Senescent Rats Research Articles

Resistance to silica-induced lung fibrosis in senescent rats: role of alveolar macrophages and tumor necrosis factor-α (TNF)

The purpose of the present study was to investigate the effect of aging on silica-induced lung toxicity. In young animals silica induced a significant increase in bronchoalveolar lavage tumor necrosis factor-alpha (TNF), lactate dehydrogenase as well as in cell numbers, which correlate with increased collagen deposition and silicotic nodules formations. In old rats, however, no changes in bronchoalveolar lavage or lung parameters were observed following silica instillation. These in vivo results were also confirmed in vitro, where silica failed to induce TNF release in alveolar macrophages obtained from old animals. This defective response to silica could be explained with defective protein kinase C translocation, due to a reduction in its anchoring protein RACK-1 with aging. Overall, these data indicate that the understanding of the molecular mechanisms undelaying toxicity is crucial to define the influence of age on the toxic response and progression of the disease.

Enhanced potential for oxidative stress in livers of senescent rats by the peroxisome proliferator-activated receptor alpha agonist perfluorooctanoic acid

Aging sensitizes the liver to the hepatocarcinogenic effect of PPARα agonists via unknown mechanisms. This study was designed to investigate age-dependent, hepatic effects of the non-metabolizable PPARα agonist perfluorooctanoic acid (PFOA) on the delicate balance between activities of pathways involved in H 2O 2 production and elimination. Male Fischer-344 rats, ranging in age from juvenile (4 weeks old), post puberty (10 weeks old), mature adulthood (20 weeks old), middle age (50 weeks old), to senescence (100 weeks old), were treated intragastrically with either 150 mg PFOA/kg in 0.5 ml corn oil, or with corn oil alone. Animals were sacrificed at predetermined time-points ranging from 0–28 days post PFOA or oil administration. Hepatic peroxisomal β-oxidizing activities were significantly elevated (four- to six-fold) in all age groups by PFOA. While levels declined to near basal values within 3–7 days in 4 and 10, they remained elevated for an additional week in 20-, 50- and 100-week-old rats. However, catalase activity was significantly lower in senescent livers compared with all other groups. In conclusion, aging does not appear to hinder the capacity of the liver to produce excess H 2O 2 through peroxisomal β-oxidation upon exposure to PPAR agonists. However, the reduced ability of the senescent liver to recover from PFOA-induced potential increase in H 2O 2 production, coupled with the apparent diminished capacity of this liver to decompose H 2O 2, enhances the potential for hepatic oxidative damage in aged animals. This may explain the enhanced susceptibility of the senescent liver to the hepatocarcinogenic effect of PPAR agonists.

Preservation of motor neuron Ca2+ channel sensitivity to insulin-like growth factor-1 in brain motor cortex from senescent rat.

Despite the multiple effects on mammals during development, the effectiveness of the insulin-like growth factor-1 (IGF-1) to sustain cell function and structure in the brain of senescent mammals is almost completely unknown. To address this issue, we investigated whether the effects of IGF-1 on specific targets are preserved at later stages of life. Voltage-gated Ca2+ channels (VGCC) are well-characterized targets of IGF-1. VGCC regulate membrane excitability and gene transcription along with other functions that have been found to be impaired in the brain of senescent rodents. As the voluntary control of movement has been reported to be altered in the elderly, we investigated the expression, function and responsiveness of high (HVA)- and low-voltage-activated (LVA) Ca2+ channels to IGF-1, using the whole-cell configuration of the patch-clamp and RT-PCR in the specific region of the rat motor cortex that controls hindlimb muscle movement. We detected the expression of alpha 1A, alpha 1B and alpha 1E genes encoding the HVA Ca2+ channels P/Q, N and R, respectively, but not alpha 1C, alpha 1D, alpha 1S encoding the L-type Ca2+ channel in this region of the brain cortex. IGF-1 enhanced Ca2+ channel currents through P/Q- and N-type channels but not significantly through the R-type or LVA channels. IGF-1 enhanced the amplitude but did not modify the voltage dependence of Ca2+ channel currents in young (2- to 4-week-old), young adult (7-month-old) and senescent (28- to 29-month-old) rats. These results support the concept that despite the reported decrease in circulating (liver) and local (central nervous system) production of IGF-1 with ageing, key neuronal targets such as the VGCC remain responsive to the growth factor throughout life.

