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R Curi

Publications and source records attributed to R Curi.

At least 181 records · Page 10Linked to original sources
PubMed1991

Hexose metabolism in pancreatic islets: pyruvate carboxylase activity.

The anaplerotic hypothesis for insulin release postulates that an increased generation of malonyl-CoA, acyl residues and diacylglycerol in nutrient-stimulated pancreatic islets may couple the catabolism of nutrient secretagogues to more distal events in the secretory sequence. In the light of this hypothesis, pyruvate carboxylase activity was measured in rat pancreatic islets using two distinct radioisotopic procedures. The first procedure is based on the conversion of oxalacetate generated from pyruvate to 14C-labelled citrate in the presence of [1-14C]acetyl-CoA and citrate synthase. The second technique involves the conversion of 14C-labelled oxalacetate generated from [1-14C]pyruvate to radioactive aspartate in the presence of L-glutamate and glutamate-oxalacetate transaminase. Pyruvate carboxylase activity amounted to 10 pmol/min per islet, was restricted to mitochondria, displayed a Km for pyruvate close to 0.4 mM, and demonstrated dependency towards ATP (apparent Ka close to 0.1 mM), Mg2+ and acetyl-CoA. It is proposed that pyruvate carboxylase activity accounts for the generation of 14C-labelled amino acids other than alanine in islets exposed to D-[3,4-14C]glucose and participates to the pyruvate/citrate shuttle for the transport of acetyl-CoA out of the mitochondria in nutrient-stimulated islets.

Acetyl Coenzyme A↗
PubMed1991

Hormonal control of macrophage function and glutamine metabolism.

Murine macrophages have been reported to utilize glutamine at high rates. However, the role of glutamine in macrophage function is still unknown. In the present study, the maximum glutaminase activity of macrophages was investigated under several endocrine dysfunctions that are known to cause alterations in macrophage function. The results obtained suggest that glutamine might play an important role in the onset of phagocytosis in inflammatory macrophages. Moreover, the studies show that insulin, glucocorticoids, and thyroid hormones may be responsible for the regulation of glutamine metabolism and, consequently, of macrophage function.

Adrenalectomy↗
PubMed1991

Metabolic changes induced by w-3 polyunsaturated fatty acid rich-diet (w-3 PUFA) on the thymus, spleen and mesenteric lymph nodes of adult rats.

The maximal activity of key enzymes of glycolysis, pentose phosphate pathway, TCA cycle and glutaminolysis were measured in the immune tissues of rats fed w-3 PUFA during 6 weeks. Total lipid peroxidation and glutathione peroxidase activity were also measured. The hexokinase activity was enhanced 4-fold in the spleen and thymus, doubled in the liver and was diminished in mesenteric lymph nodes (35%). Citrate synthase activity was decreased in the spleen and lymph nodes and increased in the thymus. G-6-PDH activity was increased 2-fold in the spleen and mesenteric lymph nodes and by 20% in the thymus whereas it was reduced (66%) in the liver. Glutathione peroxidase activity and total lipid peroxides increased in all tissues of rats fed w-3 PUFA. The results presented here suggest that w-3 PUFA, by causing important metabolic changes in the immune tissues and lipid peroxidation may lead to changes of immune function.

Animals↗
PubMed1991

Effect of the i.v. administration of non-activated lymphocytes on rat plasma insulin and glucose levels.

Although several studies have shown the effect of cytokines on islet B cell function, the role of circulating cells in the control of insulin secretion has not been investigated. The effect of lymphocyte administration on plasma glucose and insulin levels was examined in male Wistar albino rats weighing 180-200 g. The animals were anesthetized and the jugular vein was cannulated for saline or lymphocyte injection (10(6) cells in 1 ml) and blood collection after 5, 10, 15, 20, 30, 45 and 60 min. A marked increase in plasma insulin levels (180 microU/ml as compared to 56 microU/ml in the control group, at 20 min) and an unexpected increase (P < 0.05) in blood glucose levels (at 60 min only) were observed after lymphocyte administration. Similar experiments undertaken with simultaneous administration of inhibitors of arachidonic acid metabolism, indomethacin and nordihydroguairetic acid at 1 mg/kg body weight, suggest that this effect of lymphocytes is not mediated by prostaglandins or leukotrienes.

