Paloma Hortelano

The n-3 polyunsaturated fatty acid levels in rat tissue lipids increase in response to dietary olive oil relative to sunflower oil.

In the present study, changes in phospholipid compositions of liver microsomes, erythrocyte membranes, platelets, aorta, cardiac muscle and brain of rats fed olive oil were compared with those of rats fed sunflower oil. Four groups of rats starting at weaning were fed for four weeks a basal diet containing 5 or 25% olive oil or sunflower oil. We found that oleic acid was higher and linoleic acid was lower in membrane phospholipids of olive oil fed rats compared to sunflower oil fed rats. Polyunsaturated fatty acids of the n−3 series were markedly elevated in all tissues of rats on the olive oil diets relative to those on the sunflower oil diets. The results are consistent with a lower linoleic/linolenic acid ratio induced by the olive oil diets, suggesting a positive correlation between olive oil ingestion and n−3 polyunsaturated fatty acid levels in cell and tissue lipids. The study suggests that an adequate intake of olive oil may enhance the conversion of n−3 fatty acids.

Effect of dietary olive and sunflower oils on the lipid composition of the aorta and platelets and on blood eicosanoids in rats.

The effects on aortic and platelet fatty acid compositions and on blood levels of prostacyclin and thromboxane A2 of low- and high-fat diets containing olive oil or sunflower oil were studied. For 4 weeks, four groups of weanling rats were fed a basal diet containing 5% or 25% olive oil or sunflower oil. Rats fed olive oil diets showed higher levels of 18:1(n-9) and polyunsaturated fatty acids of the n-3 series and lower percentages of 18:0 and 18:2(n-6) in aortic and platelet phosphatidylcholine and phosphatidylethanolamine than those fed the sunflower oil diets. Arachidonic acid increased in platelet phosphatidylethanolamine and aortic phosphatidylcholine of rats fed the diet containing 5% sunflower oil compared with those fed 5% olive oil. Plasma 6-ketoprostaglandin F1 alpha increased in both groups of animals fed olive oil while these rats also showed the lowest levels of serum thromboxane B2 and plasma cholesterol. Olive oil feeding leads to changes in lipid metabolism of the vascular compartment that could be favorable in the prevention of thrombosis and atherosclerosis.

Modulation of hepatic and intestinal glutathione S-transferases and other antioxidant enzymes by dietary lipids in streptozotocin diabetic rats.

Antioxidant enzymes in liver and small intestine were investigated using control and streptozotocin diabetic rats fed diets with 5% olive, sunflower or fish oil for five weeks. In liver, Glutathione Peroxidase and Superoxide Dismutase decreased and in intestine Glutathione-S-transferase (GST) increased by diabetes. In isolated jejunum and ileum, this increase in GST activity was due to an increase in GST-alpha and -mu isoenzymes in jejunum and GST-alpha, mu and -pi in ileum. Since GST plays an important role in protecting tissues from oxidative damage, our results highlight the role of the intestine against free radicals in physiological or pathological situations.

The mechanism of the increase in renal ammoniagenesis in the rat with acute metabolic acidosis

Chronic metabolic acidosis causes several biochemical changes in the rat kidney: perhaps the most prominent of these is the increase in ammonia production from glutamine and the increase in activity of phosphate-dependent glutaminase [ 11. The changes with acute acidosis are less clear and although there is an early increase in total renal production of ammonia [2] no enzymatic change has been described to explain this. Since changes in pH and bicarbonate alone could not be the stimulus for this renal metabolic adaptation, we looked for and demonstrated the presence of a factor in the plasma of acutely acidotic rats which stimulated glutamine uptake and ammoniagenesis by renal slices from normal rats [3]. We now describe a possible mechanism for this ammoniagenie response to acute acidosis in the rat. Our studies have focussed on the kidney since although the liver, brain and intestine metabolise glutamine, none of these organs show any enzymatic adaptation in response to metabolic acidosis.

Increased Diaphragm Expression of GLUT4 in Control and Streptozotocin-Diabetic Rats by Fish Oil-Supplemented Diets

Dietary fat intake influences plasma glucose concentration through modifying glucose uptake and utilization by adipose and skeletal muscle tissues. In this paper, we studied the effects of a low-fat diet on diaphragm GLUT4 expression and fatty acid composition in control and streptozotocin-induced diabetic rats. Control as well as diabetic rats were divided into three different dietary groups each. Either 5% olive oil, 5% sunflower oil, or 5% fish oil was the only fat supplied by the diet. Feeding these low-fat diets for 5 wk induced major changes in fatty acid composition, both in control and in diabetic rats. Arachidonic acid was higher in diabetic olive and sunflower oil-fed rats with respect to fish oil-fed, opposite to docosahexaenoic acid which was higher in diabetic fish oil-fed rats with respect to the other two groups. Animals receiving a fish oil diet had the lowest plasma glucose concentration. GLUT4 expression in diaphragm, as indicated by GLUT4 protein and mRNA, is modulated both by diabetes and by diet fatty acid composition. Diabetes induced a decrease in expression in all dietary groups. Plasma glucose levels correlated well with the increased amount of GLUT4 protein and mRNA found in fish oil-fed groups. Results are discussed in terms of the influence that arachidonic and n−3 polyunsaturated fatty acids may exert on the transcriptional and translational control of the GLUT4 gene.

