Rats Of Different Age Groups Research Articles

Age-dependent variations of diastolic stiffness and collagen content in rat ventricular myocardium.

A parallel investigation on collagen content and diastolic mechanical properties has been performed on myocardial specimens isolated from male albino Wistar rats of different age groups (1-5 days, 10-20 days, 2 months, 8 months, 18 months, 24-26 months). Total water content, inulin-distribution space, protein concentration were determined together with hydroxyprolin content of the tissue. Mechanical properties of isolated papillary muscles were characterized in terms of static, dynamic, and plastic response to strain. During maturation (from birth to 2 months) the increase of collagen content is paralleled by an increase of static elasticity and by a reduction of plasticity. During maturity (2-8 months) and ageing (8-26 months) the collagen concentration in myocardial tissue still increases, but this change is associated to a reduction of the static components and to an increase of dynamic components of myocardial stiffness. A comparison between specimens from right and left ventricular myocardium indicates that a higher collagen content in the right ventricle is associated with a higher static elasticity.

DNA synthesis in rat heart cells after injury and the regeneration of myocardia

The regenerative responses of the myocardia of post-natal rats of different age groups (1, 2, 3 and 4 weeks old) to an injury made by a clinical electricator were studied. DNA synthesis and the ultrastructural organization of the cardiac myocytes of the injured myocardia were examined for an evaluation of the potential for regeneration of the developing myocardia. The maximum labeling index of cardiac myocytes was observed in 1-week-old rats showing 8% labeled myocytes 3 days after injury as opposed to 3.2, 2.2 and 0.2% indices in 2-, 3- and 4-week-old rats respectively, 3 days after injury. In subsequent days after injury the labeling indices declined considerably in all age group hearts, and attained values less than 1% labeled myocytes 30 days after injury with the lowest labeling index in the oldest age group heart. When DNA synthesis in uninjured myocardial tissue adjacent to the injured tissue was examined, it was found to be significantly lower than it was in the injured tissue. However, both injured and adjacent uninjured tissue attained a peak in the labeling indices 3 days after injury, with the exception of 3- and 4-week-old uninjured tissue. The overall incorporation of 3H-thymidine into the DNA of heart cells as revealed by scintillation counts showed that the rate of incorporation of the isotope in younger hearts was significantly higher than in the older hearts. Non-muscle cells contributed significantly to the rise of scintillation counts in hearts of all age groups. Ultrastructural analyses of 1- to 4-week-old hearts showed that 24 hr after injury, injured areas of myocardia were heavily crowded with macrophages that surrounded damaged myocytes. Later on, fibroblasts and other non-muscle cells predominated the injury sites along with fibrous connective tissue. Scattered regenerating cardiac myocytes were frequently observed in the injury sites of 1- and 2-week-old hearts 3 days after injury. Myocytes were rare in the corresponding regions of 3- and 4-week-old hearts. Instead abundant non-muscle cells and fibrous connective tissue were predominant. In the fourth and final week of this study, the repaired areas of myocardia in 1- and 2-week-old rats contained more myocytes than those of the 3- and 4-week-old rats, and the repaired zone of the 1-week-old heart contained more myocytes than the repaired areas of the other age groups. These findings suggest that the mammalian myocardia possess an age-dependent potential for regeneration that involves the healing of injury sites with contractile and connective tissues.

Effect of toluene exposure on the liver under different experimental conditions

The effect of exposure to toluene inhalation was studied in adult mice, rats, and rabbits, and, further, in rats of different age groups and rats subjected to partial hepatectomy or ligation of the common bile duct. It was found that (1) toluene has no substantial liver damaging effect on the mouse, rat, or rabbit; (2) induction of microsomal monooxygenase enzymes by toluene is almost completely independent of physiological changes affecting the functional-anatomical state of the liver (aging), of restriction of the functional capacity of the organ (partial hepatectomy), and of irreversible hepatic damage (bile duct ligation); (3) toluene does not in any way interfere with surgically induced hepatic damage. The consequences of surgical interventions, in turn, just like the age-dependent changes, do not modify the minimal ultrastructural damaging effect of toluene.

Myocardial kinetics and organ distribution of thallium-201 in two different age groups of rats.

