glutaminase and Starvation

The distribution of glutaminase expression in a uricotelic species, the chicken, has been examined using cDNA probes to the rat isozymes. The results suggest that chickens do not possess a glutaminase isozyme equivalent to the liver-type isozyme of mammalian liver. Measurements of enzymic activity also showed very low glutaminase activity in chicken liver. Extra-hepatic tissues in the chicken do express a glutaminase isozyme mRNA which is detected by rat kidney-type glutaminase cDNA. The abundance of this mRNA was highest in kidney and breast muscle and relatively abundant in brain, spleen and adipose tissue. Chicken small intestine expressed relatively low levels of the mRNA. The high level of glutaminase mRNA in chicken pectoralis muscle was accompanied by high glutaminase enzymic activity. In contrast, in mixed leg muscle glutaminase mRNA was barely detectable by Northern blot and glutaminase activity was relatively low. Starvation for 48 h resulted in a slight decrease in the activity of glutaminase in pectoralis muscle, but a large decrease in the relative abundance of the mRNA. The results suggest that in the chicken, hepatic glutamine hydrolysis is not quantitatively important, but skeletal muscle may be a major site of glutamine catabolism.

Topics: Animals; Chickens; Enzyme Activation; Gene Expression; Glutaminase; Isoenzymes; Kidney; Liver; Male; Pectoralis Muscles; Phosphates; Rats; RNA, Messenger; Species Specificity; Starvation; Tissue Distribution

Previous studies have documented an increase in hepatic plasma membrane glutamine transport in the tumor-bearing rat, but the effects of tumor burden on hepatic glutaminase expression have not been carefully studied. The purpose of this study was to examine the effects of tumor burden and food intake on hepatic glutaminase expression. Rats were implanted with syngeneic methylcholanthrene-induced fibrosarcoma tumor tissue; control rats were sham operated and pair-fed every 24 hr. Northern blotting was used to assay the effect of tumor burden and fasting on hepatic glutaminase mRNA levels, using beta-actin mRNA as a control. Hepatic glutaminase mRNA levels in livers of pair-fed controls were found to be 4-fold greater than levels in livers of tumor-bearing animals. Examination of food intake patterns in these animals indicated that pair-fed controls ate their allotted chow quickly while tumor-bearing rats ate small amounts throughout each 24 hr period. This observation suggested that the differences in glutaminase mRNA levels may be due to a period of fasting by pair-fed animals which was not experienced by the tumor-bearing group. Hepatic glutaminase mRNA levels rapidly increased in normal rats during acute fasting to levels 5.5-fold greater than fed animals. Glucose feeding and insulin injection rapidly reversed the effect of fasting on hepatic glutaminase mRNA levels in normal rats. Tumor-bearing rats also exhibited upregulation of hepatic glutaminase mRNA levels in response to fasting.. (1) Tumor burden itself does not alter hepatic glutaminase expression, at least at the pre-translational level. Instead, differences in hepatic glutaminase mRNA content are due to differences in food intake patterns. (2) Hepatic glutaminase mRNA levels are rapidly upregulated in response to fasting, an effect which appears to be linked to a decrease in plasma insulin concentrations. Because tumor-bearing rats eat regularly over a 24 hr period (albeit in small increments), thereby maintaining the plasma insulin concentration, hepatic glutaminase mRNA may not rise as it does in pair-fed controls whose daily chow intake is complete within hours of food allocation. (3) This study indicates that differences in the timing of food intake between tumor-bearing rats and pair-fed controls can alter the expression of genes that are influenced by nutrient availability. These differences should be taken into account when designing studies which involve pair-feeding to control nutrient intake.

Topics: Acute Disease; Animals; Fibrosarcoma; Gene Expression; Glucose; Glutaminase; Insulin; Liver; Male; Methylcholanthrene; Neoplasm Transplantation; Rats; Rats, Inbred F344; Starvation

Mammalian liver possesses a unique isozyme of phosphate-activated glutaminase that is subject to long-term regulation. In rats during starvation or after consumption of diets containing high amounts of protein (60%), hepatic glutaminase activity was 100% higher than in rats fed a 20% protein diet. Conversely, rats fed low protein diets (0 and 5%) had lower hepatic glutaminase activity when compared with rats fed the 20% protein diet. Differences in activity with different dietary protein levels were not due to differences in the amount of food consumed. The relative abundance of mRNA encoding hepatic glutaminase was lower in rats fed 0% protein and higher in those starved or fed 60% protein diet when compared with rats fed the 20% protein diet. The mRNA elongation assay in hepatic nuclei isolated from these animals demonstrated that the rate of transcription of the glutaminase gene was also different in rats starved or fed different levels of dietary protein. Overall, the results indicate that differences in hepatic glutaminase activity in rats starved or fed different levels of protein are mainly due to differences in the rate of transcription of the gene. In this way the regulation of hepatic glutaminase expression is similar to that seen for other enzymes involved in hepatic amino acid catabolism but differs markedly from that of renal glutaminase, in which changes in transcription rate are not observed and alterations of mRNA turnover are the principle mechanism of long-term regulation.