Animals↗
PubMed1991

Effect of polyunsaturated (PUFA n-6) and saturated fatty acids-rich diets on macrophage metabolism and function.

Previous reports of our laboratory have shown that PUFA (n-6)-rich diets cause important changes of the metabolism of the immune tissues. In this study, alterations of macrophage metabolism and function were examined in rats fed polyunsaturated (UC) or saturated (SC) fatty acids-rich diets during 6 weeks. The UC group decreased intraperitoneal cell migration and macrophage phagocytosis. These changes were related to modifications of macrophage metabolism. The UC group showed also increased G-6-PDh in inflammatory macrophages. These findings suggest that pentose-phosphate pathway is not the unique metabolic factor to control phagocytosis. PUFA-rich diet reduced glutaminase activity. Therefore, this amino acid might be one of the possible metabolic reasons for the impaired macrophage function observed.

Animals↗
PubMed1990

Meal-feeding and physical effort. 1. Metabolic changes induced by exercise training.

To evaluate the consequences of the combination of meal-feeding (which causes in the long term several adaptations that lead to saving stored energetic substrates), rats subjected to a 2-hr feeding/22-hr fasting schedule were forced to swim 30 min everyday at a fixed hour during four weeks. The results indicate that meal-fed exercised rats: 1) increase food intake above that found in the nonexercising and the corresponding (nonfood-restricted) controls; 2) did not lose weight (in contrast to the controls); 3) initially had a high glycogen mobilization but at the end of the fourth week started to save hepatic glycogen again, despite the intense energy demanding exercise; 4) maintained a slight hyperglycemia; 5) mobilized less free fatty acids than the nonexercising meal-fed rats, probably due to higher insulinemia; 6) had a lower content of ascorbic acid in the adrenal glands in comparison to the control exercising rats; this suggests that the exercise was less stressful in the latter group.

Animals↗
PubMed1990

Meal-feeding and physical effort. 2. Metabolic changes induced by an acute exercise.

In this study, rats under meal-feeding up to four weeks were submitted to a sudden exercise (swimming) to evaluate the effects of a behavior that requires mobilization of a large amount of energy on some physiological parameters already changed due to the chronic food-restriction. During exercise meal-fed rats: 1) increase the rate of gastric emptying; 2) maintain glycemia more steadily than the controls even during a long-lasting exercise; 3) maintain high liver glycogen concentration and its mobilization starts later on; 4) free fatty acid mobilization is lower than in the controls but during exercise do use much more; 5) keep more glycogen in the muscles (including the heart) than the controls but during the exercise do utilize much more; 6) are slightly less stressful (mainly after a longer exercise) than the controls as suggested by the adrenal ascorbic acid content.

Animals↗
PubMed1990

Insulin secretion in Walker 256 tumor cachexia.

The effect of cachexia on insulin secretion was examined in adult male rats. Isolated islets of Langerhans from Walker 256 tumor-bearing rats secreted less insulin by glucose stimuli as compared with the control group; this was accompanied by significant change in 45Ca2+ outflow rate. Reduced insulin secretion to glucose stimuli in tumor-bearing rats probably led to low insulinemia (one-third). These findings indicate that reduced insulin secretion is probably an important factor for the development of cachexia in Walker 256 tumor-bearing rats.

Animals↗
PubMed1990

Polyunsaturated and saturated fatty acids-rich diets and immune tissues. 1. Fresh weight, DNA content, percentage of lipids and rate of lipogenesis from 3H2O in thymus, spleen and mesenteric lymph nodes.

It has been widely reported that polyunsaturated fatty acids-rich diets (PUFA n-6) cause immunodeficiency. In this study, fresh weight, DNA and lipid content and rate of lipogenesis from 3H2O of thymus, spleen, mesenteric lymph nodes and liver were assessed in rats fed polyunsaturated (UC) or saturated (SC) fatty acids-rich chows. The results obtained indicate that both types of fatty acids caused similar increment of lipid content in the immune tissues. The rate of lipogenesis was decreased only in the thymus of (UC) rats and liver of both experimental groups as compared to control rats. The results of fresh weight and DNA content was decreased only by (UC) diet.

Animals↗
PubMed1990

Polyunsaturated and saturated fatty acids-rich diets and immune tissues. 2. Maximal activities of key enzymes of glutaminolysis, glycolysis, pentose-phosphate-pathway and Krebs cycle in thymus, spleen and mesenteric lymph nodes.

