Age-related declines in thirst and salt appetite responses in male Fischer 344×Brown Norway rats

[Features of water-electrolyte balance in persons of the older age group]

Age-related changes have a great influence on the regulation of water and electrolyte homeostasis in the body, which is regulated by a complex interaction of environmental factors, drinking behavior, the secretion of a number of hormones and hormone-like substances, as well as the innervation and functional state of the kidneys. It is well known that the changes that are part of physiological aging underlie fluid and electrolyte imbalances, exacerbated by the presence of age-related diseases, medications, or a number of external factors such as malnutrition, fluid intake, and the presence of dementia. This review considers literature data on the effect of normal aging on the development of pathology of the water-sodium balance, including dehydration of senile patients, hyponatremia, hypernatremia, changes in the secretion of antidiuretic hormone and the activity of elements of the renin-angiotensin-aldosterone system.

Sex- and age-dependent differences in the hormone and drinking responses to water deprivation

Maintenance of the volume and osmolality of body fluids is important, and the adaptive responses recruited to protect against osmotic stress are crucial for survival. The objective of this work was to compare the responses that occur in aging male and female rats during water deprivation. For this purpose, groups of male and female Wistar rats aged 3 mo (adults) or 18 mo (old) were submitted to water deprivation (WD) for 48 h. The water and sodium (0.15 M NaCl) intake, plasma concentrations of oxytocin (OT), arginine vasopressin (AVP), corticosterone (CORT), atrial natriuretic peptide (ANP), and angiotensin II (ANG II) were determined in hydrated and water-deprived animals. In response to WD, old male and female rats drank less water and saline than adults, and both adult and old females drank more water and saline than respective males. Dehydrated old animals displayed lower ANG II plasma concentration and CORT response compared with the respective normohydrated rats. Dehydrated adult males had higher plasma ANP and AVP as well as lower CORT concentrations than dehydrated adult females. Moreover, plasma OT and CORT levels of old female rats were higher than those in the dehydrated old male rats. Relative expression of ANG II type 1 receptor mRNA was decreased in the subfornical organ of adult and old male rats as well as adult female rats in response to WD. In conclusion, the study elucidated the effect of sex and age on responses induced by WD, altering the degree of dehydration induced by 48 h of WD.

Aging affects isoproterenol-induced water drinking, astrocyte density, and central neuronal activation in female Brown Norway rats

Age-dependent impairments in the central control of compensatory responses to body fluid challenges have received scant experimental attention, especially in females. In the present study, we found that water drinking in response to β-adrenergic activation with isoproterenol (30 μg/kg, s.c.) was reduced by more than half in aged (25 mo) vs. young (5 mo) ovariectomized female Brown Norway rats. To determine whether this age-related decrease in water intake was accompanied by changes in central nervous system areas associated with fluid balance, we assessed astrocyte density and neuronal activation in the SFO, OVLT, SON, AP and NTS of these rats using immunohistochemical labeling for GFAP and c-fos, respectively. GFAP labeling intensity was increased in the SFO, AP, and NTS of aged females independent of treatment, and was increased in the OVLT of isoproterenol-treated rats independent of age. Fos immunolabeling in response to isoproterenol was reduced in both the SFO and the OVLT of aged females compared to young females, but was increased in the SON of female rats of both ages. Finally, fos labeling in the AP and caudal NTS of aged rats was elevated after vehicle control treatment and did not increase in response to isoproterenol as it did in young females. Thus, age-related declines in water drinking are accompanied by site-specific, age-related changes in astrocyte density and neuronal activation. We suggest that astrocyte density may alter the detection and/or processing of signals related to isoproterenol treatment, and thereby alter neuronal activation in areas associated with fluid balance.

Characteristics of and risk factors for death in elderly patients with acute kidney injury: a multicentre retrospective study in China

Purpose of the study

The incidence of acute kidney injury (AKI) with a poor prognosis in the elderly has been increasing each year. This study aimed to investigate the clinical characteristics of and risk factors for death from AKI in the elderly and help improve prognosis.

