Effect of ethanol consumption on adult rat liver mitochondrial populations analyzed by flow cytometry

In the present study, the effects of administering ethanol to adult male rats on the distribution of the low fluorescence population (LFP) and high fluorescence population (HFP), and the rhodamine-123 fluorescence intensity of these groups of mitochondria are analyzed by flow cytometry. Our results show that ethanol administration to adult male rats induces a redistribution of the HFP and LFP mitochondrial populations leading to an increase of the less functional HFP mitochondria. In addition, ethanol induced an increase in the mean intensity of green fluorescence of the HFP that is probably related to an increased number of rhodamine-123 binding sites per mitochondria resulting from mitochondria enlargement.

Postnatal changes in rhodamine-123 stained mitochondrial populations are sensitive to protein synthesis inhibitors but mimicked in vitro by ATP

The incubation of term fetus mitochondria with ATP mimicked in vitro the increase in the respiratory control index and in the percentage of the rhodamine-123-low fluorescence population that occurred in vivo immediately after birth, suggesting that both phenomena are closely associated. The administration of streptomycin inhibited the increase in the percentage of the low fluorescence population that occurred immediately after birth, while the administration of cycloheximide even reversed these changes. These results suggest that the in vivo interconversion between mitochondrial forms depends on both cytosolic and mitochondrial protein synthesis.

Inhibition of neonatal brain fuel utilization by valproate and E-delta 2-valproate is not a consequence of the stimulation of the gamma-aminobutyric acid shunt

Stimulation of the gamma-aminobutyric acid (GABA) shunt by valproate and its major metabolite, E-delta 2-valproate, has been proposed to decrease brain energy metabolism. In order to elucidate this hypothesis, the effect of these drugs on substrate utilization in neonatal rat brain slices was studied. The overall rate of lactate utilization was dose-dependently inhibited by both drugs. Valproate and E-delta 2-valproate inhibited both sterol and fatty acid syntheses from 3-hydroxybutyrate. The rate of glucose utilization was not affected by valproate nor E-delta 2-valproate. The inhibition of the GABA aminotransferase by aminooxyacetate decreased lipogenesis from lactate, 3-hydroxybutyrate and glucose. The inhibitor of the mitochondrial pyruvate carrier, alpha-cyano-4-hydroxycinnamate, strongly decreased the rate of lactate, 3-hydroxybutyrate and glucose utilization, suggesting that the inhibition of pyruvate mitochondrial carrier is not the mode of action of these drugs. It is suggested that inhibition of plasma membrane monocarboxylate carrier by valproate and E-delta 2-valproate, but not the activation of the GABA shunt, is responsible for the inhibition of the brain fuel utilization.

Regulation of lactate metabolism by albumin in rat neurons and astrocytes from primary culture

The possible role played by albumin in regulating brain metabolism during development has been studied. The effects of fatty acid-free BSA on lactate, glucose, 3-hydroxybutyrate, and glutamine oxidation and lipogenesis by rat neurons and astrocytes from primary culture were studied. The rate of lactate oxidation and lipogenesis by neurons and astrocytes in the presence of BSA greatly exceeded that observed for glucose, 3-hydroxybutyrate, or glutamine, suggesting that lactate may be a key substrate for brain development. BSA strongly stimulated the rate of lactate, 3-hydroxybutyrate, and glutamine incorporation into lipids in both neurons (677%, 726%, and 250%, respectively) and astrocytes (415%, 393%, and 215%, respectively), possibly by binding long-chain acyl-CoA excesses, potent inhibitors of acetyl-CoA carboxylase. However, BSA decreased the rate of lipogenesis from glucose in both neurons (34%) and astrocytes (55%), probably by inhibiting glycerol-borne phospholipid synthesis. BSA significantly increased the rates of lactate (61%) and glucose (32%) oxidation by astrocytes but not those of 3-hydroxybutyrate and glutamine, suggesting that BSA may stimulate pyruvate oxidation. However, in neurons BSA did not affect the rate of oxidation of any of the substrates tested, which suggests that pyruvate oxidation is regulated differently in neurons and astrocytes. The results suggest that lactate is the most important substrate for both neurons and astrocytes, stressing the role played by lactate in brain development. Our results also suggest that serum albumin may control brain development by fostering metabolism for growth and differentiation purposes.