It has been widely reported that polyunsaturated fatty acids (PU-FA n-6) in the diet lead to immunosuppression. In the present study, the activity of key enzymes several metabolic pathways were measured in the immune tissues of rats fed polyunsaturated (UC) or saturated fatty (SC) acids-rich diets. The following enzyme activities were measured: hexokinase, citrate synthase, glucose-6-phosphate dehydrogenase, glutaminase and malic enzyme. The metabolism of immune tissues was markedly changed by the fat content of the diet. However, UC diet determined more significant metabolic changes than SC diet.

Animals↗
PubMed1990

Effects of diet and exercise on the in vivo rates of the triglyceride-fatty acid cycle in adipose tissue and muscle of the rat.

The effects of feeding a low-protein diet (5 percent w/w) and daily exercise on the rates of substrate (futile) cycling between triglyceride and fatty acids (TG-FA cycle) were studied in rats in vivo using a radiochemical assay that involves following the incorporation of tritium from 3H-H2O into the fatty acid and glycerol moieties of triglyceride. Sixty-four rats were fed either a purified control diet (COND) consisting of 70 percent carbohydrate, 20 percent protein, 5 percent fat or an experimental low protein (LPD) diet consisting of 80 percent carbohydrate, 5 percent protein and 10 percent fat (w/w) and were either exercised six days weekly or remained sedentary for six weeks. Both LPD and exercise training (EXT) were found to increase significantly the rate of TG-FA substrate cycling above the rates observed in dietary and sedentary control groups. The LPD increased significantly the rate of cycling in interscapular brown adipose (IBAT), while adipose (WAT) and diaphragm muscle. EXT increased the rates of substrate cycling in soleus, heart, and diaphragm muscle and WAT. Rate of cycling in cardiac or skeletal muscle was one-twentieth that found in adipose tissue. There were also sex differences in the rate of substrate cycling. Substrate cycling in soleus and heart muscle of male animals were consistently higher than respective female treatment groups. Sedentary and EXT LPD animals weighed significantly less than but consumed a similar amount of food to the respective COND animals. These data provide the first in vivo evidence that the rate of substrate cycling can be increased by diet or by exercise training. The possible importance of TG-FA and other substrate cycles on efficiency of energy metabolism and etiology of obesity are discussed.

Adipose Tissue↗
PubMed1989

The effect of adenine nucleotides on the rate and fate of glutamine utilization by incubated mitochondria isolated from rat mesenteric lymph nodes.

The rate of glutamine utilization by isolated lymphocyte mitochondria is 21.4 nmol/min per mg protein, of which 72% is converted to glutamate. Addition of ATP, ADP or AMP increased the rate of glutamine utilization by 60%. Evidence is presented that this is due to a stimulation of oxoglutarate dehydrogenase activity by ADP: this may account for the stimulation of glutamine utilization by concanavalin A in lymphocyte.

Adenine Nucleotides↗
PubMed1989

Formation of ketone bodies by resting lymphocytes.

1. Both beta-hydroxy-beta-methylglutaryl-coenzyme A synthase and lyase activities are present in rat mesenteric lymphocytes: all of the synthase and almost all (80%) of the lyase were present in the mitochondrial compartment of the cell. 2. A high rate of acetoacetate formation was observed in mesenteric lymphocytes incubated in vitro for 60 min in the absence of added substrate; addition of pyruvate or glutamine increased the "endogenous" rate of acetoacetate formation by about 30%. 3. The rates of ketone body formation are similar to maximal rates observed for rat liver. 4. It is suggested that the high rate of endogenous acetoacetate production occurs from long chain fatty acids: this suggestion is consistent with the reported high "endogenous" rate of O2 consumption by lymphocytes. 5. Of the pyruvate metabolized via pyruvate dehydrogenase in lymphocytes, ca 50-70% could be accounted for as acetoacetate, acetate, 3-hydroxybutyrate and citrate: the fate of the remainder is not known. 6. There was a high rate of endogenous acetoacetate formation by isolated mitochondria from these cells. 7. The rate was doubled by addition of pyruvate or butyrate; it was trebled by addition of propionate, ADP or carbonyl cyanide trichloro-methoxyphenylhydrazone; but it was decreased by addition of antimycin A or glutamine. 8. It is suggested that the high rates of acetoacetate formation in these cells acts as a dynamic "buffer" system for the acetyl coenzyme A (CoA) concentration: that is, acetyl CoA is always available for fatty acid synthesis, cholesterologenesis, chain extension of fatty acids or acetylation of proteins (e.g. for covalent control of their activity) which will be demanded at different stages of the cell cycle. 9. This is another example of branch-point sensitivity in control in cells with the potential for rapid cell division.

