Mitochondrial respiration and triiodothyronine concentration in liver from postpubertal and adult rats.

The purpose of this study was to investigate the decline in rat liver mitochondria respiration found in adult rats compared to younger ones, and to find a link between this respiratory impairment and a tissue hypothyroidism state. To this end, hepatic concentration and serum levels of triiodothyronine were measured in postpubertal rats (60 days old) and adult rats (180 days old). In addition, in these rats we measured oxidative phosphorylation in homogenate together with coupled and uncoupled respiration in isolated mitochondria using succinate or durohydroquinone as substrate. We found that mitochondria from adult rats consumed less oxygen compared to younger rats due to lower electron transport chain and phosphorylating system activity. In addition, we found that in state 4 condition, mitochondria from adult rats consumed less oxygen than mitochondria from young rats. Finally, we found a decrease in liver triiodothyronine concentration in adult rats. In conclusion, the results of this study show that hepatic mitochondria in adult rats have a decreased ATP synthesis capacity and proton permeability, both consistent with the tissue hypothyroidism found in the liver of adult rats.     

Differences in the accessibility of the beta-adrenergic receptor in isolated hepatocytes from foetal and adult rats.

Beta-receptor number (measured by [3H]-CGP 12 177 binding) and beta-adrenergic response (measured by isoproterenol stimulated glucose liberation and isoproterenol stimulated adenylate cyclase activity) were compared in hepatocytes isolated from foetal (on day 22 of gestation), adult female and adult male rats. Beta-receptor numbers in crude membrane preparations of hepatocytes from adult female and adult male rats were found to be nearly equal (15.5 and 15.1 fmol/mg), but in crude membrane preparations of foetal rats beta-adrenergic receptor number was significantly higher (34.3 fmol/mg). Determination of number of beta-adrenergic surface receptors of intact hepatocytes showed relative high values in foetal rats (about 22,000/cell) and adult female rats (about 20,000/cell), but in male rats the number was less (about 6500/cell). Glucose liberation was stimulated by isoproterenol to the same extent in hepatocytes isolated from adult female and foetal rats (about 150% over basal), whereas no effect was found in hepatocytes isolated from adult male rats. Dose-response curves showed that in foetal rat hepatocytes glucose release was already increased by 10(-8) M isoproterenol, whereas in female rat hepatocytes at least 10(-6) M isoproterenol was required. Adenylate cyclase was stimulated by isoproterenol in lysates of hepatocytes from adult female rats by about 180% and from foetal rats by about 250%. No effects were observed using lysates of hepatocytes from adult male rats. We interpret the observed differences of beta-adrenergic responses between adult female and male rats as being primarily caused by different accessibility of the beta-receptor to the beta-agonist isoproterenol in intact hepatocytes.(ABSTRACT TRUNCATED AT 250 WORDS)     

Taurine transport across the small intestine of adult and suckling rats

1. Taurine accumulation in intestinal cells of adult and suckling rats reached steady-state after 60 min with an In/Out ratio of 1.46 and 4.66 in the adult and suckling rats respectively. 2. The accumulative capacity of the intestinal strips isolated from suckling rats is almost four times higher than that of adult rats. 3. The steady-state uptake of taurine by the adult and suckling rats intestinal cells is saturable, sodium-dependent and inhibited by ouabain. 4. The calculated Vmax of the mediated component of the steady-state uptake in the suckling rats is three times greater than that of the adult rats, and the affinity is seven fold greater in the suckling as compared to the adult. 5. Taurine influx across the mucosal membrane in the suckling rat is significantly greater than that of the control adult.     

Salt intake and intestinal dopaminergic activity in adult and old Fischer 344 rats