Changes in mitochondrial rhodamine-123-fluorescence populations of rat hepatocytes in primary culture

Flow cytometry analysis of mitochondria isolated from rat hepatocytes at different stages of development revealed two different rhodamine-123-stained fluorescence populations distinguishable by their main fluorescence channel. The high-fluorescence population (HFP) was minor, accounting for about 32, 33, and 23% of the total mitochondrial fraction in hepatocytes from preterm, term, and early (1 h) newborn rats, respectively. The percentage of HFP decreased during the first 20 h of hepatocytes in culture from preterm and term fetuses but not those from early newborns, in which the decrease occurred during the second day of culture. However, after 20 h in culture more than 80% of hepatocytes reached the G0/G1 phase, whatever the stage of development in which they were sown. This suggests that the observed changes in the fluorescence populations are not associated with the cell cycle; instead these changes mimic those observed during postnatal development and are therefore presumably due to mitochondrial differentiation.

Lipogenesis from lactate in rat neurons and astrocytes in primary culture

The rate of synthesis of phospholipid and sterol species from L-lactate in neurons and astrocytes in primary culture was studied. Both types of cells actively utilized lactate as lipid precursor, although the rate of lipogenesis was about 2-fold greater in astrocytes than in neurons. The incorporation of lactate into phospholipids was significantly higher than that into sterols in both types of cells, but the ratio of phospholipid/sterol synthesis was much higher in astrocytes than in neurons. Phosphatidylcholine (PC) was the main phospholipid synthesized in both types of cells, followed by phosphatidylethanolamine (PE), phosphatidylserine and phosphatidylinositol. No detectable synthesis of sphingomyelins was observed. The ratio of PC/PE synthesis was about 2-fold higher in astrocytes than in neurons. The main sterol synthesized in neurons was lanosterol, followed by desmosterol. However, the main sterol synthesized in astrocytes was desmosterol, followed by lanosterol and cholesterol. The different ratios of phospholipid/sterol and PC/PE synthesis found in neurons and astrocytes may result in different membrane fluidity being higher in astrocytes than in neurons. This may be associated with differences in the functionality of both types of cells.

Effect of valproate on lipogenesis in neonatal rat brain

The effect of valproate on lipogenesis in brain slices from early neonatal rats was studied. The rate of lipid synthesis from lactate and 3-hydroxybutyrate, but not from glucose, was decreased significantly by 1 mM valproate. Separation by high performance liquid chromatography of brain lipids showed that valproate inhibited the synthesis of major phospholipids (phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine) from lactate and major sterols (desmosterol, cholesterol and lanosterol) from lactate and 3-hydroxybutyrate. Valproate did not affect sterol synthesis but slightly enhanced phospholipid synthesis from glucose. However, the ratio of phosphatidylserine/phosphatidylethanolamine synthesis was decreased from lactate, glucose and 3-hydroxybutyrate, suggesting that valproate changes phospholipid composition of brain structures. These changes may contribute to the pharmacological action of the drug.

Evidence of stimulation of the gamma-aminobutyric acid shunt by valproate and E-delta 2-valproate in neonatal rat brain

The effect of valproate and its more active metabolite E-delta 2-valproate on the rate of glucose oxidation through different metabolic pathways in neonatal rat brain slices was studied. The presence of valproate or E-delta 2-valproate did not change the rate of [3,4-14C]glucose or [6-14C]glucose incorporation into CO2, suggesting that glucose oxidation through the pyruvate dehydrogenase-catalyzed reaction and through the tricarboxylic acid cycle was not affected by these drugs. However, both drugs significantly enhanced the rate of [2-14C]glucose oxidation, supporting the notion that the activity of the gamma-aminobutyric acid (GABA) shunt is specifically stimulated by valproate and, to a greater extent, by E-delta 2-valproate. The presence of methionine sulfoximine or gamma-hydroxybutyrate did not change the GABA shunt activity. Brain glutamate decarboxylase activity was significantly increased after incubation of the brain slices in the presence of valproate. Consequently, our results suggest that the mechanism of action of valproate is related to the increase in the levels of the inhibitory neurotransmitter GABA caused by the enhancement of flux through the glutamate decarboxylase-catalyzed reaction.

