Effect of age on the expression of antioxidant enzymes in male Fischer F344 rats

Age-related changes in the activities of superoxide dismutase, catalase, and glutathione peroxidase were determined in brain, heart, hepatocytes, intestinal mucosa, and kidney from male Fischer F344 rats. Superoxide dismutase activity decreased significantly with age in all five tissues studied. The activity of catalase decreased with age in brain, hepatocytes, and kidney while glutathione peroxidase activity decreased significantly with age only in intestinal mucosa and kidney. The relative levels of superoxide dismutase, catalase, and glutathione peroxidase mRNA were measured in brain, hepatocytes, and kidney. An age-related decrease in SOD and catalase mRNA was observed for brain, hepatocytes, and kidney. GPX mRNA levels decreased with age in hepatocytes and kidney but did not change with age in brain. In general, the age-related changes in the activities of SOD, catalase, and GPX were paralleled by a similar change in the relative level of the mRNAs coding for these enzymes.     

Dose-dependent renal tubular toxicity of harman and norharman in male F344 rats.

The renal toxicity of harman and norharman, administered for 2 or 4 weeks at dietary levels of 1,000, 500, or 0 parts per million (ppm), was investigated in 6-week-old male F344/DuCrj rats. Although rats fed 1,000 ppm harman or norharman, but not the 500 ppm level, demonstrated marked body weight retardation from 1 week to termination, no mortalities occurred. Marked elevation of water consumption was evident in rats given harman or norharman at 1,000 ppm, but not at 500 ppm, together with large increases in urine of low specific gravity. Urinary lysosomal enzymes (N-acetyl-beta-D-glucosaminidase, NAG, and lactate dehydrogenase, LDH) and sugar levels were increased, and the brush border enzymes (gamma-glutamyl transpeptidase, GGT, and alkaline phosphatase, ALP) decreased. Furthermore, serum biochemistry revealed clear elevation of parameters indicating renal toxicity in these rats. Histopathologically, rats fed 1,000 ppm harman or norharman, but not 500 ppm, demonstrated focal toxic renal degenerative/necrotic and regenerative lesions in proximal, distal, and collecting tubules. These changes were associated with a clearly increased labeling index (LI) of the nuclei of renal tubular epithelial cells on immunohistochemical staining for 5-bromo-2'-deoxyuridine (BrdU). Chemical specific crystal formation within tubular lumina was evident in rats fed 1,000 ppm, but not 500 ppm, this being considered the cause of the renal tubular lesions. It was concluded that harman and norharman exert renal toxicity at the dietary level of 1,000 ppm, but not 500 ppm, in male F344 rats.     

Effect of long-term caloric restriction on brain monoamines in aging male and female Fischer 344 rats

The present study examines the changes in central monoamines and their metabolites in aged male and female rats after long-term caloric restriction. Fischer 344 rats of both sexes (n = 5-10/group) were maintained on one of two dietary regimens: ad libitum NIH 31 diet or 60% by weight of the ad lib. intake (restricted), supplemented with vitamins and minerals. Animals received these diets from the age of 14 weeks until killed at 22.25 months of age. Caudate nucleus (CN), hypothalamus (HYPO), olfactory bulb (OB) and nucleus accumbens (NA) were assayed for content of norepinephrine (NE), dopamine (DA) and its metabolites (dihydroxyphenylacetic acid, DOPAC, and homovanillic acid, HVA) and serotonin (5-HT) and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) using HPLC/EC. Relative to the ad lib. group, restricted rats of both sex showed significant decreases in NE content in CN, HYPO and OB. DA and 5-HT content were decreased significantly in the CN and HYPO. No significant changes were found in the levels of DA metabolites in all brain regions studied. While the 5-HIAA level was significantly reduced in the HYPO and NA of the female restricted rats, it was increased several-fold in the OB of the male restricted animals. These preliminary results suggest that long-term caloric restriction alters brain monoamine concentrations, an effect which may in turn modify the normal rate of aging.     

