Vasopressin and nitric oxide synthesis after three days of water or food deprivation

Nitric oxide metabolites in hypoxia, freezing, and hibernation of the wood frog, Rana sylvatica

Nitric oxide (NO) is a gaseous free radical that in diverse organisms performs many signaling and protective functions, such as vasoregulation, inhibition of apoptosis, antioxidation, and metabolic suppression. Increased availability of NO may be especially important during life-history periods when organisms contend with multiple stresses. We investigated dynamics of the NO metabolites, nitrite (NO₂^-) and nitrate (NO₃^-), in the blood plasma, heart, liver, and skeletal muscle of the wood frog (Rana sylvatica), an amphibian that endures chronic cold, freezing, hypoxia, dehydration, and extended aphagia during hibernation. We found elevated concentrations of NO₂^- and/or NO₃^- in the plasma (up to 4.1-fold), heart (3.1-fold), and liver (up to 4.1-fold) of frogs subjected to experimental hypoxia (24 h, 4 °C), and in the liver (up to 3.8-fold) of experimentally frozen frogs (48 h, - 2.5 °C), suggesting that increased NO availability aids in survival of these stresses. During a 38-week period of simulated hibernation, NO₂^- and/or NO₃^- increased in the plasma (up to 10.4-fold), heart (up to 3.3-fold), and liver (5.0-fold) during an initial 5-week winter-acclimatization regimen and generally remained elevated thereafter. In hibernation, plasma NO₂^- was higher in frogs indigenous to Interior Alaska than in conspecifics from a temperate locale (southern Ohio), suggesting that NO availability is matched to the severity of environmental conditions prevailing in winter. The comparatively high NO availability in R. sylvatica, a stress-tolerant species, together with published values for other species, suggest that the NO protection system is of general importance in the stress adaptation of vertebrates.

Effects of physical training on the immune system in diabetic rats

AIMS

This study aims to investigate the influence of physical training on the immune system of diabetic rats.

MATERIALS AND METHODS

Adult male Wistar rats were distributed into Sedentary Control (SC), Trained Control (TC), Sedentary Diabetic (SD) and Trained Diabetic (TD) groups were used. Diabetes was induced by alloxan (32 mg/bw-i.v.). Training protocol consisted of swimming, at 32 +/- 1 degrees C, one hour/day, five days/week, supporting an overload equivalent to 5% of the body weight, during four weeks. At the end of the experiment the rats were sacrificed by decapitation and blood samples were collected for glucose, insulin, albumin, hematocrit determinations, total and differential leukocyte counting. Additionally, liver samples for glycogen analyses were obtained.

RESULTS

The results were analyzed by one way at a significance level of 5%. Diabetes reduced blood insulin, liver glycogen stores and increased blood glucose and neutrophil count. Physical training restored glycemia, liver glycogen levels, neutrophils and lymphocytes count in diabetic rats.

CONCLUSIONS

In summary, physical training was able to improve metabolic and immunological aspects in the experimental diabetic rats.

Long-term physical training increases liver IGF-I in diabetic rats

Diabetes reduces the serum levels of insulin-like growth factor-I (IGF-I) and physical training may prevent this reduction. Almost all circulating IGF-I is produced and secreted by the liver. To examine the influence of moderate physical training on liver IGF-1 levels in diabetes, male Wistar rats were given a single dose of alloxan (30 mg/kg b.w.) to induce diabetes and then randomly allocated to sedentary or trained groups. The training protocol consisted of a 1h swimming session/day, five days/week for eight weeks with a load corresponding to 5% of the body weight. These two groups were compared with sedentary or trained non-diabetic rats (controls). A subcutaneous insulin tolerance test (ITT) was performed at the 6th week of experiment. At the end of the training period, the rats in all groups were sacrificed and blood was collected for the quantification of hematocrit and serum glucose, insulin, triglycerides, albumin, GH and IGF-1. Skeletal muscle and hepatic glycogen levels and hepatic triglyceride, protein, DNA and IGF-I concentrations were also determined. Diabetes reduced the serum insulin, GH and IGF-I concentrations, and the hepatic protein/DNA ratio and IGF-I concentrations, but increased serum glucose and triglyceride levels. Serum glucose removal during ITT was increased in the trained diabetic animals compared to sedentary control. Physical training reduced the serum glucose and triglyceride levels but increased the muscle glycogen content and restored the hepatic protein/DNA ratio and serum and hepatic IGF-I in diabetic rats. In conclusion, long-term chronic exercise improved the metabolic state and attenuated the reduction in serum and hepatic IGF-I concentrations caused by diabetes.