Topics: Animals; Cell Nucleus; Dietary Proteins; Gene Expression Regulation; Glutaminase; Liver; Male; Rats; Rats, Sprague-Dawley; RNA, Messenger; Starvation; Transcription, Genetic

Phosphate-activated glutaminase (PAG) was assayed in homogenates of brain cerebellum, hippocampus or striatum from normal, starved for 48 h to 120 h or streptozotocin-diabetic rats. Only the hippocampal enzyme was increased (47%) by diabetes. Starvation had no effect in any of the regions studied. PAG of synaptosomes or of non-synaptosomal mitochondria from the hippocampus was also increased by 48% and 22% respectively in diabetes. PAG of synaptosomes from the cortex, the cerebellum, or the striatum or of the non-synaptosomal mitochondria from the cortex were not affected by diabetes or prolonged (120 h) starvation. A suggestion is presented that peripheral insulin, indirectly, may regulate PAG activity in a specific region of the rat brain.

Topics: Animals; Brain; Cerebellum; Corpus Striatum; Diabetes Mellitus, Experimental; Enzyme Activation; Glutaminase; Hippocampus; Male; Mitochondria; Phosphates; Rats; Rats, Inbred Strains; Starvation; Synaptosomes

Starvation decreases activities of some glycolytic and citric acid-cycle enzymes, and increases those of glucose 6-phosphatase and fructose bisphosphatase, whereas that of glutaminase is unchanged. These findings may be of significance for the control of glucose metabolism in the absorptive cells of the intestine.

Topics: Animals; Citric Acid Cycle; Glutaminase; Glycolysis; In Vitro Techniques; Intestinal Mucosa; Intestine, Small; Male; Rats; Rats, Inbred Strains; Starvation

Kidneys of rats fed for 10 days a diet containing protein from Cajanus cajan were found to show an increase in the maleate-induced phosphate-independent glutaminase (PIG) activity as compared to the rats fed a diet containing egg protein. These changes could be reversed by reversing the diets. PIG is known to possess the catalytic function of gamma-glutamyl transpeptidase, which showed parallel changes. Starvation of adult rats for 24 h as well as the growth of young rats into adults resulted in an increase in the two enzyme activities. The alteration of the enzyme activities is in agreement with the postulated physiological role of these two enzymes.

Topics: Animals; Dietary Proteins; Egg Proteins; Fabaceae; gamma-Glutamyltransferase; Glutaminase; Growth; Kidney; Male; Plant Proteins, Dietary; Plants, Medicinal; Rats; Starvation

1. Slices of duodenum and jejunum produce ammonia from glutamine in vitro. 2. Ammoniagenesis does not increase in response to acidosis or potassium deficiency, two conditions known to cause enhanced ammoniagenesis in the kidney. 3. Gut contains glutaminase 1 as well as gamma-glutamyl transpeptidase. 4. These enzymes do not show any increase during starvation.

Topics: Acidosis; Acute Disease; Ammonia; Animals; Chronic Disease; Duodenum; gamma-Glutamyltransferase; Glutaminase; Glutamine; In Vitro Techniques; Intestine, Small; Jejunum; Organ Specificity; Rats; Starvation

The effects of starvation on the acid-base status of the rat and on the glucoeogenic and ammoniagenic capacity of rat renal-cortical slices were examined. Starvation for 48 or 72 hr did not affect acid-base status, and urinary ammonia production did not change. Kidney cortical slices from starved as compared to fed rats showed increased gluconeogenic capacity when incubated with the substrated pyruvate, succinate, fumarate, malate, 2-oxyoglutarate, glutamine and glutamate. Renal cortical tissue from starved rats also had increased activity of the gluconeogenic enzyme phosphoenolpyruvate carboxykinase. Renal cortical slices from starved rats did not differ from those from fed rats in the ability to produce ammonia from glutamine or glutamate, nor was there any difference inhe activity of glutaminase between these groups. These results show that renal gluconeogenic capacity is increased in starved rats in the absence of systemic acidosis, and starvation does not lead to an increase in urinary ammonia excretion or renal ammoniagenic capacity.

Topics: Acid-Base Equilibrium; Ammonia; Animals; Blood; Dicarboxylic Acids; Gluconeogenesis; Glutaminase; Hydrogen-Ion Concentration; Kidney; Kidney Cortex; Phosphoenolpyruvate Carboxykinase (GTP); Rats; Starvation

Topics: Aging; Animals; Animals, Newborn; Asparaginase; Cell Biology; Cytoplasm; Embryo, Mammalian; Feeding Behavior; Female; Glutaminase; Hydrocortisone; Kidney; Liver; Milk; Neoplasm Transplantation; Pregnancy; Rats; Sex Factors; Starvation; Weaning