Age-related cell proliferation and apoptosis in the kidney of male Fischer 344 rats with observations on a spontaneous tubular cell adenoma

Cell proliferation rate and apoptosis were examined in archival kidneys from young, middle-aged, and old male F344 rats. Immunohistochemical expression of proliferating cell nuclear antigen (PCNA) and apoptosis were quantified in the same cell populations of the proximal tubule epithelium. A total of 79 kidneys from 40 rats were examined. There was a progressive increase in cell proliferation rates in rats from 4 and 6-10 months of age. In 23-month-old rats, proliferative activity appeared to be reduced. No age-related variations in apoptotic indices were found. One of the 16 rats aged 23 months had a tubular cell adenoma. In the tumor-affected kidney, cell proliferation rate was dramatically higher than in the contralateral kidney as well as in all the other kidneys examined. This high proliferative activity was not balanced by variation in cell death.     

Effects of dietary taurine supplementation or deprivation in aged male Fischer 344 rats

Taurine is a sulfur amino acid that is present in high concentration in mammalian tissues and previously has been reported to decline in a number of tissues with advancing age. The aims of the present study were to examine: (1) the effects of dietary taurine supplementation; (2) the effects of taurine-free diets; (3) the ability of aged rats to conserve urinary taurine; and (4) the consequences of these dietary manipulations on some biochemical parameters. Male F344 rats (n = 30/group) 18 months of age were placed on control diets, diets supplemented with 1.5% taurine in the drinking water, or a taurine-free diet for 10 months. An adult control group (12 months old at the end of the study) on normal diets was included for comparison purposes. Significant (P < 0.05) age-related declines in taurine content were observed in the spleen, kidney, eye, cerebellum and serum. Taurine supplementation corrected these deficits in tissue content in aged rats and in many cases increased taurine content above that of adult controls. Urinary excretion of taurine was significantly (P < 0.05) reduced in aged rats indicating an increased need to conserve taurine. Taurine-deficient diets did not further exacerbate the age-related decline in tissue taurine content, suggesting biosynthetic adaptations to the lack of dietary taurine. Dietary taurine supplementation blunted age-related declines in serum IGF-1 and increases in serum creatinine and blood urinary nitrogen (BUN). These studies suggest that advanced aging results in a taurine-deficient state that can be corrected by dietary supplementation.     

Age-associated changes in hearts of male Fischer 344/Brown Norway F1 rats

Aging is associated with left ventricular hypertrophy, dilatation, and fibrosis of the heart. The Fischer 344/Brown Norway F1 (F344/BNF1) rat is recommended for age-related studies by the National Institutes on Aging because this hybrid rat lives longer and has a lower rate of pathological conditions than inbred rats. However, little is known about age-associated changes in cardiac and aortic function and structure in this model. This study evaluated age-related cardiac changes in male F344/BNF1 rats using ECHO, gross, and microscopic examinations. Rats aged 6-, 30-, and 36-mo were anesthetized and two-dimensional ECHO measurements, two-dimensional guided M-mode, Doppler M-mode, and other recordings from parasternal long- and short-axis views were obtained using a Phillips 5500 ECHO system with a 12 megahertz transducer. Hearts and aortas from sacrificed rats were evaluated grossly and microscopically. The ECHO studies revealed persistent cardiac arrhythmias (chiefly PVCs) in 72% (13/18) of 36-mo rats, 10% (1/10) of 30-mo rats, and none in 6-mo rats (0/16). Gross and microscopic studies showed left ventricular (LV) dilatation, borderline to mild hypertrophy, and areas of fibrosis that were common in 36-mo rats, less evident in 30-mo rats, and absent in 6-mo rats. Aging was associated with mild to moderate decreases of LV diastolic and systolic function. Thus, male F344/BN F1 rats demonstrated progressive age-related (a) decline in cardiac function (diastolic and systolic indices), (b) LV structural changes (chamber dimensions, volumes, and wall thicknesses), and (c) persistent arrhythmias. These changes are consistent with those in humans. The noninvasive ECHO technique offers a means to monitor serial age-related cardiac failure and therapeutic responses in the same rats over designated time intervals.     