Lipogenesis from lactate in fetal rat brain during late gestation

Much evidence suggests that lactate may play a relevant role as a metabolic substrate for the brain immediately after delivery. In this work, the rate of lactate, glucose, and 3-hydroxybutyrate incorporation into CO2, phospholipids, and sterols was studied in fetal rat brain slices during the last 3 d of gestation. Lactate was the best substrate for the brain during the late gestation, not only as a source of energy, but also as precursor of brain phospholipids and sterols. The rates of oxidation and lipogenesis from glucose and 3-hydroxybutyrate showed a progressive decrease during the late gestation (10-15% reduction on d 20.5, p < 0.05, and 22-33% on d 21.5, p < 0.01, for oxidation; 14-18% on d 20.5, p < 0.05, and 20-22% on d 21.5, p < 0.05, for lipogenesis), whereas lactate maintained its rate of utilization in the same circumstances. The main phospholipid synthesized throughout the late gestation was phosphatidylcholine. The synthesis of phosphatidylcholine and phosphatidylethanolamine from lactate, glucose, and 3-hydroxybutyrate decreased during late gestation. Under these circumstances, however, the rate of phosphatidylserine synthesis from glucose was unchanged; it decreased from 3-hydroxybutyrate and increased from lactate. The rate of desmosterol synthesis was about 3- to 4-fold higher than those of cholesterol and lanosterol. Our results suggest that the capacity of fetal brain for lactate utilization remains high during late gestation, but the capacities for the utilization of glucose and 3-hydroxybutyrate decrease until term. This may indicate that lactate is an important substrate for brain development during late gestation.

Heterogeneity of L-alanine transport systems in brush-border membrane vesicles from rat placenta during late gestation

The placental uptake of L-alanine was studied by using purified brush-border membrane vesicles from rat trophoblasts. Saturation curves were carried out at 37 degrees C in buffers containing 100 mM (zero-trans)-NaSCN, -NaCl, -KSCN, -KCl, or -N-methyl-D-glucamine gluconate. The uncorrected uptake results were fitted by non-linear regression analysis to an equation involving one diffusional component either one or two saturable Michaelian transport terms. In the presence of NaCl, two distinct L-alanine transport systems were distinguished, named respectively System 1 (S-1; Vm1 about 760 pmol/s per mg of protein; KT1 = 0.5 mM) and System 2 (S-2; Vm2 about 1700 pmol/s per mg; KT2 = 9 mM). In contrast, in the presence of K+ (KCl = KSCN) or in the absence of any alkali-metal ions (N-methyl-D-glucamine gluconate), only one saturable system was apparent, which we identify as S-2. When Na+ is present, S-1, but not S-2, appears to be rheogenic, since its maximal transport capacity significantly increases in the presence of an inside-negative membrane potential, created either by replacing Cl- with the permeant anion thiocyanate (NaSCN > NaCl) or by applying an appropriate K+ gradient and valinomycin. alpha-(Methylamino)isobutyrate (methyl-AIB) appears to be a substrate of S-1, but not of S-2. For reasons that remain to be explained, however, methyl-AIB inhibits S-2. We conclude that S-1 represents a truly Na(+)-dependent mechanism, where Na+ behaves as an obligatory activator, whereas S-2 cannot discriminate between Na+ and K+, although its activity is higher in the presence of alkali-metal ions than in their absence (Na+ = K+ > N-methyl-D-glucammonium ion). S-2 appears to be fully developed 2 days before birth, whereas S-1 undergoes a capacity-type activation between days 19.5 and 21.5 of gestation, i.e. its apparent Vmax. nearly doubles, whereas its KT remains constant.