Journal-related Activities at the 2003 American Society of Anesthesiologists Annual Meeting

Journal-related Activities at the 2003 American Society of Anesthesiologists Annual Meeting

Urea transporter expression in aging kidney and brain during dehydration.

Aging is commonly associated with defective urine-concentrating ability. The present study examined how the kidney and the brain of senescent (30-mo-old) female WAG/Rij rats respond to dehydration induced by 2 days of water deprivation in terms of urea transporter (UT) regulation. In euhydrated situation, senescent rats exhibited similar vasopressin plasma level but lower urine osmolality and papillary urea concentration and markedly reduced kidney UT-A1, UT-A3, and UT-B1 abundances compared with adult (10-mo-old) rats. Senescent rats responded to dehydration similarly to adult rats by a sixfold increase in vasopressin plasma level. Their papillary urea concentration was doubled, without, however, attaining that of dehydrated adult rats. Such an enhanced papillary urea sequestration occurred with a great fall of both UT-A1 and UT-A3 abundances in the tip of inner medulla and an increased UT-A1 abundance in the base of inner medulla. UT-A2 and UT-B1 were unchanged. These data suggest that the inability of control and thirsted senescent rats to concentrate urine as much as their younger counterparts derives from lower papillary urea concentration. In aging brain, UT-B1 abundance was increased twofold together with a fourfold increase in aquaporin-4 abundance. Dehydration did not alter the abundance of these transporters.

Up-regulation of cardiac nitric oxide synthase 1-derived nitric oxide after myocardial infarction in senescent rats.

Nitric oxide (NO) has been implicated in the development of heart failure, although the source, significance, and functional role of the different NO synthase (NOS) isoforms in this pathology are controversial. The presence of a neuronal-type NOS isoform (NOS1) in the cardiac sarcoplasmic reticulum has been recently discovered, leading to the hypothesis that NOS1-derived NO may notably alter myocardial inotropy. However, the regulation and role(s) of NOS1 in cardiac diseases remain to be determined. Using an experimental model of myocardial infarction (MI) in senescent rats, we demonstrated a significant increase in cardiac NOS1 expression and activity in MI, coupled with the translocation of this enzyme to the sarcolemma through interactions with caveolin-3. The enhanced NOS1 activity counteracts the decrease in cardiac NOS3 expression and activity observed in heart failure. We demonstrated an increased interaction between NOS1 and its regulatory protein HSP90 in post-MI hearts, a potential mechanism for the higher NOS1 activity in this setting. Finally, preferential in vivo inhibition of NOS1 activity enhanced basal post-MI left ventricular dysfunction in senescent rats. These results provide the first evidence that increased NOS1-derived NO production may play a significant role in the autocrine regulation of myocardial contractility after MI in aging rats.

Forebrain and brain stem neural circuits contribute to altered sympathetic responses to heating in senescent rats.

Acute heating in young rats increases visceral sympathetic nerve discharge (SND); however, renal and splanchnic SND responses to hyperthermia are attenuated in senescent compared with young Fischer 344 (F344) rats (Kenney MJ and Fels RJ. Am J Physiol Regul Integr Comp Physiol 283: R513-R520, 2002). Central mechanisms by which aging alters visceral SND responses to heating are unknown. We tested the hypothesis that forebrain neural circuits are involved in suppressing sympathoexcitatory responses to heating in chloralose-anesthetized, senescent F344 rats. Renal and splanchnic SND responses to increased (38 degrees C-41 degrees C) internal temperature were determined in midbrain-transected (MT) and sham-MT young (3-mo-old), mature (12-mo-old), and senescent (24-mo-old) F344 rats and in cervical-transected (CT) and sham-CT senescent rats. Renal SND remained unchanged during heating in MT and sham-MT senescent rats but was increased in CT senescent rats. Splanchnic SND responses to heating were higher in MT vs. sham-MT senescent rats and in CT vs. MT senescent rats. SND responses to heating were similar in MT and sham-MT young and mature rats. Mean arterial pressure (MAP) was increased during heating in MT but not in sham-MT senescent rats, whereas heating-induced increases in MAP were higher in sham-MT vs. MT young rats. These data suggest that in senescent rats suppression of splanchnic SND to heating involves forebrain and brain stem neural circuits, whereas renal suppression is mediated solely by brain stem neural circuits. These results support the concept that aging alters the functional organization of pathways regulating SND and arterial blood pressure responses to acute heating.