Effects of age on myosin and creatine kinase isoforms in left ventricles of Fischer 344 rats

Left ventricles of hearts from male Fischer 344 rats of 2, 8 and 23 months of age were analyzed to determine if aging results in significant alterations in the isoform distribution of myosin and creatine kinase protein and mRNAs. Left ventricles of maturing (2-month) rats contained almost exclusively alpha-myosin heavy chain (MHC) mRNA and protein. In adults (8 months) there was a 5-fold increase in beta-MHC (fetal isoform) and an approximate 10% decrease in alpha-MHC mRNA levels, relative to 2 months. By 23 months (senescence), beta-MHC mRNA levels had increased by 11-fold and alpha-MHC mRNA levels had decreased by about 30%. These changes corresponded to an increase in the relative proportion of beta-MHC protein, from undetectable levels at 2 months, to about 40% by 8 months and to about 60% by 23 months. Increased levels of beta-MHC and its mRNA in older rats correlated with decreased serum thyroid hormone levels. The specific activity of creatine kinase in crude homogenates decreased with age, as has been reported previously. Relative to 2-month controls, the specific activity of creatine kinase had decreased by 21% at 8 months and by 37% at 23 months. Analysis of creatine kinase activity showed no large increase in levels of the fetal (B) isoform with age, as was found for myosin. Levels of mRNAs encoding the B and M isoforms of creatine kinase were significantly reduced in senescent rats. Thus, the decreased levels of creatine kinase in aging rats is correlated with decreased levels of mRNA encoding the BCK and MCK isoforms but not an isoform shift.     

Spatial reference and working memory across the lifespan of male Fischer 344 rats

Loss of mnemonic function is among the earliest and most disconcerting consequences of the aging process. This study was designed to provide a comprehensive profile of spatial mnemonic abilities in male Fischer 344 (F344) rats across the lifespan. Young, middle-aged, and aged F344 rats were trained in spatial reference and working memory versions of the water maze task. There was a progressive age-related decline in spatial reference memory across the lifespan. Reliable individual differences were observed among aged rats, with some aged rats performing as well as young cohorts and others performing outside this range. An age-related delay-dependent decline was observed on a working memory version of the water maze task although no relationship between performance on reference and working memory tasks was present. Notably, middle-aged rats were impaired relative to young on both tasks. Together these data demonstrate that individual differences in spatial reference memory exist among aged F344 rats and provide novel data demonstrating an unrelated decline in working memory across the lifespan, suggesting that age-related mnemonic dysfunction may occur across multiple brain systems.     

Exogenous nerve growth factor stimulates choline acetyltransferase activity in aging Fischer 344 male rats

The effect of age and exogenous nerve growth factor (NGF) infusion on choline acetyltransferase (ChAT) specific activity is examined in microdissections of cerebral and hippocampal cortices, and the cholinergic nuclei of the medial septum and diagonal band of Broca (MS/DB), the nucleus basalis magnocellularis (NBM), and striatum of Fischer 344 male rats. Significant, 20% losses in ChAT activity are found in the MS/DB and striatum of 24-month-old rats (n = 21) compared to 4-month-old animals, but there is no apparent loss of enzyme activity in the NBM. Loss of ChAT activity in the MS/DB is only observed in animals older than 19 months of age, while a striatal deficit is found in animals older than 7 months. Treatment for 2 weeks with NGF at 1.2 micrograms/day results in significant 70% increases of ChAT activity in the MS/DB and striatum of 24-month-old rats compared to untreated and vehicle-treated 4-month-old rats, but does not stimulate activity in the NBM. Sensitivity of ChAT activity in the MS/DB and striatum to exogenous NGF increases with age. These experiments indicate that in the MS/DB, NBM, and striatum of Fischer 344 male rat there is an age-associated, differential regulation of ChAT enzyme activity and sensitivity to exogenous NGF.     

Cardiovascular responses to acute footshock stress in adult and aged Fischer 344 male rats

Tail artery catheters were surgically implanted in Fischer 344 male rats to allow for measurement of mean arterial pressure (MAP, mm Hg) and heart rate (HR, beats/min) in conscious, unrestrained rats. Basal values of MAP and HR were similar for groups of 4, 12 and 24 month old rats. Increments in Map did not differ among rats of the 3 ages following handling and transfer to a shock chamber or immediately or 5 minutes after exposure to inescapable footshock (2.0 mA, 0.6 sec duration, every 6 sec for 1 min). In contrast, there was a significant age-related attenuation of the tachycardia following handling and transfer of rats to the shock chamber and at the end of footshock. These data are consistent with previous findings of a reduced sensitivity of the aged myocardium to stress-induced sympathetic stimulation.     

