline, during and after treatment completion for both the placebo and true acupressure program. Results: The true acupressure program was associated with significantly increased salivary flow rate (0.09 ± 0.08 ml/min at baseline to 0.12 ± 0.08 ml/min after treatments completion, p = 0.04). The mean thirst intensity also improved from 4.21 ± 2.66 at baseline to 2.43 ± 2.32 (p = 0.008) after treatment completion in HD patients. There was no statistically significant difference in pre-post program salivary flow rate; however, significant improvement in thirst intensity scores was observed (p = 0.009) in the placebo acupressure program. Conclusion: This study provides preliminary evidence that acupressure may be effective in improving salivary flow rates and thirst intensity.

Thirst for knowledge: the effects of curiosity and interest on memory in younger and older adults

Given age-related memory impairments, one’s level of curiosity or interest could enhance memory for certain information. In the current study, younger and older adults read trivia questions, rated how curious they were to learn each answer, provided confidence and interest ratings, and judgments of learning (JOL) after learning the answer. No age-related differences in memory were found. Analyses indicated that curiosity and interest contributed to the formation of JOLs. Additionally, interest had a unique increasing relationship with older, but not younger, adults’ memory performance after a week. The results suggest that subjective interest may serve to enhance older adults’ memory.

Osmoregulatory fluid intake but not hypovolemic thirst is intact in mice lacking angiotensin

Water intakes in response to hypertonic, hypovolemic, and dehydrational stimuli were investigated in mice lacking angiotensin II as a result of deletion of the angiotensinogen gene (Agt-/- mice), and in C57BL6 wild-type (WT) mice. Baseline daily water intake in Agt-/- mice was approximately threefold that of WT mice because of a renal developmental disorder of the urinary concentrating mechanisms in Agt-/- mice. Intraperitoneal injection of hypertonic saline (0.4 and 0.8 mol/l NaCl) caused a similar dose-dependent increase in water intake in both Agt-/- and WT mice during the hour following injection. As well, Agt-/- mice drank appropriate volumes of water following water deprivation for 7 h. However, Agt-/- mice did not increase water or 0.3 mol/l NaCl intake in the 8 h following administration of a hypovolemic stimulus (30% polyethylene glycol sc), whereas WT mice increased intakes of both solutions during this time. Osmoregulatory regions of the brain [hypothalamic paraventricular and supraoptic nuclei, median preoptic nucleus, organum vasculosum of the lamina terminalis (OVLT), and subfornical organ] showed an increased number of neurons exhibiting Fos-immunoreactivity in response to intraperitoneal hypertonic NaCl in both Agt-/- mice and WT mice. Polyethylene glycol treatment increased Fos-immunoreactivity in the subfornical organ, OVLT, and supraoptic nuclei in WT mice but only increased Fos-immunoreactivity in the supraoptic nucleus in Agt-/- mice. These data show that brain angiotensin is not essential for the adequate functioning of neural pathways mediating osmoregulatory thirst. However, angiotensin II of either peripheral or central origin is probably necessary for thirst and salt appetite that results from hypovolemia

Vasopressin and angiotensin receptors of the medial septal area of the brain in the control of thirst and salt appetite induced by vasopressin in water-deprived and sodium-depleted rats

In this study we investigated the influence of d(CH2)(5)-Tyr (Me)-AVP (A(1) AVP) and [Adamanteanacatyl(1),D-ET-D-Tyr(2), Va1(4), aminobutyril(6) ,As-8,As-9]-AVP 9 (A(2)AVP), antagonists of V-1 and V-2 arginine(8)-vasopressin (AVP) receptors, respectively, as well as the effects of losartan and CGP42112A, antagonists of angiotensin II (ANGII) AT(1) and AT(2), receptors, respectively, on water and 0.3 M sodium intake induced by water deprivation or sodium depletion (furosemide treatment) and enhanced by AVP injected into the medial septal area (N4SA). A stainless steel carmulawas implanted into the medial septal area (NISA) of male Holtzman rats AVP injection enhanced water and sodium intake in a dose-dependent manner. Pretreatment with V-1 antagonist injected into the MSA produced a dose-dependent reduction, whereas prior injection of V-2 antagonist increased, in a dose-dependent manner, the water and sodium responses elicited by the administration of AVP. Both AT(1) and AT(2) antagonists administered into the MSA elicited a concentration-dependent decrease in water and sodium intake induced by AVP, while simultaneous injection of the two antagonists was more effective in decreasing AVP responses. These results also indicate that the increase in water and sodium intake induced by AvT was mediated primarily by MSA AT(1) receptors. (c) 2007 Published by Elsevier B.V.