Age-related vulnerability to diencephalic amnesia produced by thiamine deficiency: the role of time of insult

Age is a risk factor for the development of many neurological disorders, including alcohol-related neurological disorders. A rodent model of Wernicke-Korsakoff Syndrome (WKS), acute pyrithiamine-induced thiamine deficiency (PTD), produces diencephalic damage and impairments of memory similar to what is seen in WKS patients. Advanced age increases the vulnerability to the cascade of acute and some chronic neurological events caused by PTD treatment. Interactions between PTD treatment and age at the time of treatment (3, 10, or 21 months), in addition to the effects of an increased recovery period, were examined relative to spatial memory impairment and neuropathology in Fischer 344 rats. Although acute neurological disturbances and medial thalamic brain lesions were more prevalent in middle-aged and senescent rats exposed to PTD treatment, relative to young rats, behavioral data did not support the view that PTD and aging have synergistic effects. In addition, both advanced age and PTD treatment result in a loss of basal forebrain cholinergic neurons, though there was no interaction. Despite the fact that no convincing evidence was found for an effect of extended recovery time on neuropathology measures, young rats given an extensive recovery period displayed less working memory impairment. In summary, these data provide evidence for an increased susceptibility of the aged rat to the acute neurological consequences and diencephalic pathology associated with PTD treatment and indicated a similar vulnerability of the middle-aged rat. However, the synergistic interaction between aging and PTD treatment in thalamic tissue loss did not express behaviorally.

Age-related decreases in the response of aquaporin-5 to acetylcholine in rat parotid glands.

Aquaporin-5 (AQP5) is important in salivary fluid secretion in response to cholinergic and adrenergic stimuli in rat parotid glands. We hypothesized that expression and function of AQP5 might change with age. Acetylcholine and epinephrine induced increases in AQP5 levels in the apical plasma membranes of both young adult and senescent rats. The stimulatory effect of acetylcholine, but not that of epinephrine, on AQP5 levels in the apical plasma membranes of the cells decreased markedly during aging. The quinuclidine derivative, SNI-2011, induced a persistent increase in AQP5 levels in the apical plasma membrane in the cells of both these rats. The amounts of M(3)-muscarinic receptor and Gq proteins did not decrease during aging. The age-related alteration in the responsiveness of AQP5 in the cells to these stimuli might account for the concomitant changes in nitric oxide synthase activity. These results suggest that SNI-2011 might have therapeutic benefit for the treatment of age-related xerostomia.

Dietary selenium intake affects cardiac susceptibility to ischaemia/reperfusion in male senescent rats.

cardiovascular ageing is associated with an increase in cardiac susceptibility to ischaemia and reperfusion. This has been suggested to be partly related to an increased sensitivity of the myocardium to the reactive oxygen species that are produced during post-ischaemic reperfusion. The aim of the present study was therefore to determine whether increasing cardiac glutathione peroxidase activity by a selenium-enriched diet could afford some protection against ischaemia and reperfusion to senescent rat hearts. 22 months old male Wistar rats received either a high-selenium (1.5 mg Se/kg diet) or a low-selenium (0.05 mg Se/kg diet) diet for 10 weeks. At the end of the diet, hearts were submitted to ischaemia and reperfusion ex vivo and either fixed for semi-quantitative analysis of ultrastructural damage by electron microscopy or used for glutathione peroxidase activity assessment. high-selenium supply increased cardiac total, mitochondrial and cytosolic glutathione peroxidase activities. Moreover, this diet induced a significant improvement of cardiac post-ischaemic functional recovery. Finally, this preservation of cardiac function was associated with a significant limitation of ultrastructural alterations of sarcomeres and mitochondria. our high-selenium diet considerably limits the sensitivity of senescent rat hearts to ischaemia and reperfusion. This finding suggests that peroxides might play a key role in the increase in cardiac sensitivity to ischaemia and reperfusion during ageing. Together with the observation that selenium status decreases with age in humans, our results indicate that reinforcing selenium supply could improve the prognosis of cardiovascular diseases in old patients.