Effects of aging were investigated on kinetics and distribution of 201 thallium (201TI) in isolated myocardial tissue and other organs of rats after injection in vivo of this radionuclide. Older rats showed a trend toward lesser organ uptake, but this was statistically significant only in kidneys, fat, and fur. Experimental outflow curves for 201TI from isolated myocardial wall segments revealed a sustained higher level of 201TI in the older rats throughout the outflow. Further analysis of the washout kinetics with a three-compartment model (extracellular, intracellular, and subcellular) showed a significant reduction of extracellular compartment and increase of subcellular compartment in older rats. The extracellular to overall intracellular ratio also decreased significantly in the older rats. The changes found for 201TI in extracellular and subcellular myocardial compartments in older rats at rest are also similar to those seen in myocardium of young rats after exercise. It is concluded that, although aging has effects on distribution of 201TI in myocardium, such effects are not likely to impair the quality of myocardial scintigraphy in older patient

Effect of protein malnutrition on the crosslinking of dermal collagen in aging

The effect of protein malnutrition on collagen crosslinking was studied in different age groups of rats. The percent of reversibility of neutral salt-soluble collagen gel and the susceptibility of insoluble collagen to denaturing agents and pronase decreased with aging. The electrophoretic pattern of neutral salt-soluble collagen on sodium dodecyl sulphate polyacrylamide gels showed a decrease of α 1 and α 2 subunits and an increase of β-components, resulting in a decrease of α/β ratio in aging. There was a significant decrease in the aldehyde content of neutral salt-soluble collagen during age. Protein deficiency was found to impair the crosslinking and the effect was greater in younger animals than in older ones.

Kindling in developing rats: variability of afterdischarge thresholds with age

In the kindling model, the occurrence of afterdischarges is necessary for the development of seizures. In this study, the afterdischarge thresholds of the amygdala were determined in rats of different age groups, beginning with 15-day-old suckling rats. Afterdischarges were triggered in 75% of the suckling rats and in all of the rats in the older age groups. The afterdischarge thresholds varied with age, being highest in the suckling group, lowest in the 35-day-old group and intermediate in the older groups. This variability of the thresholds did not correlate with the alterations in the catecholamine levels in the amygdala that occur during maturation. The failure of 25% of suckling rats to develop afterdischarges may explain why some suckling rats do not kindle.

The effect of hormones on the haemodynamics in animals of different age groups

The investigation was undertaken to study to effect of varying doses of epinephrine, vasopressin, insulin, thyroxin, estradiol-dipropionate on the haemodynamics and contractility of the myocardium of rats in different age groups, as well as the effect of epinephrine and vasopressin on coronary blood circulation in dogs of various age groups. The age group peculiarities of reactions to the hormones were compared with changes in their content in the blood of animals of different age groups. Upon administering small concentrations of the hormones in this study, more pronounced changes in haemodynamics and contractility of the myocardium were observed in senile animals. The administration of larger doses led to more pronounced changes in mature animals. During the process of aging, there is a decrease in the range of the reactions of the cardiovascular system to the action of hormones. In case of long term (14 days) administration of thyroxin, it was found that in senile animals the contractility of the heart was lower than that in short term (4 days) administration. In long term administration of thyroxin, it was found that in mature animals the index for the myocardium's contracting ability was more pronounced than in short term administration. Irregular changes in the concentrations of different hormones in the blood, changes in sensitivity and ability of the myocardium to respond to their action lead to changes in the hormonal regulation of the heart, and to the development of aging metabolic and functional changes.

Hydroxyproline excretion and collagen catabolism in rats of different age groups

Hydroxyproline as an index of collagen catabolism was studied in 432 urine samples collected from rats of different age groups at 4-hr intervals during the 24-hr period. The results showed statistically significant circadian rhythm in urinary hydroxyproline excretion with a peak between 2200 and 0200. The amount excreted is significantly more during the dark hours which can be correlated with the activity cycle. Total amount of excreted hydroxyproline decreases with age. The present results clearly show the importance of the determination of urinary hydroxyproline over a 24-hr period for clinical purposes.