Developmental changes in rat liver mitochondrial populations analyzed by flow cytometry

Isolated rat liver mitochondria were split into three density fractions when applied to a Percoll gradient. This phenomenon is observable in the fetus, in the early newborn (1 h), in the suckling newborn (7 days), and in the adult, suggesting that the three density fractions coexist regardless of the state of development. The medium-density fraction sharply decreased immediately after delivery, being replaced by the high-density fraction. Flow cytometry analysis of mitochondrial density fractions stained with rhodamine 123 showed the occurrence in each density fraction and in all developmental states studied of two distinct mitochondrial populations with different fluorescence intensities. Our results suggest that the high-fluorescence population might be an immature form of mitochondria that decreases with the progression of development, coinciding with the postnatal enhancement of mitochondrial respiratory efficiency.

Carrier-mediated beta-D-hydroxybutyrate transport in brush-border membrane vesicles from rat placenta

Carrier-mediated beta-D-hydroxybutyrate transport in brush-border membrane (maternal-sided) vesicles prepared from trophoblast rat placenta was studied. The existence of a carrier-mediated transport system for beta-D-hydroxybutyrate in brush-border membrane vesicles was substantiated by the strong inhibitory effect of the protein modifier p-chloromercuriphenyl sulfonic acid and by the saturability of beta-D-hydroxybutyrate uptake as a function of beta-D-hydroxybutyrate concentration. beta-D-hydroxybutyrate uptake was stimulated by the presence of an inward-directed proton gradient but not by an inward-directed Na+ gradient. The mechanism for transport of beta-D-hydroxybutyrate seems to be a beta-D-hydroxybutyrate/H+ symport and not a beta-D-hydroxybutyrate/OH- antiport because beta-D-hydroxybutyrate transport was not sensitive to 4,4-diisothiocyano-2,2'-stilbenedisulfonic acid or furosemide. The Km, Vmax, and kd calculated by applying the iteration procedure to the data were 16 mM, 58 nmol.mg-1.10 s-1, and 0 nL.mg-1.s-1, respectively. The beta-D-hydroxybutyrate transport system might be shared by other monocarboxylic acids, and the carrier shows reversibility and exchange properties. There were no significant changes in the kinetic parameters of the beta-D-hydroxybutyrate transport system during the last 3 d of gestation. Nevertheless, there was a significant increase in the capacity of the beta-D-hydroxybutyrate transport system in brush-border membrane vesicles prepared from fasted pregnant rats, suggesting that the rise in maternal ketone body levels occurring as a consequence of maternal starvation is concurrent with the stimulation of the activity of the beta-D-hydroxybutyrate placental carrier to supply the fetus with ketone bodies.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of lactate in the rat brain during the early neonatal period

The metabolism of lactate in isolated cells from early neonatal rat brain has been studied. In these circumstances, lactate was mainly oxidized to CO2, although a significant portion was incorporated into lipids (78% sterols, 4% phosphatidylcholine, 2% phosphatidylethanolamine, and 1% phosphatidylserine). The rate of lactate incorporation into CO2 and lipids was higher than those found for glucose and 3-hydroxybutyrate. Lactate strongly inhibited glucose oxidation through the pyruvate dehydrogenase-catalyzed reaction and the tricarboxylic acid cycle while scarcely affecting glucose utilization by the pentose phosphate pathway. Lipogenesis from glucose was strongly inhibited by lactate without relevant changes in the rate of glycerol phosphate synthesis. These results suggest that lactate inhibits glucose utilization at the level of the pyruvate dehydrogenase-catalyzed reaction, which may be a mechanism to spare glucose for glycerol and NADPH synthesis. The effect of 3-hydroxybutyrate inhibiting lactate utilization only at high concentrations of 3-hydroxybutyrate suggests that before ketogenesis becomes active, lactate may be the major fuel for the neonatal brain. (-)-Hydroxycitrate and aminooxyacetate markedly inhibited lipogenesis from lactate, suggesting that the transfer of lactate carbons through the mitochondrial membrane is accomplished by the translocation of both citrate and N-acetylaspartate.