Age-Associated Changes in Histology and Gene-Expression Profile in the Rat Ventral Prostate

The incidence of prostate diseases rises dramatically with age in men, yet little is understood of the mechanisms underlying prostatic senescence and its contribution to disease development in the gland. In Noble rats, aging of the ventral prostate (VP) is characterized morphologically by widespread atrophy of acini, increased accumulation of concretions in glandular lumen, infiltration of inflammatory cells, and focal epithelial atypia. We used a cDNA microarray containing 2388 known transcripts, together with the Tyramide Amplification System and t statistics, to identify differentially expressed genes in the VPs of young (3 months old) and old (16 months old) rats. A total of 78 VP genes were found to be differentially expressed by the two groups; in old rats, 65 VP genes (83%) showed reduced expression and 13 genes (17%) showed increased expression compared with young animals. The age-dependent underexpressed genes fell into several functional clusters: those involved in amino-acid metabolism, protein synthesis, protein secretion and degradation, vesicle/membrane trafficking, energy metabolism, signal transduction, spermidine and spermine syntheses, and cellular defense against stress. The overexpressed genes included iduronate 2-sulfatase, HLA class I locus C heavy chain, membrane cofactor protein of the complement system, TRPM-2, cadherin-associated protein-related, and X-CGD. Post hoc analyses confirmed a progressive decline in the expression of ribophorin II and BiP and a gradual increase in the expression of TRPM-2 in rat VPs as animals aged from 3 to 19 months old. In conclusion, the observed widespread declines in expression of genes involved in protein synthesis, protein fidelity maintenance, anabolism, growth inhibition, and energy metabolism, together with increased expression of genes implicated in cell survival in the VPs of senescent rats, may help explain the susceptibility of the prostates of elderly men to development of disease.

Norepinephrine release in brown adipose tissue remains robust in cold-exposed senescent Fischer 344 rats.

Near the end of life, old F344 rats undergo a transition, marked by spontaneous and rapidly declining function. Food intake and body weight decrease, and these rats, which we call senescent, develop severe hypothermia in the cold due in part to blunted brown fat [brown adipose tissue (BAT)] thermogenesis. We tested the hypothesis that this attenuation may involve diminished sympathetic signaling by measuring cold-induced BAT norepinephrine release in freely moving rats using linear microdialysis probes surgically implanted into interscapular BAT 24 and 48 h previously. In response to 2 h at 15 degrees C, senescent rats increased BAT norepinephrine release 6- to 10-fold but did not maintain homeothermy. This increase was comparable to that of old presenescent (weight stable) rats that did maintain homeothermy during even greater cold exposure (2 h at 15 degrees C followed by 1.5 h at 8 degrees C). Tail temperatures, an index of vasoconstrictor responsiveness to cold, exhibited similar cooling curves in presenescent and senescent rats. Thus cold-induced sympathetic signaling to BAT and tail vasoconstrictor responsiveness remain robust in senescent rats and cannot explain their cold-induced hypothermia.