Effect of thyroxine on the hepatic glycogen and glucose-6-phosphatase activity of developing rats.

The influence of exogenous thyroxine was studied on the hepatic glycogen content and glucose-6-phosphatase activity of rats of different age groups. The glycogen content and glucose-6-phosphatase activity were found to be decreased in the livers of 5, 15, 30 and 60-day-old rats after thyroxine treatment. In normal rats of 5, 15, 30 and 60-day-old, a gradual rise in both the hepatic glycogen content and glucose-6-phosphatase activity was noted as the age advanced from immature to adult.

Heart-rate responses and Hebb-Williams Maze performance in three different age groups of rats.

A study was carried out to examine heart-rate changes and changes in performance levels in Hebb-Williams maze in three different age groups of rats (21, 43, and 83 days old). Heart rate was recorded using a miniature FM radio transmitter. The rats were first exposed to 6 odd Hebb-Williams maze items and were retested 12 days later using 6 even test items. The main findings were: over-all the heart rate was significantly higher in the 21-day-old group and heart rate in this group decreased during the running of the maze while it increased in the other two groups. Heart-rate responses increased as a function of trials in all the groups and increased most sharply for the 21-day-old group. On retest a significant over-all decrease occurred in the heart-rate responses. The short-term reliability of heart rate was quite high for all the age groups. The 21-day-old group rats made significantly fewer errors in the Hebb-Williams maze when compared with the two older groups but the test-retest reliability of the Hebb-Williams maze scores was very low in the 21-day group relative to the other two. The results are discussed in terms of response inhibition and changes in drive level as a function of age. Questions are also raised concerning the validity of the Hebb-Williams maze test as a measure of problem-solving behavior.

Studies on age-related changes in the metabolism of eosin in the rat

Male rats of different age groups maintained normally on laboratory chow were injected with eosin (2,4,5,7-tetrabromo-11-carboxyfluorescein) after which the biliary excretion of the dye was studied. In 3 age groups below 42 weeks, the dye was excreted as 2 compounds which were identified by thin-layer chromatography as unchanged eosin ( R f 0.90–0.91) contributing about 80–90% and one conjugated compound of R f 0.43–0.47 (14–19%) which was shown to be a glucuronide. Eosin metabolites could not be traced in 30 and 42 week-old rats. This finding is discussed in relation to: (i) age and enzymic activity, and (ii) bio-activated metabolites of this dye which may induce biochemical or toxicological and carcinogenic lesions.

Influence of age and milk diet on cadmium absorption from the gut

Cadmium absorption was studied in different age groups of rats (1, 3, 6, and 52 weeks) fed milk or standard rat diet by determining the whole body retention of orally applied 115mCdCl 2. The whole body retention curves determined over 2 weeks after the 115mCd administration showed highest values in newborn rats. All animals on the milk diet had higher retention values than controls. Within each diet group the retention curves declined with age and the lowest values were obtained in the oldest group of animals. These results indicate that age and diet independently influence cadmium absorption and that the highest values in the newborn most probably result from a combined effect of age and milk diet.

Experimental analysis of development of cardiac insufficiency in old age

The investigation was undertaken to study to effect of varying doses of epinephrine, vasopressin, insulin, thyroxin, estradiol-dipropionate on the haemodynamics and contractility of the myocardium of rats in different age groups, as well as the effect of epinephrine and vasopressin on coronary blood circulation in dogs of various age groups. The age group peculiarities of reactions to the hormones were compared with changes in their content in the blood of animals of different age groups.Upon administering small concentrations of the hormones in this study, more pronounced changes in haemodynamics and contractility of the myocardium were observed in senile animals. The administration of larger doses led to more pronounced changes in mature animals. During the process of aging, there is a decrease in the range of the reactions of the cardiovascular system to the action of hormones.In case of long term (14 days) administration of thyroxin, it was found that in senile animals the contractility of the heart was lower than that in short term (4 days) administration. In long term administration of thyroxin, it was found that in mature animals the index for the myocardium's contracting ability was more pronounced than in short term administration.Irregular changes in the concentrations of different hormones in the blood, changes in sensitivity and ability of the myocardium to respond to their action lead to changes in the hormonal regulation of the heart, and to the development of aging metabolic and functional changes.

