Pathological characterization of male Wistar rats from the gerontology research center

Differences reported in the lifespan and aging of male Wistar rats maintained on diets containing fat with different fatty acid profiles (virgin olive, sunflower or fish oils) are not reflected by histopathological lesions found at death in central nervous and endocrine systems

The present study was designed to examine if dietary fat sources that have shown differences in lifespan and if some aging-related aspects can modulate the range of histopathologic changes in central nervous and endocrine systems that occur during the lifespan of Wistar rats. Moreover, it was attempted to gain insight into the relationship between longevity and the development of the different pathological changes, as well as possible interaction with diet. In order to achieve this, male Wistar rats were randomly assigned to three experimental groups fed semisynthetic and isoenergetic diets from weaning until death with different dietary fat sources, namely virgin olive, sunflower, or fish oil. An individual follow-up until death of each animal was performed. Incidence, severity, and burden of specific or group (i.e., neoplastic or non-neoplastic proliferative and non-proliferative) of lesions was calculated along with individual's disease and individual organ lesion burden. Most of the histopathological lesions found have been described in previous studies. Neoplasms, and in particular pituitary adenomas followed by brain tumors, were the most prevalent lesions found in the rats and the main cause of death involving both systems. Incidence of brain lesions was associated with age-at-death. Assayed dietary fats did not present differential effects on pathological changes occurring in endocrine and central nervous systems throughout rat lifespan.

Cause-of-Death Analysis in Rodent Aging Studies

In research studies using rats or mice, the cause of death is often not evaluated or reported. An analysis of the causes of death is particularly valuable for aging and carcinogenesis studies. Comparing causes of death among the study groups is often an important adjunct to the biochemical, molecular, clinical, and histopathologic findings. The methods for evaluating causes of death, contributing causes of death, and comorbidities have been suggested in several publications. Surprisingly, in important mouse aging studies, causes of death are often not reported. Cause-of-death assignment in preclinical rodent model aging research suffers from a lack of a standardized approach and an understanding of the value that it can add to longevity and interventional studies. While assigning single cause of death may facilitate data analysis, defining and publishing data on contributing causes (comorbidities) provides more information on associated underlying chronic conditions and health span in mouse models. This article reviews factors that affect determination of cause of death and the methods for evaluating causes of death and comorbidities. The proposed systematic pathology analysis includes assigning cause of death and comorbidities to define total disease burden. The combination of pathology with in vivo data will fully characterize the effect of tested interventions on multiple chronic diseases and health span of aging mice with improved translation to human aging and age-associated lesions.

Tyrosine kinase receptor alteration of renal vasoconstriction in rats is sex- and age-related

Male rat renal blood vessels undergo reduced contraction to norepinephrine with aging. There is a greater renal vascular impairment in male compared with female rats. We investigated specific tyrosine kinase receptor inhibition of renal interlobar artery responsiveness to phenylephrine in male and female rats at specifically designated ages. Vessels from young male rats contracted much less to phenylephrine when the vessels were pretreated with the tyrosine kinase inhibitors Lavendustin A, HNMPA-(AM)₃, or AG1478. Vessels from adult female rats pretreated with Lavendustin A showed no difference in contraction from control, but did demonstrate a slightly reduced contraction when pretreated with AG1478. Middle-aged male rat vessels treated with Lavendustin A demonstrated no inhibition, but the insulin and epidermal growth factor receptor (EGFR) antagonists both induced a decline in contraction. Vessels from aged male rats demonstrated no effect related to the 3 pretreatments. Middle-aged and aged female rats pretreated with any inhibitor demonstrated no inhibitor-dependent alterations. We conclude that maximum contraction of interlobar arteries from adult male rats is reduced when tyrosine kinase receptor activity is reduced. Female rats demonstrated much less inhibitor-related change of contraction.

Reduced alpha adrenergic mediated contraction of renal preglomerular blood vessels as a function of gender and aging

As human males age, a decline in baroreflex-mediated elevation of blood pressure occurs due, at least in part, to a reduction in alpha-1 adrenergic vasoconstrictor function. Alpha adrenergic constriction is mediated by guanosine triphosphate binding Protein (G Protein) coupled signaling pathways. Alpha-1 A/C, B, and D adrenergic receptor expressions, measured by GeneChip array, are not reduced during aging in renal blood vessels of male or female rats. Alpha-1 A GeneChip expression is greater, at all ages studied, in females than in males. Prazosin binding by alpha-1 adrenergic receptors is greater in young adult female rats than in young adult male rats; however, it is reduced with aging in both male and female rats. G alpha q GeneChip expression declines while expression of adrenergic receptor kinase (GRK2) and tyrosine phosphatases (TyrP) increase with aging in male rats. The declines in alpha-1 adrenergic receptor binding and G alpha q expression and also the increases in GRK2 and TyrP expression likely relate to the age-related decline of vasoconstriction in male rats. The information that the expression of alpha-1 A adrenergic receptors is greater in female rats and (GRK2) expression does not increase during aging could relate to the gender differences in vasoconstrictor function with aging. Gene therapy to ameliorate the age-related decline in renal function could possibly reduce the need for renal dialysis. Signaling pathways such as those reviewed herein may provide an outline of the molecular pathways needed to move toward successful renal gene therapy for aging individuals.