Recovery of slow skeletal muscle after injury in the senescent rat

We studied the contractile, histological and biochemical characteristics of regenerating slow (soleus) muscles of aged rats and the effect of IGF-1 treatment on these parameters. Regenerating soleus muscles were studied 21 days after myotoxic injury. In senescent rats (24 month old), the in situ isometric maximal tetanic force (P0), resistance to fatigue (T20%P0) and shortening speed with an afterload of 20%P0 (SS20%P0) were lower ( p<0.05) in regenerating soleus muscles as compared to uninjured controlateral soleus muscles. Moreover, the expression of type 1 myosin heavy chain (MHC-1) was decreased by injury in the soleus muscles of senescent rats ( p<0.05). Furthermore, a single injection of IGF-1 (3 μg) into the soleus of senescent rats only slightly increased the level of sarcoplasmic reticulum type 2 Ca 2+-ATPase in regenerating soleus muscles ( p<0.01). Contrary to senescent animals, regenerating soleus of adult rats (10 month old) did not present significantly lower P0 and MHC-1 expression than uninjured controlateral muscles ( p>0.05). In conclusion, the regeneration of a slow muscle is more uncompleted 3 weeks after myotoxic injury in senescent rats than in adult rats. It cannot be made more effective by a single injection of IGF-1 into the senescent slow muscle.

Effect of increased dietary selenium intake on blood and cardiac selenium status during aging in rats

Oral selenium supplementation has been described as cardioprotective against pathophysiological situations involving oxidative stress in young adults rats. However no data are available concerning the effects of selenium supplementation on selenium status and glutathione peroxidase (GPX) activity in senescent rats. In the present study young adult and senescent rats were fed a diet containing selenium either 0.05 mg/kg (control) or 1.5 mg/kg (selenium) for 10 weeks. Selenium content in both diets was adjusted by sodium selenite addition. At the end of the supplementation period although plasma selenium level was lower in the two groups of aged rats than in the corresponding adults (p < 0.05), cardiac GPX activity, measured in both cytosolic and mitochondrial extracts appeared to be similarly increased in both categories of age. These data are the first to indicate that oral Se-supplementation is able to increase the plasma selenium concentration and cardiac GPX activity in senescent rats as well as in young adults.

Dynamic MRI reveals that the magnitude of the ischemia-related enhancement in skeletal muscle is age-dependent.

This study was designed to evaluate the influence of age on the dynamic contrast-enhanced MRI of ischemic tissue. A well-established model of peripheral arterial insufficiency (i.e., the rat hindlimb ischemia after removal of femoral artery) in different age groups (i.e., young, presenescent, and senescent rats) was studied. The analysis of the MR signal demonstrated a marked accumulation of a contrast agent (Gd-DTPA) in the ischemic leg (ischemia-related enhancement, IRE). IRE was an age-related event: 4-month-old rats showed a strong IRE while 12-month-old rats and 20-month old rats showed a significantly reduced IRE in comparison to young animals. Histological analysis of the ischemic muscles revealed that there was no evidence of significant necrosis of the muscle tissue but only a weak interstitial fibrosis; CD31-immunostaining revealed a preserved microcirculatory bed.

Effect of Starvation on Organ Blood Flow in the Senescent Rat

Effect of Starvation on Organ Blood Flow in the Senescent Rat

Basis for the age-related decline in intestinal mucosal immunity.

The elderly are characterized by mucosal immunosenescence and high rates of morbidity and mortality associated with infectious diseases of the intestinal tract. Little is known about how the differentiation of immunoglobulin A (IgA) plasma cells in Peyer's patches (PPs) and their subsequent homing to the small intestinal lamina propria (LP) is affected by aging. Quantitative immunohistochemical analyses demonstrated a 2-fold increase in the number of IgA+ cells in the PPs, coupled with significant declines in the numbers of IgA+ and antibody-positive cells in the intestinal LP of senescent rats compared to young adult animals. These data suggest that aging diminishes the emigration of IgA immunoblasts from these lymphoid aggregates, as well as their migration to the intestinal LP. Flow cytometry and lymphocyte adoptive transfer studies showed 3- to 4-fold age-related declines in the homing of antibody-containing cells and mesenteric lymph node lymphocytes to the small intestines of rhesus macaques and rats, respectively. The number of peripheral blood IgA immunoblasts expressing the homing molecule α4β7 declined 30% in senescent rats. This was accompanied by a >17% decrease in the areal density of LP blood vessels staining positive for the cell adhesion molecule MAdCAM-1. Cumulatively, declines in expression of these homing molecules constitute a substantial age-related diminution of IgA immunoblast homing potential. In vitro antibody secretion by LP plasma cells, i.e. antibody secreted per antibody-positive cell, remains unchanged as a function of donor age. Intestinal mucosal immunosenescence is a consequence of reduced homing of IgA plasma cells to the intestinal LP as a result of declines in homing molecule expression.