Study design

This study was a retrospective cohort study based on data from adult patients (≥18 years old) admitted to 15 hospitals in China between 1 January 2009 and 31 December 2011. The characteristics of AKI in the elderly were compared with those in younger patients.

Results

In elderly patients with AKI, rates of hypertension, cardiovascular disease and multiple organ dysfunction syndrome (MODS) were higher than in younger patients (44.2% vs 31.2%, 16.1% vs 4.6% and 20.9% vs 16.9%, respectively), the length of ICU stay was longer (3.8 days vs 2.7 days, P=0.019) and renal biopsy (1.0% vs 7.13%, P<0.001) and dialysis (9.6% vs 19.2%, P<0.001) were performed less. Hospital-acquired (HA) AKI was more common than community-acquired (CA) AKI (60.3% vs 39.7%), while the most common cause of AKI was pre-renal (53.5%). Multiple logistic regression analysis showed that age (OR 1.041, 95% CI 1.023 to 1.059), cardiovascular disease (OR 1.980, 95% CI 1.402 to 2.797), cancer (OR 2.302, 95% CI 1.654 to 3.203), MODS (OR 3.023, 95% CI 1.627 to 5.620) and mechanical ventilation (OR 2.408, 95% CI 1.187 to 4.887) were significant risk factors for death.

Conclusions

HA-AKI and pre-renal AKI were more common in the elderly. Age, cardiovascular disease, cancer, MODS and mechanical ventilation were independent risk factors for death in the elderly with AKI.

Subacute pyridostigmine exposure increases heart rate recovery and cardiac parasympathetic tone in rats

Heart rate recovery (HRR) describes the rapid deceleration of heart rate after strenuous exercise and is an indicator of parasympathetic tone. A reduction in parasympathetic tone occurs in patients with congestive heart failure, resulting in prolonged HRR. Acetylcholinesterase inhibitors, such as pyridostigmine, can enhance parasympathetic tone by increasing cholinergic input to the heart. The objective of this study was to develop a rodent model of HRR to test the hypothesis that subacute pyridostigmine administration decreases cholinesterase activity and accelerates HRR in rats. Ten days after implantation of radiotelemetry transmitters, male Sprague Dawley rats were randomized to control (CTL) or treated (PYR; 0.14 mg/mL pyridostigmine in the drinking water, 29 days) groups. Rats were exercised on a treadmill to record HRR, and blood samples were collected on days 0, 7, 14, and 28 of pyridostigmine administration. Total cholinesterase and acetylcholinesterase (AChE) activity in plasma was decreased by 32%-43% and 57%-80%, respectively, in PYR rats on days 7-28, while plasma butyrylcholinesterase activity did not significantly change. AChE activity in red blood cells was markedly reduced by 64%-66%. HRR recorded 1 minute after exercise was higher in the PYR group on days 7, 14 and 28, and on day 7 when HRR was estimated at 3 and 5 minutes. Autonomic tone was evaluated pharmacologically using sequential administration of muscarinic (atropine) and adrenergic (propranolol) blockers. Parasympathetic tone was increased in PYR rats as compared with the CTL group. These data support the study hypothesis that subacute pyridostigmine administration enhances HRR by increasing cardiac parasympathetic tone.

The characteristics and mortality risk factors for acute kidney injury in different age groups in China-a cross sectional study

AIM

Age is an independent risk factor for acute kidney injury (AKI). The causes and outcomes of AKI in children, middle-aged, and older patients are different. The objective of this country-based study was to identify the characteristics and mortality factors for AKI in different age groups in China.

METHODS

Using data from 374,286 adult patients (≥18 years) admitted to 44 study hospitals, we investigated the characteristics and mortality risk factors for AKI in four different age groups: 18-39 years of age, 40-59 years of age, 60-79 years of age, and ≥80 years of age. The identification criteria for AKI included the 2012 KDIGO AKI definition and an expanded criterion.