Glycoprotein biosynthesis in the developing rat brain III. Are glycoprotein glycosyl transferases present in synaptosomes?

Synaptosomes were prepared from brains of rats of different age groups and from embryonic chick brains and glycoprotein glycosyl transferase activities of these preparations were compared. It was observed that the glycosyl transferase activities were always associated with the presence of membrane-bound polysomes in these fractions. Furthermore since synaptosomal fractions in which the polysomal contamination was minimal had little or no glycosyl transferase activity, it is concluded that the transferase activity which has been ascribed by other workers to the synaptosomal fraction, can in fact be traced to the presence of membrane-bound polysomes.

Hormone-sensitive lipolytic activity of the aorta of different age groups of rats

The lipomobilizing power of the aorta was investigated in animals of various ages (3, 6, 12, 18 and 24 months old). Lipomobilization was followed up in vivo after the intraperitoneal injection of adrenalin, by means of FFA values in the aorta. An in vivo experiment after the intraperitoneal injection of adrenalin was carried out in animals adapted to the chronic administration of ACTH-Corticot rophin Spofa. The FFA release from the aorta of old animals was found to be decreased. A decreased FFA response in the aorta was observed in animals adapted to repeated ACTH administration, In in vivo experiments after incubation with adrenalin less FFA were liberated into the medium from the aorta of ageing and old animals. The age of the animal also influenced the total aortic triglyceride content in relation to its nitrogen content it increased with age.

Propensity for paradoxical sleep following deprivation in rats of different age groups

The propensity for paradoxical sleep (PS) during different maturational stages was investigated by depriving adolescent and adult rats of PS for 72 h. Despite more PS under baseline conditions, adolescent rats did not have significantly more PS than did older animals on two postdeprivation sessions. However, before any meaningful conclusion can be drawn about the differential need for PS following deprivation by different age groups, such variables as period of deprivation and stage of maturation must be considered with great care.

Uterine metabolism changes during gestation in rats of different age groups.

SummaryChange in the TTC reduction rate of uterine tissue during gestation in varying aged rats was determined. Old females (300-330 days) and young females (60-80 days) showed an increase in uterine TTC reduction rate at day 12 post-breeding, whereas females 120-150 days old did not. Fetal loss was greater in the 300-330-day-old and the 60-80-day-old females than in the 120-150-day-old females. The stage of gestation when increased fetal losses occurred appeared to coincide with the rise in uterine TTC reduction rate at day 12 post-breeding.

The dstribution of calcium-47 in the rat.

1. Plasma specific activities were measured at various times after the intravenous injection of calcium-47 in four different age groups of rats.2. The data may be represented as two power functions. The change in power function occurs at a set time which is significantly different in three of the age groups.3. Various bones, muscle and skin all show different uptakes of the calcium-47 and the change in the power function of the plasma data probably represents an equilibrium of the soft tissue calcium.

Toxicity of pesticides in young versus adult rats

The acute oral toxicity of the pesticides malathion, dieldrin and DDT has been studied in rats of different age groups. The newborn rats were much more sensitive than the pre-weaning and adult rats to malathion, but they were less sensitive to DDT and dieldrin. In fact, an LD 50 could not be determined for DDT in newborn rats, since no death occurred at doses up to 4 g/kg. The pre-weaning rats were intermediate between newborn and adult rats in their sensitivity to malathion and DDT, but appeared to be slightly more susceptible than the adult rats to dieldrin. In adult rats, the toxicity of these 3 pesticides was reduced when they were given in divided doses over a period of 4 days, whereas in the pre-weaning rats, their toxicity was augmented by this procedure.

The development of the motor innervation of different parts of the gastric musculature in the rat

The vagi were divided subdiaphragmatically in rats of different age groups, from two weeks upwards. Different effects were observed on contraction and on chemoreception of the gastric musculature. Vagal fibers exert different functions in different regions of the stomach, as shown by their different regulatory effects. In the adult rat, the inhibitory effect of epinephrine was increased or reversed after vagotomy. In rats aged 1–2 months, the inhibitory effect of epinephrine on the muscles was less pronounced, or entirely absent.