Physiological and Biochemical Indices of Neurohypophyseal Function in the Aging Fischer Rat

Silverman, William F.; Aravich, Paul A.; Sladek, John R.; Sladek, Celia D.

doi:10.1159/000125571

Cited by 26 publications

(19 citation statements)

References 33 publications

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“…This may be an artifact reflecting stress reactions by the old rats to the novel laboratory situation. Others have noted highly variable responses in old rats before significant handling (34). Differences in ad libitum intakes between young and old rats seem to depend on strain and whether intakes are adjusted for body weight.…”

Section: Discussionmentioning

confidence: 95%

Thirst and salt appetite responses in young and old Brown Norway rats

Thunhorst

Johnson²

2003

American Journal of Physiology-Regulatory, Integrative and Comp

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Thunhorst, Robert L., and Alan Kim Johnson. Thirst and salt appetite responses in young and old Brown Norway rats. Am J Physiol Regul Integr Comp Physiol 284: R317-R327, 2003. First published October 10, 2002 10.1152/ ajpregu.00368.2002 Norway rats aged 4 mo (young) and 20 mo (old) received a series of experimental challenges to body fluid homeostasis over ϳ3 mo. Water was available for drinking in some tests, and both water and 0.3 M NaCl were available in others. The series included three episodes of extracellular fluid depletion (i.e., furosemide ϩ 20 h of sodium restriction), two tests involving intracellular fluid depletion (i.e., hypertonic saline: 1 or 2 M NaCl at 2 ml/kg body wt sc), one test involving overnight food and fluid restriction, and testing with captopril adulteration of the drinking water (0.1 mg/ml) for several days. Old rats were significantly heavier than young rats throughout testing. Old rats drank less water and 0.3 M NaCl after sodium deprivation than young rats, in terms of absolute and body weightadjusted intakes. Old rats drank only half as much water as young rats in response to subcutaneous hypertonic NaCl when intakes were adjusted for body weight. Old rats drank less 0.3 M NaCl than young rats after overnight food and fluid restriction when intakes were adjusted for body weight. In response to captopril adulteration of the drinking water, young rats significantly increased daily ingestion of 0.3 M NaCl when it was available as an alternative to water and significantly increased daily water intakes when only water was available, in terms of absolute and body weight-adjusted intakes. Old rats had no response to captopril treatment. These results add important new information to previous reports that aging rats have diminished thirst and nearabsent salt appetite responses to regulatory challenges. aging; drinking; diuresis; natriuresis; dehydration; hypovolemia ELDERLY HUMANS CONSUME ADEQUATE fluids on a daily basis (7). Yet dehydration is a major health risk for the elderly (5), and the elderly are susceptible to dehydration because of increased fluid losses (41). Aged kidneys have a decreased ability to concentrate urine (17, 27) and to conserve sodium (8), along with a relative resistance to vasopressin (25), and release less renin when challenged (6). These changes with age predispose the elderly to hypovolemia and dehydration because of the reduced ability to conserve water and sodium during times of relative water and sodium loss. The elderly have decreased thirst sensation (24, 26, 32). As a result, they are slower than young people to restore fluid balance after exercise-induced dehydration (19) and water deprivation (26). It thus appears that the elderly are more vulnerable to the consequences of physiological challenges to body fluid homeostasis and that diminished thirst in the elderly contributes to their problems of fluid balance (15).The capacities of the aging kidney have been extensively investigated in rat models of aging. As in elderly humans, kidneys of aging r...

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Section: Discussionmentioning

confidence: 95%

Thirst and salt appetite responses in young and old Brown Norway rats

Thunhorst

Johnson²

2003

American Journal of Physiology-Regulatory, Integrative and Comp

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“…This may indicate that old rats are less able to adjust to the stress of the testing situation than young and middle-aged rats. Others (36) have noted increased variability in the responses of old rats due to increased "handling stress" during testing. The variability in responding by older rats, and presumably the stress involved in testing, can be reduced by extensive preexperimental handling (36).…”

Section: Discussionmentioning

confidence: 99%

“…Others (36) have noted increased variability in the responses of old rats due to increased "handling stress" during testing. The variability in responding by older rats, and presumably the stress involved in testing, can be reduced by extensive preexperimental handling (36). Similarly, we have observed highly variable daily water intakes in old rats compared with young rats upon initial receipt from the supplier, which we attributed to shipping stress or a response to the novel laboratory environment (40).…”