Acetoacetates↗
PubMed1989

Maximal activities of key enzymes of glutaminolysis, glycolysis, Krebs cycle and pentose-phosphate pathway of several tissues in mature and aged rats.

1. The maximum activities of some key enzymes, which provide a quantitative indices of flux through several important pathways have been measured in brain, liver, muscle, white and brown adipose tissue and lymphocytes of mature and aged rats. 2. The results were expressed as mumol/min per g fresh weight and nmol/min per mg protein. 3. On the both basis, as compared to mature rats, hexokinase activity is decreased in brown adipose tissue and increased in soleus muscle. 4. Glucose-6-phosphate dehydrogenase activity is decreased in most tissues and increased in brain. 5. Citrate synthase activity, which provides a qualitative index of the Krebs cycle, is decreased in white adipose tissues and lymphocytes. 6. Glutaminase activity is decreased in brain, white and brown adipose tissues but is increased in lymphocytes.

Adipose Tissue↗
PubMed1989

The effect of controlled feeding conditions on the metabolic characteristics of rats.

To evaluate the effect of feeding conditions on blood glucose, insulin and free fatty acid concentrations, rats were maintained on a 2-hr feeding/22-hr fasting (regular-fasted) schedule for 4 weeks. The animals were then subjected to glucose or insulin loads immediately prior to the usual meal time. Animals fasted for only 22 hr (single-fasted) just before the experiments, and rats having access to food ad lib were similarly loaded and tested. The results demonstrate that the regular fasting regime induces certain metabolic alterations well described in the literature for the single-fasted-period to become more pronounced, specifically, a reduction in insulin secretion and a probably increase in peripheral responsiveness to this hormone. In addition, glucose loading was more effective in lowering plasma free fatty acid concentration in rats restricted to a regular fasting scheme.

Animals↗
PubMed1989

Reversibility of metabolic changes induced by feeding schedule in rats.

This study aimed to investigate the effect of free-feeding on rats kept on meal-feeding schedule for a prolonged period. Thus, rats meal-fed for 4 and 20 weeks were given free access to food for subsequent 5 weeks. The metabolic adaptation of higher hepatic glycogen content, low plasma FFA values and sustained glycemia during 22-hr fast, reported for rats subjected to meal-feeding, completely disappeared after free-eating period. The rate of body weight gain increased as a consequence of the free access to food in both groups but the control values (group with food ad lib all the time) were attained only in rats previously submitted to meal-feeding for the shorter period of time (4 weeks). The findings of this study suggest that the recovery of body weight by meal-fed rats, for the control values, seems to depend on the duration of the meal-feeding schedule and the age when it is imposed.

Adaptation, Physiological↗
PubMed1989

Insulin secretion in the isolated islets of single-, regular-fasted and fed rats.

To investigate the alterations in insulin secretion induced by habituation to single daily meal, adult rats were trained on a regular-fasting scheme (2-hr feeding/22-hr fasting) for 4 weeks. Insulin secretion induced by nutrient secretagogues (D-glucose and L-leucine) and the rates of 45Ca2+ outflow and 14C-glucose oxidation were studied in isolated islets obtained from these animals and in fed and 22-hr single-fasted rats. As expected, in the 22-hr fasted group, insulin secretion was drastically decreased although not abolished while 45Ca2+ outflow and 14C-glucose oxidation rates were only partially reduced. However, the regular-fasted rats did not secrete insulin in response to the nutrient secretagogues; calcium entry was not detected although a partial reduction in 14C-glucose oxidation rate was observed. These results suggest that regular fasting induces alterations in pancreatic B-cell glycolytic pathways leading to impairment of calcium efflux and insulin secretion. Such impairment is more pronounced than that induced by a single 22-hr fast.

Animals↗