We have earlier shown that the renal dopaminergic system failed to respond to high salt (HS) intake in old (24-month-old) Fisher 344 rats (Hypertension 1999;34:666-672). In the present study, intestinal Na+,K+-ATPase activity and intestinal dopaminergic tonus were evaluated in adult and old Fischer 344 rats during normal salt (NS) and HS intake. Basal intestinal Na+,K+-ATPase activity (nmol Pi/mg protein/min) in adult rats (142+/-6) was higher than in old Fischer 344 rats (105+/-7). HS intake reduced intestinal Na+,K+-ATPase activity by 20% (P<0.05) in adult, but not in old rats. Dopamine (1 microM) failed to inhibit intestinal Na+,K+-ATPase activity in both adult and old Fischer 344 rats (NS and HS diets). In adult animals, co-incubation of pertussis toxin with dopamine (1 microM) produced a significant inhibitory effect in the intestinal Na+,K+-ATPase activity. L-DOPA and dopamine tissue levels in the intestinal mucosa of adult rats were higher (45+/-9 and 38+/-4 pmol/g) than those in old rats (27+/-9 and 14+/-1 pmol/g). HS diet did not change L-DOPA and DA levels in both adult and old rats. DA/L-DOPA tissue ratios, an indirect measure of dopamine synthesis, were higher in old (1.1+/-0.2) than in adult rats (0.6+/-0.1). Aromatic L-amino acid decarboxylase (AADC) activity in the intestinal mucosa of old rats was higher than in adult rats. HS diet increased the AADC activity in adult rats, but not in old rats. It is concluded that intestinal dopaminergic tonus in old Fisher 344 rats is higher than in adult rats and is accompanied by lower basal intestinal Na+,K+-ATPase activity. In old rats, HS diet failed to alter the intestinal dopaminergic tonus or Na+,K+-ATPase activity, whereas in adult rats increases in AADC activity were accompanied by decreases in Na+,K+-ATPase activity. The association between salt intake, increased dopamine formation and inhibition of Na+,K+-ATPase at the intestinal level was not as straightforward as that described in renal tissues.     

Sex-differentiated enzyme levels and oestrogen uptake in adult rats treated neonatally with tamoxifen or CI-628

Serum cholinesterase, hepatic histidase and monoamine oxidase activity levels are higher in adult female rats than in adult male rats. Exposure of neonatal rats to antioestrogen (tamoxifen or CI-628) resulted in increased serum cholinesterase in adult females only and no effect on hepatic histidase and monoamine oxidase in both sexes. Neonatal tamoxifen or CI-628 treatment resulted in reduced body weights in adult male rats and reduced uterine wet weights in adult female rats. Circulating oestrogen levels measured in adult female rats treated neonatally with tamoxifen were not significantly different from controls. Specific oestrogen uptake in the brain of adult male and female rats was found to be higher in the pituitary than in the preoptic-anterior hypothalamic area and the median eminence-basal hypothalamus than in the cerebral cortex. There was higher uptake of [3H]oestradiol-17 beta in male pituitaries than in female pituitaries. No other sex-difference was observed. Neonatal tamoxifen treatment did not alter the capacity of these brain tissues to take up oestrogen. It is suggested that neonatal antioestrogen exposure has altered the endocrine expression of serum cholinesterase in adult female rats by interfering with normal imprinting mechanisms.     

Adult rats prenatally exposed to ethanol have increased gluconeogenesis and impaired insulin response of hepatic gluconeogenic genes.

Rat offspring exposed to ethanol (EtOH rats) during pregnancy are insulin resistant, but it is unknown whether they have increased gluconeogenesis. To address this issue, we determined blood glucose and liver gluconeogenic genes, proteins, and enzyme activities before and after insulin administration in juvenile and adult EtOH rats and submitted adult EtOH rats to a pyruvate challenge. In juvenile rats, basal glucose; peroxisome proliferator-activated receptor-coactivator-1alpha protein and mRNA; and phosphoenolpyruvate carboxykinase enzyme activity, protein, and mRNA were similar between groups. After insulin injection, these parameters failed to decrease in EtOH rats, but glucose decreased by 30% and gluconeogenic enzymes, proteins, and mRNAs decreased by 50-70% in control rats. In adult offspring, basal peroxisome proliferator-activated receptor-coactivator-1alpha protein and mRNA levels were 40-80% higher in EtOH rats than in controls. Similarly, basal phosphoenolpyruvate carboxykinase activity, protein, and mRNA were approximately 1.8-fold greater in EtOH rats than in controls. These parameters decreased by approximately 50% after insulin injection in control rats, but they remained unchanged in EtOH rats. After insulin injection in the adult rats, glucose decreased by 60% in controls but did not decrease significantly in EtOH rats. A subset of adult EtOH rats had fasting hyperglycemia and an exaggerated glycemic response to pyruvate compared with controls. The data indicate that, after prenatal EtOH exposure, the expression of gluconeogenic genes is exaggerated in adult rat offspring and is insulin resistant in both juvenile and adult rats, explaining increased gluconeogenesis. These alterations persist through adulthood and may contribute to the pathogenesis of Type 2 diabetes after exposure to EtOH in utero.     