Decreased alpha-adrenergic constriction of renal preglomerular arteries occurs with age and is gender-specific in the rat

Age and/or gender appear to moderate alpha-adrenergic mediated constrictor mechanisms found in the interlobar arteries of the Munich Wistar rat. We have determined the extent of constriction to alpha-adrenergic receptor stimulation using norepinephrine, phenylephrine and A61603 (α1A-adrenergic receptor agonist) as a function of age and gender. Norepinephrine produced less constriction in male-derived arteries at ages greater than eight months as compared to the younger adult male (four to six months). The arteries derived from females did not demonstrate altered constriction until greater than 15 months of age. Similarly, arteries derived from the male demonstrated weaker constrictions to phenylephrine (10(-6) to 10(-3) M) at ages greater than eight months while arteries from females showed differences at greater than 15 months. In contrast, the effective concentration of norepinephrine to cause a 50% maximal constriction (EC50) was significantly less in the four to five-month-old male rats compared to the pooled data from older groups. Interestingly, four to five month old males had A61603 EC50 values similar to the 8 to 12-month and 15+ old females. These studies conclude that an age related loss of sympathetic α-adrenergic constriction of renal interlobar arteries is present in Munich Wistar rats. Furthermore, this loss, while similar along longitudinal aspects of age, is also different as a function of gender with the loss of α-adrenergic constrictor function delayed in the female when compared to the male.

Alpha 1 adrenergic receptor control of renal blood vessels during aging

Aging humans and rats have a reduced renal vascular constriction response to stress, change in posture, or exercise. In this study, renal interlobar arteries from 9- (intermediate age) to 15-month-old (aging) male Wistar rats constricted less to alpha-adrenergic agonists than those of 4-month-old (young adult) rats. The reduced contraction to A61603 (alpha 1 A agonist) was similar to that to norepinephrine and phenylephrine. Therefore, it appears that the reduction in constriction is primarily related to alpha 1 A receptor stimulation. GeneChip microarray hybridization analysis of the interlobar arteries with the RAE 230A GeneChip indicated that there were no significant differences in gene expression for alpha 1 A/C, 1B, or 1D receptors between 4-month-old (young adult) and 1-year-old (aging) male Wistar rats. Competitive binding experiments (prazosin) revealed that maximal binding (Bmax, fmol/mg protein) of the alpha 1 receptors of interlobar arteries was reduced 25% by 10 months of age and 50% by 18+ months of age. Alpha 1 receptor-induced arterial constriction and prazosin binding were both down-regulated. The loss of receptor-initiated constriction likely includes down-regulation of maximum agonist binding by alpha 1 adrenergic receptors.Key words: kidney, stress, blood flow, male vs. female, GeneChip array, prazosin.

Protein kinase B, P34cdc2 kinase, and p21 ras GTP-binding in kidneys of aging rats

Renal nephropathy present in male Wistar rats more than 13 months of age was reported as an indication that the rats were in renal failure. In this study, the renal tissue damage at 14 months of age in male Munich Wistar rats was similar to that reported for Wistar rats, indicating that Munich Wistar rats could be another model for study of kidney function in the aging rat. The usual renal response to injury involves increased cell division and/or reparative processes that involve tyrosine kinase activity (TyrK) and/or guanosine triphosphate-binding (G) protein signal trans-duction pathways. This study reveals the presence of renal tissue damage coinciding with significantly reduced activity of Ras, Akt, and p34cdc2 kinase, the signaling proteins that regulate cell division and/or growth, in renal cortical tissues of aging rats compared to young rats (P < 0.005, P < 0.005, and P< 0.001, respectively). These results suggest that proteins involved in signal transduction pathways associated with cell replication are downregulated in the aging kidney cortex at a time when renal cellular damage is also present.

Oral squamous cell carcinoma in ad libitum-fed and food-restricted Brown-Norway rats

A high incidence of oral squamous cell carcinoma was present in male and female Brown-Norway rats fed ad libitum or food-restricted dietary formulations. One hundred eight-nine rats were examined from 4 dietary treatment groups: male ad libitum, male food-restricted, female ad libitum, and female food-restricted. The ad libitum treatment groups for both males and females had significantly more cases of oral squamous cell carcinoma than cohort food-restricted groups. In ad libitum rats, 10 of 47 (21%) males and 15 of 47 (32%) females had oral squamous cell carcinoma, whereas only 4 of 47 (9%) males and 5 of 48 (10%) females in the food-restricted groups were similarly affected. The food-restricted rats lived significantly longer than ad libitum cohorts, so the higher incidence of squamous cell carcinoma was not dependent on extended lifespans. In addition to the dietary influence, a significant difference in oral squamous cell carcinoma incidence occurred between various familial lines. Family lines having representatives in both ad libitum and food-restricted groups had lower oral squamous cell carcinoma incidences in the food-restricted group whether comparing affected litters or individuals. Results suggest that the incidence of oral squamous cell carcinoma in our colony of Brown-Norway rats can be influenced by both the dietary treatment group and genetic predilection within certain pedigrees.