Fuel economy in food‐deprived skeletal muscle: signaling pathways and regulatory mechanisms

Energy deprivation poses a tremendous challenge to skeletal muscle. Glucose (ATP) depletion causes muscle fibers to undergo rapid adaptive changes toward the use of fatty acids (instead of glucose) as fuel. Physiological situations involving energy deprivation in skeletal muscle include exercise and fasting. A vast body of evidence is available on the signaling pathways that lead to structural/metabolic changes in muscle during exercise and endurance training. In contrast, only recently has a systematic, overall picture been obtained of the signaling processes (and their kinetics and sequential order) that lead to adaptations of the muscle to the fasting state. It has become clear that the reaction of the organism to food restraint or deprivation involves a rapid signaling process causing skeletal muscles, which generally use glucose as their predominant fuel, to switch to the use of fat as fuel. Efficient sensing of glucose depletion in skeletal muscle guarantees maintained activity in those tissues that rely entirely on glucose (such as the brain). To metabolize fatty acids, skeletal muscle needs to activate complex transcription, translation, and phosphorylation pathways. Only recently has it become clear that these pathways are interrelated and tightly regulated in a rapid, transient manner. Food deprivation may trigger these responses with a timing/intensity that differs among animal species and that may depend on their individual ability to induce structural/metabolic changes that serve to safeguard whole-body energy homeostasis in the longer term. The increased cellular AMP/ATP ratio induced by food deprivation, which results in activation of AMP-activated protein kinase (AMPK), initiates a rapid signaling process, resulting in the recruitment of factors mediating the structural/metabolic shift in skeletal muscle toward this change in fuel usage. These factors include peroxisome proliferator-activated receptor (PPAR)gamma coactivator-1alpha (PGC-1alpha), PPARdelta, and their target genes, which are involved in the formation of oxidative muscle fibers, mitochondrial biogenesis, oxidative phosphorylation, and fatty acid oxidation. Fatty acids, besides being the fuel for mitochondrial oxidation, have been identified as important signaling molecules regulating the transcription and/or activity of the genes or gene products involved in fatty acid metabolism during food deprivation. It is thus becoming increasingly clear that fatty acids determine the economy of their own usage. We discuss the order of events from the onset of food deprivation and their importance.

Angiotensin converting enzyme activity and nitric oxide level in serum patients with dehydration

Angiotensin converting enzyme (ACE) and nitric oxide (NO) have been suggested to be involved in the regulation of fluid homeostasis. In the present investigation, ACE activity and NO levels were determined in serum of 20 patients (10 men and 10 women) with dehydration caused by gastroenterocolitis and 20 healthy individuals (10 men and 10 women). Serum and tissue ACE activity was determined by spectrophotometric method using hippuryl-l-histidyl-l-leucine (Hip-His-Leu) as a substrate. NO synthesis was determined by measuring the products of NO, nitrite and nitrate. The concentration of nitrites was determined by classic colorimetric method using Griess reagent. Nitrate concentration was determined indirectly by their reduction with elementary zinc into nitrite. Results have shown that serum ACE activity in patients with dehydration (36,46+/-2,74 U/L) is statistically higher then in healthy individuals (28,71+/-1,77 U/L, p<0,05). The average level of nitrites/nitrates in serum of patients with dehydration (30,57+/-1,05 microM; mean +/- SEM) is also statistically higher then in healthy individuals (12,44+/-0,60 microM, p<0,0001). There was no correlation between ACE activity and NO production. The results indicate that ACE and NO may participate in the regulation of the alteration in blood flow and in the regulation of the water balance in patients with dehydration.