Loss of N-cadherin and alpha-catenin in the proximal tubules of aging male Fischer 344 rats

Aging is associated with a loss of renal reserve, and increased sensitivity to either xenobiotic or physiologic insult. Given the critical role of the cadherin/catenin complex in establishing and maintaining the integrity and polarity of tubular epithelial cells, it was hypothesized that aging was associated with alterations in renal cadherin/catenin complexes. Histological assessment of aged (24 months) kidneys harvested from male Fischer 344 rats demonstrates mild degeneration of proximal tubules, multifocal chronic lymphocytic infiltration, moderate development of protein casts inside tubules, and tubular dilatation or degeneration. Western blot analysis revealed that N-cadherin protein expression is not constant over 24 months. N-cadherin expression increased from 4 to 9 months, with peak levels at 9 and 13 months. A decrease in expression was seen at 19 months and an almost complete loss of expression was seen at 24 months. In contrast, the expression of E- and Ksp-cadherin was constant over 24 months. A loss of alpha-catenin at was seen at 19 and 24 months in the absence of changes in beta-, gamma-, and p120-catenin. This pattern of N-cadherin expression (increase followed by decrease) was confirmed by real-time PCR analysis, which demonstrated a similar pattern as the Western blot, suggesting that the loss of N-cadherin protein was due to decreased gene expression. The loss of N-cadherin was specific for the kidney, as no changes in N-cadherin expression in the liver, brain, or testes were seen during aging. The conclusion that loss of N-cadherin expression is a critical component of the renal dysfunction associated with aging is supported by the finding that caloric restriction attenuates the loss of N-cadherin, as well as the finding that a significant loss of N-cadherin is seen in the kidneys of ZDF x SHHF rats, a genetic model of end-stage renal disease. Cadherin and catenin expression was further analyzed by immunofluorescence. A significant loss of staining of both N-cadherin and alpha-catenin was seen in the proximal tubules of rats at 24 months. Interestingly, this corresponded with delocalization of the alpha-1 subunit of the Na+K+-ATPase, i.e. aberrant staining on cell-cell borders and some indication of apical staining in proximal tubules. Taken together, these data suggest that aging is associated with decreased expression of N-cadherin and alpha-catenin and is associated with a loss of cell polarity.     

Comparison of the dominant lethal effects of acrylonitrile and acrylamide in male Fischer 344 rats

Acrylonitrile (ACN) and acrylamide (AA), structurally similarvinyl monomers, are both animal carcinogens. ACN is weakly mutagenicin bacteria and induces sister-chromatid exchange, unscheduledDNA synthesis and cell transformation in cells in culture. AAinduces chromosomal aberrations in bone marrow, blood and germcells in vivo, and dominant lethal mutations in the germ cellsof male mice and rats. In the current study, the ability ofAA and ACN to induce dominant lethal mutations in the germ cellsof male Fischer 344 rats was compared. Three groups of 50 maleswere gavaged daily for 5 days with ACN (60 mg/kg in normal saline),AA (30 mg/kg in normal saline) or vehicle only; an additionalgroup of 20 males received a single i.p. injection of 0.2 mg/kgtriethylenemelamine (TEM) on the afternoon of day 5. Starting1 day after exposure, each male was bred to one female per weekfor 4 weeks (TEM-exposed group) or 10 weeks (ACN, AA and controlgroups). Mating rates were reduced only during week 1 in theTEM-treated group; pregnancy rates were reduced only duringweek 2 in the AA-exposed group and week 4 in the TEM-treatedgroup. Females were necropsied 13 days after the end of theappropriate mating week and the amount of pre- and post-implantationloss calculated. ACN treatment of male rats induced no increasesin either pre- or post-implantation loss in females in any ofthe 10 weeks post-exposure examined. AA induced significantlyelevated amounts of post-implantation loss for 3 weeks afterexposure and pre-implantation loss for 4 weeks post-exposure;both measures returned to control values for the remaining 6weeks of the study. The positive control TEM caused both indicesto increase during all 4 weeks examined. We conclude that AAis a dominant lethal mutagen in male rat germ cells in vivo,specifically in mature spermatozoa and late-stage spermatids.In contrast, the structurally related chemical ACN has neitherfertility nor dominant lethal effects in the male Fischer 344rat after oral administration, and may not pose a significantmutagenic risk to germ cells.     