RESULTS

The country-based survey included 7604 AKI patients (7604/374,286, 2.03%). The proportions of AKI in the four age groups were 11.52%, 30.79%, 41.03%, and 16.66%, respectively. In any age group, the patients with AKI stage 1 were the majority (43.4%, 42.4%, 46.4%, and 52.2%, respectively), and the most common classification of AKI was pre-renal AKI (44.3%, 51.3%, 52.3%, and 56.4%, respectively). The higher AKI peak stage occurred for the in-hospital mortality factors for AKI in all age groups; except for the AKI stage 2 patients in the 18-39 age group.

CONCLUSION

The characteristics and mortality factors for AKI vary by age in China. Elderly patients were the primary population with AKI, and the most common type of AKI was pre-renal AKI. Special caution should be taken to the old population in hospitalized patients to prevent the pre-renal AKI.

Age-related changes in thirst, salt appetite, and arterial blood pressure in response to aldosterone-dexamethasone combination in rats

This work examined the effects of age on daily water and sodium ingestion and cardiovascular responses to chronic administration of the mineralocorticoid, aldosterone (ALDO) either alone or together with the glucocorticoid, dexamethasone (DEX). Young (4 mo), adult (12 mo), and aged (30 mo) male Brown Norway rats were prepared for continuous telemetry recording of blood pressure (BP) and heart rate (HR). Baseline water and sodium (i.e., 0.3 M NaCl) intake, BP, and HR were established for 10 days. Then ALDO (60 μg/day sc) was infused alone, or together with DEX (2.5 or 20 μg/day sc), for another 10 days. Compared with baseline levels, ALDO stimulated comparable increases in daily saline intake at all ages. ALDO together with the higher dose of DEX (i.e., ALDO/DEX20) increased daily saline intake more than did ALDO, but less so in aged rats. Infusion of ALDO/DEX20 increased mean arterial pressure (MAP), and decreased HR, more than did infusion of ALDO. The changes in MAP in response to both treatments depended on age. For all ages, MAP and saline intake increased simultaneously during ALDO, while MAP always increased before saline intake did during ALDO/DEX20. Contrary to our predictions, MAP did not increase more in old rats in response to either treatment. We speculate that age-related declines in cardiovascular responses to glucocorticoids contributed to the attenuated increases in sodium intake in response to glucocorticoids that were observed in older animals.

Salt appetite in the elderly

The present study investigated whether salt appetite in the elderly is impaired similar to thirst because of the commonality of their physiological substrates and whether alterations in salt appetite are related to mood. Elderly (65–85 years, n 30) and middle-aged (45–58 years, n 30) men and women were compared in two test sessions. Thirst, psychophysical ratings of taste solutions, dietary Na and energy intakes, seasoning with salt and sugar, number of salty and sweet snacks consumed, preferred amounts of salt in soup and sugar in tea, and an overall measure of salt appetite and its relationship with mood, nocturia and sleep were measured. Elderly participants were found to be less thirsty and respond less to thirst. In contrast, no impairment of salt appetite was found in them, and although they had a reduced dietary Na intake, it dissipated when corrected for their reduced dietary energy intake. Diet composition and Na intake were found to be similar in middle-aged and elderly participants, despite the lesser intake in elderly participants. There were no age-related differences in the intensity of taste or hedonic profile of Na, in salting habits, in tests of salting soup, or number of salty snacks consumed. No relationship of any measure of salt appetite with mood measured by the Positive and Negative Affect Schedule, frequency of nocturia, or sleep duration was observed. The age-related impairment of the physiology of mineralofluid regulation, while compromising thirst and fluid intake, spares salt appetite, suggesting that salt appetite in humans is not regulated physiologically. Intact salt appetite in the elderly might be utilised judiciously to prevent hyponatraemia, increase thirst and improve appetite.