Water deprivation and the double- depletion hypothesis: common neural mechanisms underlie thirst and salt appetite

Water deprivation-induced thirst is explained by the double-depletion hypothesis, which predicts that dehydration of the two major body fluid compartments, the extracellular and intracellular compartments, activates signals that combine centrally to induce water intake. However, sodium appetite is also elicited by water deprivation. In this brief review, we stress the importance of the water-depletion and partial extracellular fluid-repletion protocol which permits the distinction between sodium appetite and thirst. Consistent enhancement or a de novo production of sodium intake induced by deactivation of inhibitory nuclei (e.g., lateral parabrachial nucleus) or hormones (oxytocin, atrial natriuretic peptide), in water-deprived, extracellular-dehydrated or, contrary to tradition, intracellular-dehydrated rats, suggests that sodium appetite and thirst share more mechanisms than previously thought. Water deprivation has physiological and health effects in humans that might be related to the salt craving shown by our species.

INJECTION OF RAMIPRIL INTO THE LATERAL VENTRICLE INTERFERES WITH THE DRINKING RESPONSE INDUCED BY PHARMACOLOGICAL AND NATURAL THIRST STIMULI

We investigated the effects of ramipril, an angiotensin I-converting enzyme (ACE) inhibitor, on water intake by male Holtzman rats (250-300 g) with cannulae implanted into the lateral ventricle. Intracerebroventricular (icv) injection of ramipril (1 mu g/mu l) significantly reduced drinking in response to subcutaneous (sc) injection of isoprenaline (100 mu g/kg) from 8.49 +/- 0.69 to 2.96 +/- 0.36 ml/2 h, polyethyleneglycol (PEG) (30% w/v, 10 ml/kg) from 9.51 +/- 2.20 to 1.6 +/- 0.34 ml/2 h or water deprivation for 24 h from 12.61 +/- 0.83 to 5.10 +/- 1.37 ml/2 h. Ramipril had no effect on water intake induced by cellular dehydration produced by sc injection of hypertonic saline (2 M NaCl). These results are consistent with the hypothesis that ramipril acts as an ACE-blocking agent in the brain. The possibility that ramipril is transformed to ramiprilat, the active drug, by the brain is suggested.

CENTRAL ANGIOTENSIN-CONVERTING ENZYME-BLOCKADE AND THIRST

1. The effect of lisinopril, a potent inhibitor of angiotensin converting enzyme (ACE), injected into the medial preoptic area (MPOA) on water intake was investigated in male Holtzman rats (200-250 g).2. Injection of lisinopril (2 mug/mul) into the MPOA abolished the water intake induced by subcutaneous (sc) injection of isoprenaline (100%) and water deprivation (90%) and drastically reduced the water intake induced by sc injection of polyethyleneglycol (60%). A small reduction of water intake induced by lisinopril was also observed 90 and 120 min after sc hypertonic saline (N = 10 for each group).3. These results suggest that central ACE activation, particularly in the MPOA, plays an important role in the dipsogenic responses induced by the agents studied.

The lateral preoptic area plays a dual role in the regulation of thirst in the rat

Electrolyte lesion and ibotenic acid lesion of the lateral preoptic area (LPO) of the rat were used to study the participation of this area in drinking behavior. Drinking was induced by cellular dehydration, hypovolemia, hypotension, and water deprivation. The animals with electrolytic lesion of the LPO showed a significant reduction in water intake in response to cellular dehydration, hypotension, and deprivation. The animals with ibotenic acid lesion of the LPO increased the water consumption produced by subcutaneous (SC) injection of hypertonic saline. The amount of water intake after SC injection of polyethyleneglycol (PEG) or isoprenaline was similar in control and ibotenic acid-lesioned animals. The rats with ibotenic acid lesion of the LPO drank significantly more water than control animals. Fibers of passage may also influence the drinking response, and the LPO may have osmosensitive receptors that facilitate water intake in connection with other areas of the central nervous system (CNS) that are implicated in drinking behavior.

Cholecystokinin actions in the parabrachial nucleus: effects on thirst and salt appetite

The present study investigated the effects of bilateral injections of the nonselective CCK receptor antagonist proglumide or CCK-8 into the lateral parabrachial nuclei (LPBN) on the ingestion of 0.3 M NaCl and water induced by intracerebroventricular injection of ANG II or by a combined treatment with subcutaneous furosemide (Furo) + captopril (Cap). Compared with the injection of saline (vehicle), bilateral LPBN injections of proglumide (50 mu g . 200 nl(-1). site(-1)) increased the intake of 0.3 ill NaCl induced by intracerebroventricular ANG II (50 ng/1 mu l). Bilateral injections of proglumide into the LPBN also increased ANG II-induced water intake when NaCl was simultaneously available, but not when only water was present. Similarly, the ingestion of 0.3 M NaCl and water induced by the treatment with Furo (10 mg/kg) + Cap (5 mg/kg) was increased by bilateral LPBN proglumide pretreatment. Bilateral CCK-8 (0.5 mu g . 200 nl(-1). site(-1)) injections into the LPBN did not change Furo + Cap-induced 0.3 M NaCl intake but reduced water consumption. When only water was available after intracerebroventricular ANG II, bilateral LPBN injections of proglumide or CCK-8 had no effect or significantly reduced water intake compared with LPBN vehicle-treated rats. Taken together, these results suggest that CCK actions in the LPBN play a modulatory role on the control of NaCl and water intake induced by experimental treatments that induce hypovolemia and/or hypotension or that mimic those states.