The effects of acetylsalicylic acid on phosphoenolpyruvate carboxykinase activity and acinar heterotopy in livers from juvenile and adult rats

Summary Male and female juvenile as well as adult rats were treated with acetylsalicilic acid in order to examine the effect of the drug on over-all activity and activity distribution of phosphoenolpyruvate carboxykinase (PEPCK) in the liver acinus. Upon administration of acetylsalicilic acid PEPCK activity increased in juvenile males and adult females, but was reduced in juvenile females and adult males. The periportal-perivenous activity gradient along the sinusoidal length, which is flatter in untreated juvenile rats compared to the livers of adult rats, was distinctly steepened by acetylsalicilic acid treatment. Acetylsalicilic acid did not affect the gradient in adult rats.     

The effects of acetylsalicylic acid on phosphoenolpyruvate carboxykinase activity and acinar heterotopy in livers from juvenile and adult rats

Male and female juvenile as well as adult rats were treated with acetylsalicylic acid in order to examine the effect of the drug on over-all activity and activity distribution of phosphoenolpyruvate carboxykinase (PEPCK) in the liver acinus. Upon administration of acetylsalicylic acid PEPCK activity increased in juvenile males and adult females, but was reduced in juvenile females and adult males. The periportal-perivenous activity gradient along the sinusoidal length, which is flatter in untreated juvenile rats compared to the livers of adult rats, was distinctly steepened by acetylsalicylic acid treatment. Acetylsalicylic acid did not affect the gradient in adult rats.     

Induction of acetylcholinesterase by 17- estradiol in the brain of rats of various ages

The induction of acetylcholinesterase (AChE) was studied in the cerebral hemisphere and cerebellum of immature (9-), adult (29-) and old (65-week) female rats. The specific activity of AChE of the cerebral hemisphere of normal rats is highest at 9 weeks and decreases thereafter. There is no such change in the cerebellum. Ovariectomy decreases its activity in the cerebral hemisphere of adult, and cerebellum of immature and adult rats, but not of old rats. Administration of estradiol to ovariectomized rats increases the activity in the cerebral hemisphere and cerebellum of immature and adult rats but not of old rats. The magnitude of stimulation, which is actinomycin D-sensitive, is highest in immature rats.     

Blood–Brain Transfer of Glucose and Glucose Analogs in Newborn Rats

Little is known of the selectivity of the blood-brain barrier at birth. Hexoses are transported through the barrier by a facilitating mechanism. To study the capacity of this mechanism to distinguish between analogs of D-glucose, we compared the transport of fluorodeoxyglucose, deoxyglucose, glucose, methylglucose, mannose, galactose, mannitol, and iodoantipyrine across the cerebral capillary endothelium in newborn Wistar rats. Cerebral blood flow, glucose consumption, and the blood-brain permeabilities of the hexoses were 25-50% of the adult values but the ratios between the permeabilities of the individual hexoses were similar to the ratios observed in adult rats. The mannitol clearance into brain was considerably higher than in adult rats (about 10-fold), indicating a higher endothelial permeability to small polar nonelectrolytes. The brain water content was higher in newborn than in adult rats and was associated with a higher steady-state distribution of labeled methylglucose between brain and blood. Hexose concentrations were determined relative to whole blood because the apparent erythrocyte membrane permeability to glucose was as high as in humans and thus considerably higher than in adult rats. The half-saturation concentration of glucose transport across the blood-brain barrier was considerably higher than in adult rats, about three-fold, suggesting that net blood-brain glucose transfer is less sensitive to blood glucose fluctuation in newborn than in adult rats.     