Section: Discussionmentioning

confidence: 99%

Hypotension- and osmotically induced thirst in old Brown Norway rats

Thunhorst¹,

Beltz²,

Johnson³

2009

American Journal of Physiology-Regulatory, Integrative and Comp

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Thunhorst RL, Beltz TG, Johnson AK. Hypotension-and osmotically induced thirst in old Brown Norway rats. Am J Physiol Regul Integr Comp Physiol 297: R149 -R157, 2009. First published May 6, 2009 doi:10.1152/ajpregu.00118.2009.-Compared to young cohorts, old rats drink less water in response to several thirst-inducing stimuli. In these experiments, we characterized water drinking in response to hypotension and cellular dehydration in young (4 mo), middle-aged adult (12 mo) and old (29 -30 mo) male Brown Norway rats. We injected the vasodilator, minoxidil as an intravenous bolus in a range of doses (0 -20 mg/kg), so that drinking responses could be compared at equivalent reductions of arterial pressure. Old rats had greatly diminished reflex tachycardia and became significantly more hypotensive after minoxidil compared with young and middle-aged rats. When compared at equivalent reductions of arterial pressure, old rats drank one-third as much as middle-aged rats, and one-fifth as much as young rats. In addition, there were age-related deficits in drinking in response to a range of administered loads of sodium (0.15-2 M NaCl, 2 ml/100 g body wt). Urinary excretion of water and sodium in response to the loads was equivalent across ages. Both middle-aged and old rats were less able than young rats to repair their water deficits after sodium loading, attributable almost entirely to their reduced drinking responses compared with young rats. Lastly, agerelated declines in drinking appeared to be more severe in response to hypotension than in response to cellular dehydration. aging; drinking; diuresis; natriuresis; dehydration; blood pressure; heart rate ELDERLY PEOPLE AND OLD ANIMALS have impaired drinking responses to many thirst-inducing challenges (21, 23, 25, 28, 29, 33-35, 40, 41). However, the nature of the underlying causes of reduced drinking that accompanies old age, such as impaired neural or humoral signaling mechanisms, remain largely undetermined. Knowledge of the causes of age-related declines in drinking will increase our understanding of the ways to help the elderly maintain better fluid homeostasis. This is an important consideration for an increasingly aging population and for the relationship between hydrational status and disorders, such as heat-related injury.Hypotension is a potent stimulus of thirst in rats (e.g., 10,17,18,26,30,38). Thirst following hypotension is due mainly to release of renin and formation of ANG II in the circulation (26, 38; for a review, see Ref. 20) and is blocked by interfering with the actions of, or formation of, ANG II (10,26,33,38). There are conflicting reports about whether old rats drink less in response to hypotension. For example, old rats have been found to drink less after subcutaneous injections of isoproterenol compared with young rats (24, 34, 37), although not always (25,34). These previous studies did not record arterial pressure or control for differences in arterial pressure that may occur with aging (24,25,34,37). This information is important becau...

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“…Recently, an in vitro study showed that oxytocin is able to trigger ACTH release from corticotropes via action at V1 receptors (Schlosser et al 1994). However, so far, the role of oxytocin in HPA system regulation is controversial (Fliers et al 1985, Silverman et al 1990, Neumann et al 1999.…”

Section: Discussionmentioning

confidence: 99%

Endogenous vasopressin contributes to hypothalamic-pituitary-adrenocortical alterations in aged rats

Hatzinger¹,

Wotjak²,

Naruo³

et al. 2000

Journal of Endocrinology

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The ageing process in animals and humans is thought to be accompanied by a gradual impairment of corticosteroid receptor function, which is reflected by increased pituitary-adrenocortical hormone secretion at baseline and a number of aberrant neuroendocrine function test results. The latter include the ACTH and corticosteroid responses to a combined dexamethasone (DEX)/corticotropinreleasing hormone (CRH) challenge. The excessive hormonal response to this test among aged individuals has been taken as indirect evidence of enhanced endogenous arginine vasopressin (AVP) release, which -together with peripherally administered CRH -is capable of overriding DEX-induced ACTH suppression. The current study was designed to explore the role of endogenous AVP in mediating excessive hypothalamic-pituitaryadrenocortical (HPA) activity in ageing. The combined DEX/CRH test was administered to aged (22-24 months old) Wistar rats and the effect of the AVP type 1 (V1) receptor antagonist, d(CH 2 ) 5 Tyr(Me)AVP, on ACTH release was studied. Infusion of the V1 receptor antagonist after DEX pretreatment and before CRH administration prevented the CRH-induced rise in ACTH secretion in comparison with vehicle-treated aged rats (area under the concentration-time curve: 699 479 versus 2896 759; P<0·01). This difference was absent in young (3 months old) control rats.In situ hybridization showed an increased number of AVP mRNA-expressing neurons in the parvocellular but not the magnocellular, portion of the hypothalamic paraventricular nucleus in DEX-pretreated aged rats. The number and synthetic activity of parvocellular neurons expressing CRH mRNA was also increased. We have concluded that the increased HPA activity in aged rats involves enhanced synthesis and release of AVP from parvocellular neurons, possibly secondary to impaired corticosteroid receptor function.

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Physiological and Biochemical Indices of Neurohypophyseal Function in the Aging Fischer Rat

Cited by 26 publications

References 33 publications

Thirst and salt appetite responses in young and old Brown Norway rats

Thirst and salt appetite responses in young and old Brown Norway rats

Hypotension- and osmotically induced thirst in old Brown Norway rats

Endogenous vasopressin contributes to hypothalamic-pituitary-adrenocortical alterations in aged rats

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