The optic nerve head region of the aged rat: An immunohistochemical investigation

Purpose. To study age-related changes in the rat optic nerve head. Methods. Eyes of young (2 months) and senescent (20 months) Wistar rats were stained with antibodies against collagen type I, III, IV, VI, laminin, glial fibrillary acidic protein (GFAP) and connexin 43. Results. In the senescent animals, an increase of collagen type I and VI, and of connexin 43 was observed in the lamina cribrosa region. In addition, connexin 43 was newly formed in the optic nerve sheath of old animals. Collagen type III and IV, laminin and GFAP did not show age-related alterations. Conclusion. The described changes differ substantially from those described in the rat glaucoma model. As the rodent age-related changes are similar to those found in the human lamina cribrosa, the rat model seems to be useful for studying the influence of age on the onset of glaucoma.

Differential response of cardiac fibroblasts from young adult and senescent rats to ANG II.

The intracardiac ANG II-forming pathway is activated in the senescent myocardium, raising the possibility of enhanced ANG II effects on cardiac fibroblasts. This study established an in vitro model of cultured cardiac fibroblasts from aged rats to examine if the response of these cells to ANG II is modified in the aged heart. Levels of mRNA encoding renin, angiotensinogen, and the AT(1) receptor subtype in cardiac fibroblasts from young adult and senescent rats were quantified by RT-PCR, net collagen production by a hydroxyproline-based assay, and transforming growth factor (TGF)-beta levels using a commercial kit. In cardiac fibroblasts from young adult rats, ANG II significantly enhanced AT(1) mRNA levels, net collagen production, and TGF-beta production. In fibroblasts from the aged myocardium, ANG II downregulated AT(1) mRNA expression, had a less pronounced effect on net collagen production, and had no effect on TGF-beta production. Such age-related modification of the response of cardiac fibroblasts to ANG II may counteract the effects of augmented intracardiac ANG II production in the senescent heart, limiting fibrogenesis.

Ageing exacerbates the cardiotoxicity of hydrogen peroxide through the Fenton reaction in rats

Reactive oxygen species (ROS) are involved in the post-ischemic reperfusion syndrome of the myocardium. Moreover, ageing is associated with an increased cardiac sensitivity to both ischemia and reperfusion. The aim of the present study was to determine whether the lower tolerance of aged hearts to reperfusion could be due to an increased sensitivity to the ROS that are produced during the early phase of reperfusion. For this purpose isolated perfused hearts from adult (4 months) and aged (24 months) rats were perfused with a buffer containing 150 μM of hydrogen peroxide (H 2O 2) in presence or absence of deferoxamine mesylate (150 μM), an iron chelator. H 2O 2 perfusion was continued until left ventricular developed pressure had decreased up to 20% of its initial value. Ageing led to a significant reduction of the duration of the H 2O 2 perfusion required for inducing a 80% functional alteration. Although deferoxamine did not affect this parameter in adult rats, it significantly increased the duration of H 2O 2-perfusion in senescent hearts (control: 14.0±0.9 min vs. deferoxamine: 18.1±1.0, P<0.05). Similarly, ageing aggravated cardiac contracture induced by H 2O 2-perfusion. Again, deferoxamine, which had no effect on this parameter in young adult hearts, significantly reduced the contracture of senescent rat hearts. To conclude, our data clearly show that ageing is associated with an increased sensitivity of the myocardium to hydrogen peroxide, which is partly reversed by iron chelation. These results suggest that the iron-catalyzed Fenton reaction producing hydroxyl radicals might be greater in hearts from senescent rats than in hearts from young adults.