Increased choline acetyltransferase activity by Chinese herbal medicine Sho-saiko-to-go-keishi-ka-shakuyaku-to in aged rat brain

The effect of a Chinese herbal medicine Sho-saiko-to-go-keishi-ka-shakuyaku-to (TJ-960) on the brain choline acetyltransferase (CAT) activity was studied in adult (3.5 months of age) and aged (24 months of age) rats. After oral administration of 5% TJ-960 solution for 3 months, CAT activity in the hippocampus, pons-medulla oblongata and striatum of aged rats was significantly lower than that of adult rats. CAT activity in the cerebellum, however, was significantly higher in the aged rats, as compared to the adult rats. TJ-960 significantly increased CAT activity in the hippocampus and striatum of aged rats, but did not affect the activity of the enzyme in the adult rat brain.     

The influence of sialoadenectomy, thymectomy and starvation on liver glycogen in the rat

Hepatic glycogen was assayed in young and adult rats subjected to sialoadenectomy and/or thymectomy and starvation. Sialoadenectomy in young, but not in adult rats caused the rats to stop feeding. In young, but not in adult sialoadenectomized and starved rats the glycogen level was notably higher than in unoperated and starved rats, indicating active participation of salivary glucagon in immature animals in hepatic glycogenolysis under conditions of starvation. Simultaneous sialoadenectomy and thymectomy caused glycogen depletion in the liver of young rats in spite of the absence of the salivary glands. Acceleration of glycogenolysis in these rats was not due to thymectomy, being probably a result of excessive secretion of adrenal catecholamines.     

Adaptive responses of 25-hydroxyvitamin D3 1-alpha hydroxylase expression to dietary phosphate restriction in young and adult rats

Regulation of vitamin D metabolism alters with age. The present study is undertaken to investigate if the loss of renal 1,25-dihydroxyvitamin D(3) (1,25(OH)(2)D(3)) production in response to dietary phosphate (P) restriction in adult rats is due to an alteration in the renal expression of 25-hydroxyvitamin D(3) 1-alpha hydroxylase (1-OHase). Young (4-6 weeks old) and adult (12-14 weeks old) male Sprague Dawley rats were fed either normal P (NPD) or low P diet (LPD) for 0-5 days. Basal expression of 1-OHase protein was higher in adult rats. Young rats, but not adult rats, significantly increased 1-OHase protein and mRNA expressions in response to LPD in a time-dependent manner. To determine if the stability of renal 1-OHase protein changes with LPD feeding, young and adult rats fed either NPD or LPD for 5 days were injected intravenously with cycloheximide (CHX), a protein synthesis inhibitor. CHX decreased 1-OHase protein expression in young rats fed NPD. However, CHX did not alter 1-OHase protein expression in young rats fed LPD nor in adult rats fed either diet. The results indicate that the stability of renal 1-OHase protein increased with age and that LPD increased its stability only in young rats.     

The composition and fluidity of adipocyte membranes prepared from young and adult rats

Membranes from adipocytes of adult and young rats have been compared. Phospholipid fatty acids from adult rats were more saturated than those from young rats. This difference was associated with a decreased fluidity in the membranes of the adult rats, which was inferred from measurements of fluorescence polarisation of the fluorescent probe, 1,6-diphenylhexa-1,3,5-triene.     

Kin discrimination in prepubescent and adult Long-Evans rats

The present study investigated the preference of prepubescent and adult rats for an unrelated conspecific over a closely related conspecific (e.g., father, mother). Preference was measured by the amount of time spent in the vicinity of the stimulus animals as well as who was visited first. To prevent mating behavior, stimulus animals were housed behind wire-mesh. Experiment 1 determined if adult female offspring prefer an unrelated, unfamiliar adult male or their father. The preference of adult female rats was independent of kinship. Experiment 2 evaluated the preference of prepubescent female and male offspring for an unrelated, unfamiliar adult male or their father. The preference of prepubescent female and male rats was also independent of kinship. Experiment 3 evaluated the preference of adult male offspring for an unrelated, unfamiliar adult female or their mother. The preference of adult male rats was independent of kinship. In summary, prepubescent and adult rats do not demonstrate preference for kin vs. non-kin (as measured by time spent near stimulus animals or who was visited first). Although kin recognition provides a mechanism for inbreeding avoidance (Wilson, 1987), in the present study adult rats show no evidence of inbreeding avoidance.     