Age and organ dependent spontaneous generation of nuclear 8-hydroxydeoxyguanosine in male Fischer 344 rats

8-Hydroxydeoxyguanosine (8-OHdG) is a major oxidative DNA adduct playing roles in senescence, carcinogenesis and various disease processes. High-performance liquid chromatography with an electrochemical detection (HPLC-ECD) method has been widely used to assess organ levels of 8-OHdG, and a recently introduced immunohistochemical approach has made it possible to clarify intra-organ localization. In the present study, these methods were employed to reveal age-dependent changes in nuclear 8-OHdG within various tissues of male Fischer 344 rats between 18 fetal days and 104 weeks of age. 8-OHdG was detected in the nuclei of cerebellar small granule and small cortical cells, cerebral nerve cells, and choroid plexus epithelia of the brain and ependymal cells of the spinal cord; parenchymal cells in the anterior lobe of the pituitary and adrenal glands (mainly cortex); bronchial epithelium of the lung; intra-hepatic bile duct, pancreatic duct, glandular gastric and intestinal epithelial cells; renal tubular epithelial cells (mainly medulla); and spermatogonia and spermatocytes of the testis and seminal vesicle epithelia. The nuclear 8-OHdG levels were high (more than two lesions per 10(6) deoxyguanosines) from 7 days to 104 weeks of age in the brain, 3 to 6 weeks in the adrenal gland, 6 to 104 weeks in the lung, and 3 to 52 weeks in the testis. In the other organs, the nuclear 8-OHdG levels remained low throughout. These findings provide a basis for research dealing with oxidative stress by indicating organ-specific and age- but not aging-dependent changes in the localization of spontaneously generated nuclear 8-OHdG in intact rats. The immunohistochemical approach has advantages for assessing variation of 8-OHdG formation at the cellular level not accessible to the HPLC-ECD method.     

Effect of vanadate on renal tubular function in rats

Orthovanadate (VO4) has been shown to cause a marked natriuresis in rats. This has been ascribed to its inhibitory action on renal Na-K-ATPase activity. Because virtually all nephron segments possess Na-K-ATPase activity the administration of VO4 should alter renal tubular transport along the entire nephron. To examine this possibility, adult rats were anesthetized and infused with VO4 (10 mumol.kg body wt-1.h-1 i.v.). This dose had no effect on glomerular filtration rate, effective renal plasma flow, and blood pressure, whereas urine flow and sodium and water excretion rose markedly. Potassium excretion remained unaltered. VO4 depressed only maximal bicarbonate and glucose reabsorption without causing a glucose or bicarbonate "leak" at normal levels of blood glucose or bicarbonate. In acutely thyroparathyroidectomized rats VO4 produced a striking phosphaturia, not accompanied by an increase in nephrogenous cAMP excretion. Both free water clearance in Brattleboro rats and free water reabsorption in normal rats was significantly depressed by VO4. These data demonstrate that VO4 depresses tubular reabsorption in proximal and distal nephron segments. We conclude that VO4 exerts its effect on tubular function by inhibition of Na-K-ATPase activity.     

Hippocampal neuronal necrosis in control Fischer 344 rats

Brain tissue sections from control male and female Fischer 344 (F344) rats from ten National Toxicology Program (NTP) Bioassays were histomorphologically reviewed for non-neoplastic lesions of the hippocampus. Unilateral segmental hippocampal neuronal necrosis, which has not been reported in normal rats, was observed in 9 of 433 (2.1 per cent) males and 1 of 454 (0.2 per cent) females. Significant coexisting lesions were left-sided atrial and/or valvular thrombosis, metastatic mesothelioma, and large lymphocyte leukaemia. These data suggest that this naturally occurring lesion of predominantly aged male rats may result from an impairment of cerebral perfusion secondary to vascular obstruction by thrombotic emboli or leukaemic cells and haemolytic anaemia concomitant with large lymphocyte leukaemia, which commonly occurs in F344 rats.     

