Effects of aging and endotoxin on hepatic glucocorticoid action and glucose metabolism in mice

Influence of endurance training on the age-related decline in hepatic glyconeogenesis

Hepatic gluconeogenic and glyconeogenic capabilities were investigated in Fischer 344 rat livers (ages 7, 15 and 25 months; n = 66) to determine if endurance training affected age related decrements in these hepatic functions. Animals were trained 1 h/day, 5 days/week for 10 weeks at treadmill speeds of 75% of age-specific maximal capacity. After training, rats were injected (300 mg/kg) with a known gluconeogenic inhibitor, 3-mercaptopicolinic acid (MPA). Two endurance tests were performed to help assess the contribution of gluconeogenesis to exercise performance, an initial test 4 days prior to injection and a final test immediately post-injection. MPA significantly (P < 0.05) reduced running times in all trained groups compared to their control test: 89%, 81%, and 51% in the young, middle-aged, and old, respectively. MPA reduced running times in the untrained animals 19%, 11%, and 8%, respectively. Three days after the last exercise bout, the animals were anesthetized and liver sections were sliced and incubated in [14C]lactic acid or [14C]fructose. An age-related decline was found in [14C]lactate incorporation (middle-aged decreases 66%, old decreases 54%) and in [14C]fructose incorporation (middle-aged decreases 51%, old decreases 48%) into glycogen. Differences existed in lactate incorporation in trained compared to untrained animals for the young, middle-aged, and old groups: 150.1 +/- 11.3 vs. 102.1 +/- 10.0; 75.3 +/- 6.2 vs. 34.9 +/- 6.4; and 69.3 +/- 14.9 vs. 47.0 +/- 4.7 nmol/g/h, respectively. No differences were found with training in any of the age groups for fructose. Phosphoenolpyruvate carboxykinase (PEPCK) activity and messenger RNA (mRNA) were significantly reduced in the old compared to the young rats (decreases 64% and decreases 58%, respectively). No training effects were found for either PEPCK activity or mRNA for any age group. These results suggest that hepatic gluconeogenic and glyconeogenic capabilities declined with age. Training had an effect in attenuating the glyconeogenic decline but had a minimal effect in offsetting the age-related decline in PEPCK.

Lipopolysaccharide-tumor necrosis factor-glucocorticoid interactions during cecal ligation and puncture-induced sepsis in mature versus senescent mice

Previous work in our laboratory demonstrated increased sensitivity of senescent (24-month-old) mice to cecal ligation and puncture (CLP) sepsis compared with that of mature (12-month-old) mice. In this study the median lethal dose of the strain of Escherichia coli most frequently isolated during CLP sepsis was determined. No significant age-associated difference in the mean lethal dose or the mean survival time was noted; however, sham surgery before injection of E. coli decreased the mean lethal dose by at least 100-fold. With surgical manipulation, the average time to death after bacterial injection simulated more closely that observed after CLP surgery. Host responses to CLP sepsis were investigated by measuring the levels of corticosterone, glucose, and tumor necrosis factor (TNF) in the sera of mature and senescent mice at 2-h intervals after surgery. Corticosterone levels increased gradually during the course of sepsis in mature mice; however, senescent mice demonstrated a pronounced elevation in hormone levels at 2 and 4 h after surgery. At subsequent sampling intervals the corticosterone levels remained elevated, although they were similar for both ages. At all sampling intervals, the glucose levels in serum were lower in senescent mice than in mature mice. Pronounced hypoglycemia (less than 80 mg/dl) was observed in senescent mice at 8 h postsurgery. TNF was detected in serum within a narrow time frame in both age groups at 6, 8, and 10 h postsurgery. Although elevated TNF levels in serum were not seen in every mouse in each group (approximately 50%), the data hinted that senescent animals produced larger quantities of TNF during CLP sepsis than did mature animals. E. coli lipopolysaccharide (1 mg/kg) was injected intraperitoneally, and the TNF levels in serum and peritoneal lavage fluid were measured at 30, 60, and 90 min. Senescent mice demonstrated a level of TNF in serum at 90 min after lipopolysaccharide treatment that was 20-fold higher than that of mature mice (299,877 pg/ml versus 15,594 pg/ml). The amount of TNF produced locally in the peritoneum was also substantially higher in senescent mice than in mature animals (1,716 pg/ml versus 776 pg/ml). The increased production of TNF in senescent animals, despite elevated circulating corticosterone levels, suggested an age-related defect in glucocorticoid-directed downregulation of TNF production. This was confirmed in lipopolysaccharide-treated animals given exogenous dexamethasone.(ABSTRACT TRUNCATED AT 400 WORDS)

Mortality and bacteriology of sepsis following cecal ligation and puncture in aged mice

Epidemiologic data suggest that elderly adults are more susceptible to invasive bacterial infection by indigenous gut flora than are younger adults. The purpose of this investigation was to characterize a murine model of clinically encountered peritonitis in the aged. We subjected three different age groups (young, 16 weeks; mature, 12 months; senescent, 24 months) of C57BL/6NNia mice to surgically induced peritonitis by the cecal ligation and puncture procedure. Senescent mice died in a significantly shorter time following surgery than mature mice (median time to death, 24.4 versus 38.5 h, respectively; P less than or equal to 0.001). Blood, liver, spleen and occasionally, ceca were obtained at 2 and 12 h after the cecal ligation and puncture procedure and immediately following death, to characterize the bacterial kinetics of the model. Qualitative and quantitative aerobic, anaerobic, and coliform cultures were performed. No age-related differences were found in the types of bacteria isolated throughout the time course of progressive sepsis. In mice in the mature and senescent age groups, at 2 and 12 h postsurgery, gram-negative anaerobes and gram-positive aerobes predominated in all tissues that were cultured. At the time of death, however, blood and tissue isolates consisted predominantly of coliform bacteria. The shift from mixed infection during sepsis to predominantly gram-negative bacterial infection reflected a similar progressive shift in bacterial types found in the cecum. At death, senescent mice had 100-fold fewer coliform bacteria in the bloodstream than those found in mature mice (2.5 x 10(9) versus 4.6 x 10(11), respectively). The increased sensitivity of aged mice to invasive bacterial infection documented in this series of experiments accords well with human epidemiologic experience and demonstrates the appropriateness of the model for continued investigations of sepsis in the aged.

Increased basal gluconeogenesis in the aged rat

Post-absorptive gluconeogenesis from lactate measured in vivo increases 3-fold in 24-month-old rats compared to 3-month-old animals. Fractional lactate turnover rates showed no significant differences between the two groups of animals. Lower plasma glucose concentrations and insulin-glucagon ratios may explain the increase in gluconeogenesis observed in aged rats.