Metabolic behaviour in isolated populations of proximal and distal rat renal tubules

Abstract A modified and improved enzyme digestion and density gradient separation procedure to obtain enriched suspension of proximal and distal renal tubules with high yield and viability has been described. Separation was achieved by suspending the tissue in 40% isosmotic Percoll. The fourth band, formed by a 47.3% of the recovered tubules, was an almost pure preparation of proximal renal tubules (> 95%). More than 80% of enriched distal segments were isolated in the second band, formed by a 26.8% of the recovered tubules. The proximal tubular preparation was shown to be gluconeogenic and ammoniagenic (about 75% of the total activity) whereas the distal tubular suspension was found to be glycolytic (almost 80%). Analysis of the enzyme activities confirms the heterogeneous metabolic behaviour of these segments of the nephron.

Metabolic adaptation of renal carbohydrate metabolism. V.In vivo response of rat renal-tubule gluconeogenesis to different diuretics

We have studied the effects of the diuretics mersalyl, furosemide and ethacrynic acid on renal gluconeogenesis in isolated rat-kidney tubules and on the activities of the most important gluconeogenic and glycolytic enzymes in both fed and fasted rats. Mersalyl (15 mg.kg−1 animal weight) significantly decreased the rate of gluconeogenesis in well-fed rats (68%) as well as in 24 and 48-h fasted ones (33 and 37% respectively). This inhibition occurred when lactate, pyruvate, glycerol or fructose were used as substrates. Ethacrynic acid at a dose of 50 mg.kg−1 animal weight provoked a transient inhibition of renal glucose production by almost 20% but only in fed rats with lactate as substrate, whereas the same dose of furosemide did not affect this metabolic pathway.Parallel to these changes, mersalyl caused a significant inhibition in the maximum activity of the most important gluconeogenic enzymes, phosphoenolpyruvate carboxykinase, fructose 1,6-bisphosphatase and glucose 6-phosphatase, in both fed and fasted rats. Neither ethacrynic acid nor furosemide produced any variations in the activities of these enzymes. The activity of the glycolytic enzymes phosphofructokinase and pyruvate kinase was not modified by these diuretics. Nevertheless, the activity of the thiol-enzyme glyceraldehyde 3-phosphate dehydrogenase was severely inhibited by mersalyl and to a lesser extent by the other diuretics. This inhibition was higher in fasted than fed rats. Hence, we conclude that the inhibitory effect of mersalyl on renal gluconeogenesis is due, at least partly, to a decrease in the flux through the gluconeogenic enzymes. Blood glucose was not modified after diuretic treatment in fed animals whereas mersalyl decreased the levels of blood glucose in 24-h fasted rats. Thein vivo effects of diuretics on gluconeogenesis correlate well with the previously observedin vitro effects, although ethacrynic acid was less potent as an inhibitorin vivo, probably because of its rapid clearance.

Role of α-adrenergic stimuli in the control of rat renal ammoniagenesis

The effects of phenylephrine on renal ammoniagenesis and the involvement of Ca2+ in phenylephrine action were investigated in isolated proximal fragments of rat-kidney tubules. Phenylephrine stimulated renal ammoniagenesis from 1 and 2 mM glutamine whereas no significant changes took place at a higher concentration of glutamine (20 mM). Stimulation of ammonia synthesis by phenylephrine was found to be linear with time and dose-dependent between 10−9 and 10−4 M. Phenylephrine-stimulated ammoniagenesis was blocked by phentolamine (10 μM) but not by propranolol (10 μM) confirming that the effect is mediated by α-adrenergic stimuli. No stimulatory effect of phenylephrine was observed in Ca2+ depleted proximal tubule fragments, suggesting that Ca2+ is required in this adrenergic response.

Renal gluconeogenic response to different diuretics. I: In vitro effects of mersalyl, furosemide and ethacrynic acid on isolated rat renal tubules

Abstract The effect of in vitro addition of three different diuretics: mersalyl, furosemide and ethacrynic acid on glucose production by isolated kidney tubules from fed and 24 hours starved rats has been studied. All three diuretics induce effects which are dose and time dependent. Mersalyl and ethacrynic acid inhibit the rate of renal gluconeogenesis using lactate as substrate. In tubules obtained from fed animals ethacrynic acid exert more pronounced effects than mersalyl although the K 1 (the concentration required to reach half of the maximun inhibition) for both diuretics was 10 -4 M. Similar results are obtained when using 24 hours fasted animals although the effect of the diuretics is seen from 10 -4 M. Furosemide addition causes differential effects with respect to the previously mentioned diuretics. When using tubules from fed rats the rate of gluconeogenesis is not significantly changed whereas on tubules from 24 hours starved rats this diuretic stimulates gluconeogenesis in a dose dependent manner reaching almost 140% of control values. Different sites of action of the diuretics on the enzymes of the glycolytic-gluconeogenic pathway are discussed, either exerted directly or indirectly by changing intracellular concentrations of different ions.

Involvement of glucocorticoids in the stimulation of rat kidney phosphoenolpyruvate carboxykinase activity after liver intoxication by carbon tetrachloride

The enhancement of rat kidney cortex phosphoenolpyruvate carboxykinase activity during acute liver intoxication by carbon tetrachloride (CCl4) did not appear to be related to metabolic acidosis. Blood glucocorticoids were higher in CCl4-treated animals than in controls. Adrenalectomy fully counteracted the stimulation of renal phosphoenolpyruvate carboxykinase activity and gluconeogenic capacity brought about by CCl4 administration. It is concluded that glucocorticoids are involved in the renal response to acute liver intoxication by CCl4.