Effect of chronic caloric restriction on hepatic enzymes of intermediary metabolism in the male Fischer 344 rat

It is well established that caloric restriction extends life span and significantly retards the rate of occurrence of most age-associated degenerative disease processes. A paucity of data exists relative to the mechanisms by which caloric restriction accomplishes these events. We have examined the effect of caloric restriction in rats on several hepatic enzymes of intermediary metabolism. The activities of glycolytic and supporting enzymes including lactate dehydrogenase, pyruvate kinase, sorbitol dehydrogenase, and alcohol dehydrogenase were all decreased in response to caloric restriction. Fructose 1-phosphate aldolase and creatine phosphokinase were not altered. Likewise, enzymes associated with lipid metabolism (malic enzyme and glycerokinase) were reduced (fatty acid synthetase was reduced, but not to a statistically significant degree). Activities of enzymes supporting gluconeogenesis (glutamate oxaloacetate transaminase, tyrosine aminotransferase, glutamate pyruvate transaminase, glutamate dehydrogenase, amino acid oxidase, malate dehydrogenase, and glucose 6-phosphatase) were either unchanged or increased significantly by caloric restriction. Glucagon levels were decreased. Comparisons between young ad libitum fed and older calorically restricted rats revealed similar but not identical metabolic activity. These results suggest that caloric restriction produces an effect on intermediary metabolism, favoring the role of glucagon and glucose synthesis; but limiting the role of insulin and glucose catabolism in the liver. The former observation provides for the efficient support of peripheral tissues and the latter a level of energy production necessary only for self maintenance. Limited lipid metabolism suggests decreased potential for fatty acid epoxide formation and free radical damage to cellular macromolecules. Additionally, caloric restriction may delay the progressive age associated changes in the activities of some of the enzymes investigated.     

Neurochemical, endocrine and immunological responses to stress in young and old Fischer 344 male rats

Two experiments were performed. In the first, a 20 min conditioned emotional response (CER) paradigm was used to compare the neurochemical, endocrine and immunological responses to stress of 7- and 22-month-old Fischer 344 (F344) male rats. In the second, corticosterone levels 20 min following ether stress, and regional brain type I and II corticosterone receptor densities were examined using 7- and 17.5-month-old F344 male rats. Dopamine (DA) metabolism in old nonstressed rats was significantly reduced in the medial frontal cortex, neostriatum, nucleus accumbens and hypothalamus, but not in the amygdala. The CER procedure, nevertheless, increased medial frontal cortical, nucleus accumbens and amygdaloid DA turnover in both the young and old rats. The young and old nonstressed rats did not evidence differences in norepinephrine (NE) and serotonin (5-HT) concentrations. However, stress resulted in a decrease in medial frontal cortical 5-hydroxyindoleacetic acid (5-HIAA) and hypothalamic 5-HT levels in old but not in young animals. These observations suggest age-related differences in the response of central NE and 5-HT systems to stress. Ether and the CER procedure led to exaggerated corticosterone responses in the old rats (17.5 and 22 month, respectively). Hippocampal type I but not type II corticosterone receptors were decreased by 47% in the 17.5-month-old rats. Thus, age-related changes in hippocampal corticosterone receptor types do not occur in unison, and the exacerbated corticosterone response to stress precedes the reported down-regulation of hippocampal type II corticosterone receptors in aged rats. Age-related changes were not observed in the concentrations of corticosterone receptors in other brain regions, or in the prolactin response to stress. The old rats, however, evidenced a reduction in the availability of the renin substrate, angiotensinogen, and in stress-induced renin secretion. Immune function was impaired in the old nonstressed rats, and further compromised by exposure to the CER procedure. In comparison to the young control rats, the old nonstressed rats showed an increased percentage of splenic large granular lymphocytes, reduced splenic natural killer cytotoxicity, and impaired Con-A-stimulated splenic T lymphocyte proliferation. Reductions in T splenic cell proliferation and natural killer cytotoxicity were observed in the young rats subjected to the CER paradigm, but not to the same extent as in the old rats. These observations indicate that aging male F344 rats evidence major alterations in basal central monoamine, endocrine and immune functions, and an increased sensitivity of these systems to stress.     