Influence of ovariectomy on bone metabolism in very old rats

Twenty-five 30-month-old Lou rats fed a diet (6 g/100 g BW/day) containing 0.9% Ca and 0.8% Pi were divided into five groups. Four groups were surgically ovariectomized. From day 2 until day 29 after ovariectomy, they were S.C. injected either with 17 beta estradiol (E2; 10 micrograms/kg BW/48 hours) or progesterone (P; 140 micrograms/kg BW/48 hours), or 17 beta estradiol + progesterone (E2P) at the same doses, or solvent alone (OVX). The fifth group was sham operated (SH) and injected with solvent. Urine was collected in metabolic cages from day 24 to 29 after ovx, and urinary pyridinoline (PYD) and deoxypyridinoline (DPD) excretion (markers of bone resorption) was measured by HPLC. All animals were killed 30 days after ovariectomy. Serum was then collected for measurement of osteocalcin (OC), alkaline phosphatase (ALP), parathyroid hormone (PTH), and calcitonin (CT). At necropsy, the success of ovariectomy was checked by marked atrophy of the uterine horns. Left and right femur were harvested for densitometric and mineral analysis, respectively. Ovariectomy had no significant effect upon plasma calcium and PTH concentrations. E2 or E2P treatment significantly increased plasma PTH and calcitonin concentrations. Plasma OC concentrations and ALP were not different in any of the groups. In contrast, urinary excretion of PYD and DPD was higher in OVX than in SH rats. Bone mineral density (BMD) of the distal femur was decreased by OVX, but was not different in the E2P and SH groups. A similar pattern was observed for the mineral or Ca content of whole femur. Thus, OVX decreased BMD and bone mineral content (BMC) in very old female rats. Plasma OC concentration and ALP activity failed to demonstrate any significant effect of OVX, whereas PYD and DPD were elevated. These results suggest that bone resorption is increased in OVX rats, even when supplemented with E2 or P alone. However, no significant difference was observed between SH and OVX rats treated with supplementation of both E2 and P. Thus, in very old rats, a combination of E2 and P is much more effective than E2 or P alone to prevent bone loss following ovariectomy.

Age-related changes in apolipoprotein A-I expression

To determine the age-related changes in apolipoprotein A-I (ApoA1) expression, male Fischer 344 rats at 4 (young), 12 (intermediate age), and 24-26 (aged) months of age were studied. Immunoblot analysis of plasma proteins indicated that 26-month-old rats (1.79 +/- 0.16 mg/ml) and 12-month-old rats (2.23 +/- 0.11 mg/ml) have significantly higher plasma ApoA1 concentrations compared to 4-month-old rats (1.14 +/- 0.15 mg/ml) P < 0.001. Hepatic ApoA1 mRNA was approx. 2-fold higher in aged rats compared to 12-month-old and 4-month-old rats. This increase in hepatic ApoA1 mRNA in aged rats was also reflected in the increased translation of ApoA1 mRNA in vitro. Reduced mRNA turnover may account for the increased hepatic ApoA1 mRNA content in 26-month-old rats, since the rate of ApoA1 gene transcription as measured with nuclear run off assays was significantly reduced with age. The ApoA1 synthesis in vivo, as measured by [14C]leucine incorporation at 30 min, was reduced in aged rats compared to young rats (170.5 +/- 10.2 vs. 253.9 +/- 7.7 cpm per liver) P < 0.001 probably as a result of changes related to cellular metabolism rather than an alteration inherent to the ApoA1 mRNA translatability. The age-related increase in plasma ApoA1 protein is probably secondary to reduced metabolic clearance rate of ApoA1 protein or is the result of increased intestinal synthesis of ApoA1.

Detection and quantitation by competitive PCR of an age-associated increase in a 4.8-kb deletion in rat mitochondrial DNA

Recent studies on human tissues have shown that the quantity of partially deleted mitochondrial DNA (mtDNA) increases with age. In this study, mtDNAs from the livers of young adult and old Wistar rats were analyzed by PCR. Evidence for partially deleted mtDNAs was found, with a 4834-bp deletion present in all animals and most easily detected in samples from senescent rats. The deletion breakpoint occurs at a 16-bp direct repeat present in the cytochrome oxidase I and ATPase 6 genes. This deletion in rats is similar in size and location to the 5.0-kb deletion observed in human mtDNA. The proportion of rat mtDNA with this 4.8-kb deletion was quantitated by a competitive PCR assay. The ratio of partially deleted mtDNA/total mtDNA in liver mtDNA from individual 6 month old rats ranged from 5 x 10(-6) to 3 x 10(-5), while the ratio in 24 month old rats ranged from 8 x 10(-4) to 5 x 10(-3), with a mean 100-fold increase with age. These increases are in the range observed for human mtDNA during aging. Thus senescent rats can be used as a model to study this type of mitochondrial DNA damage in aging. The method and reagents described should prove useful in studies of the mechanism(s) underlying deletions, their significance to the aging process, and testing of various compounds or interventions for their ability to slow the process.