Rhythmic variations in acid phosphatase activity in the liver of newborn rats

The rhythm of acid phosphatase activity in liver homogenates of newborn rats (aged about 14 days) was compared with a similar rhythm in adult rats (aged 4.5 months). Serial chromatographic investigations demonstrating isoenzyme patterns demonstrated age-related changes of this rhythm connected with the synthesis of the enzyme in newborn rats. The averaged activity of the enzyme in the liver homogenates of newborn rats was about 4 times lower than in adult rats. The maximal values of total enzyme activity of both isoenzymes after chromatographic separation in newborn rats were shifted by about 7 hours in relation to adult animals. Similar changes were observed in the case of the greatest maximal values of the activity ratios--subunit: both isoenzymes, and isoenzyme II: isoenzyme I. In adult rats these maximal values appeared during the night hours and in newborn rats during the day.     

Aging Contributes to Inflammation in Upper Extremity Tendons and Declines in Forelimb Agility in a Rat Model of Upper Extremity Overuse

We sought to determine if tendon inflammatory and histopathological responses increase in aged rats compared to young rats performing a voluntary upper extremity repetitive task, and if these changes are associated with motor declines. Ninety-six female Sprague-Dawley rats were used in the rat model of upper extremity overuse: 67 aged and 29 young adult rats. After a training period of 4 weeks, task rats performed a voluntary high repetition low force (HRLF) handle-pulling task for 2 hrs/day, 3 days/wk for up to 12 weeks. Upper extremity motor function was assessed, as were inflammatory and histomorphological changes in flexor digitorum and supraspinatus tendons. The percentage of successful reaches improved in young adult HRLF rats, but not in aged HRLF rats. Forelimb agility decreased transiently in young adult HRLF rats, but persistently in aged HRLF rats. HRLF task performance for 12 weeks lead to increased IL-1beta and IL-6 in flexor digitorum tendons of aged HRLF rats, compared to aged normal control (NC) as well as young adult HRLF rats. In contrast, TNF-alpha increased more in flexor digitorum tendons of young adult 12-week HRLF rats than in aged HRLF rats. Vascularity and collagen fibril organization were not affected by task performance in flexor digitorum tendons of either age group, although cellularity increased in both. By week 12 of HRLF task performance, vascularity and cellularity increased in the supraspinatus tendons of only aged rats. The increased cellularity was due to increased macrophages and connective tissue growth factor (CTGF)-immunoreactive fibroblasts in the peritendon. In conclusion, aged rat tendons were overall more affected by the HRLF task than young adult tendons, particularly supraspinatus tendons. Greater inflammatory changes in aged HRLF rat tendons were observed, increases associated temporally with decreased forelimb agility and lack of improvement in task success.     

Different sensitivity of PPARalpha gene expression to nutritional changes in liver of suckling and adult rats

The amount of peroxisome proliferator-activated receptor-alpha (PPARalpha) protein was markedly augmented in the liver of suckling rats compared to adult rats. This different PPARalpha abundance was used to study the sensitivity to nutritional changes in the expression and activity of this receptor. Thus, 10-day-old and adult rats were orally given either glucose, Intralipid or a combination of both diets, and liver mRNA levels of PPARalpha and the PPAR related genes, acyl-CoA oxidase (ACO) and phosphoenolpyruvate carboxykinase (PEPCK), and plasma metabolites were measured. In neonates, the expression of PPARalpha and ACO was seen to increase when the level of FFA in plasma was also high, unless an elevated level of insulin was also present. However, this fatty acid-induced effect was not detected in adult rats. On the contrary, the hepatic expression of PEPCK was modulated by the nutritional changes similarly in both neonates and adult rats. Thus, it may be concluded that the expression of the PPARalpha gene in adult rats seems to be less sensitive to nutritional changes than in neonates.     

DNA-polymerase activity of the liver of adult and old rats

The DNA-polymerase activity was determined in the cytosol of the intact and regenerating liver of adult and old rats under conditions of free passage of enzymes from nuclei and mitochondria. The DNA-polymerase activity of the intact liver is significantly increased in adult rats. The regeneration results in about 2-fold and 10-fold increase of the activity in the liver of adult and old rats, respectively. As a result, the DNA-polymerase activity in the regenerating liver of old rats significantly increased as compared to that of adult rats. The revealed age-related changes in the DNA-polymerase activity of the liver do not correlate with the decrease in the replication rate in the process of aging.