Metabolic mass, metabolic rate, caloric restriction, and aging in male Fischer 344 rats

Previous investigators have found the metabolic rate to be the same in calorically-restricted and ad-libitum fed rodents, and hence concluded that the Rate of Living Theory does not help explain the longer lifespan of the calorically-restricted (CR) animal. However, these previous instigators may not have used reliable estimates of metabolic mass in their calculations of metabolic rate. Hence the present study investigated the reliability of ten different estimates of metabolic mass (MM) in 21-month-old male Fischer 344 rats fed three different diets to yield a wide range of body compositions. Two criteria were used to rank each estimate of metabolic mass: strong correlation with daily caloric intake (DCI); and zero Y-intercept on the regression curve of DCI versus the MM. The combined weight of the heart, liver, kidneys and brain (OW) was found to be the best estimate of MM. Statistical analysis of the differences in metabolic rate in the three groups of rats showed that the significance of these differences depended on the estimate of MM used. OW yielded different results than did fat-free mass (FFM), body weight (BW), BW(0.75), and BW(0.67). Therefore, because previous investigators used FFM, BW, BW(0.75), or BW(0.67), rather than a more reliable estimate such as OW, their finding that metabolic rate was not different in the CR and ad-lib groups, and their conclusion that the Rate of Living Theory does not help explain the longer lifespan of the CR animal, are called into question.     

Spectrum of molecular changes during hepatocarcinogenesis induced by DEN and other chemicals in Fischer 344 male rats

Unlike other tissues such as breast, colon and renal cell carcinoma, it is not an easy task to single out any representative oncogene or tumor suppressor genes in the development of hepatocellular carcinoma (HCC), which play a pivotal role. To investigate putatively altered main pathways in HCC, F344 male rats were treated with a single injection of N-nitrosodiethylamine (DEN), followed by either twice/week injections of nodularin for 10 weeks or thioacetamide (TAA) in drinking water for 39 weeks. p53 expression was dramatic in both hepatocytes and mesenchymal cells after a single injection of DEN, however, PCR-SSCP assay could not detect any p53 mutation during the development of hepatocellular adenoma. The data indicate that wtp53 response was mostly for removal of damaged cells during the initiation of carcinogenesis. When treated with DEN-TAA, induction of gankyrin expression during hepatic fibrosis preceded the loss of pRB protein, accompanied with significant expressions of G1 phase cyclins and CDKs. Moreover, p16(INK4A) exon 1 was hypermethylated during the development of poorly differentiated HCCs. These changes would result in complete inactivation of the pRB regulatory pathway during hepatocarcinogenesis. Induction of TGF-beta1 expression with loss of its receptor expression occurred rapidly in the altered hepatocytes by DEN-nodularin treatment. CONCLUSION: Therefore, escape from TGF-beta1 induced apoptosis and severe degradation of pRB protein during the early stage of carcinogenesis can perform a symphony to proliferate and to transform the altered hepatocytes to tumor cells. Inactivation of p16(INK4A) and p53 genes at the later stage of carcinogenesis would endow HCC with malignancy, which is highly resistant to any therapeutic trials.     

An analysis of submandibular salivary gland function with desipramine and age in female NIA Fischer 344 rats

Dry mouth is one of the major side effects of cyclic antidepressants, which are still a dominating group of psychotherapeutic drugs used in the treatment of depression. In this study we analyzed the effects of 28 day tricyclic antidepressant administration and the reversibility of this treatment following a 15 day washout period on different parameters in submandibular gland function in aging rats. We postulated that desipramine would decrease gland function, accented with age, and delay recovery in senescent animals. In contrast to body weight, desipramine had no effect on glandular wet weight. While glandular DNA synthesis was changed with age and treatment, the concentration of total membrane and soluble proteins was not affected. Flow rate was significantly changed with age, but desipramine increased salivary flow in the youngest animals only. Neither age nor treatment influenced salivary protein concentrations, but the total amount of proteins secreted, revealed perturbation with age. SDS- polyacrylamide gel analysis revealed changes in protein expression with treatment and age. Desipramine decreased epidermal growth factor (EGF) levels in all age groups, but increased the secretion of peroxidase and lysozyme. Analysis of total RNA showed a pronounced decrease with age. These data indicate that desipramine has profound effects on submandibular salivary gland function.