Ketogenesis from lactate in rat liver during the perinatal period

Lactate, which accumulates in neonatal plasma during the first hours after delivery, is used by neonatal tissues as a source of energy and carbon skeleton. In this work, lactate use by rat liver during late gestation (last 3 d) and early neonatal life (6 h postpartum) has been studied. The rate of lactate use by liver was compared with that found with oleate, inasmuch as fatty acids are the main substrates for the liver after the onset of lactation. The main fate of lactate in the liver during the perinatal period was ketone bodies, preferentially over CO2 and lipids. The rate of oxidation of lactate and its incorporation into lipids decreased during late gestation, but the rate of ketogenesis from lactate remained high during this period. After birth, the rate of lactate oxidation sharply increased, but lipogenesis decreased and ketogenesis was maintained. The rates of oleate oxidation and ketogenesis from oleate were two orders of magnitude lower than those from lactate. However, the rate of oleate incorporation into lipids was only 4-fold lower than that observed from lactate under the same circumstances. Our results suggest that lactate is a major substrate for the liver during the perinatal period because it is mainly incorporated into ketone bodies. This may target lactate carbons to different neonatal tissues.

Lactate utilization by isolated cells from early neonatal rat brain

The utilization of lactate, glucose, 3-hydroxybutyrate, and glutamine has been studied in isolated brain cells from early newborn rats. Isolated brain cells actively utilized these substrates, showing saturation at concentrations near physiological levels during the perinatal period. The rate of lactate utilization was 2.5-fold greater than that observed for glucose, 3-hydroxybutyrate, or glutamine, suggesting that lactate is the main metabolic substrate for the brain immediately after birth. The apparent Km for glucose utilization suggested that this process is limited by the activity of hexokinase. However, lactate, 3-hydroxybutyrate, and glutamine utilization seems to be limited by their transport through the plasma membrane. The presence of fatty acid-free bovine serum albumin (BSA) in the incubation medium significantly increased the rate of lipogenesis from lactate or 3-hydroxybutyrate, although this was balanced by the decrease in their rates of oxidation in the same circumstances. BSA did not affect the rate of glucose utilization. The effect of BSA was due not to the removal of free fatty acid, but possibly to the binding of long-chain acyl-CoA, resulting in the disinhibition of acetyl-CoA carboxylase and citrate carrier.

Carrier-mediated L-lactate transport in brush-border membrane vesicles from rat placenta during late gestation

The mechanism for L-lactate transport across microvillous membrane vesicles prepared from rat placenta was examined. Uptake of L-lactate into these vesicles was mainly the result of transport into the intravesicular (osmotically active) space. The initial rate of L-lactate uptake was not affected by the presence of an inward gradient of either Na+ or K+. In the presence of an inward-directed proton gradient, L-lactate uptake was markedly stimulated, accumulating at concentrations 6-7-fold higher than the equilibrium. Lower transmembrane pH gradients were associated with slower initial uptakes and smaller overshoots. L-Lactate uptake determined under an inside-directed pH gradient was strongly inhibited by p-chloromercuriphenylsulphonic acid, a protein-thiol oxidizing agent. L-Lactate uptake was: (1) saturable as a function of the concentration of L-lactate, (2) inhibited by monocarboxylic acids such as pyruvate, D-lactate, beta-hydroxybutyrate and alpha-cyano-4-hydroxycinnamic acid, and (3) temperature-dependent. When present inside the vesicles, L-lactate, pyruvate and beta-hydroxybutyrate caused trans-stimulation of L-lactate uptake both in the presence and in the absence of an inside-directed pH gradient, indicating that L-lactate transport is a reversible process that can be shared by other monocarboxylic acids. There were no significant changes in maximal initial rate or in the kinetic parameters of L-lactate transport during the last 3 days of gestation.

Inhibition of sterol but not fatty acid synthesis by valproate in developing rat brain in vivo

The effect of administration of valproate on lipogenesis in the developing rat brain in vivo was studied. Valproate inhibited by 21-38% the rate of 3H2O incorporation into brain sterols, without significantly affecting fatty acid synthesis. Similarly, R-[2-14C]mevalonate incorporation into sterols was inhibited by 33-54%; the low rate of fatty acid synthesis under these conditions was not affected by valproate. Plasma ketone bodies decreased after treatment with valproate. Valproate inhibited (about 50%) both sterol and fatty acid synthesis in livers of weanling rats. It is concluded that valproate can specifically inhibit sterol synthesis in the brain during development, in part at a stage after mevalonate formation, and also by decreased exogenous precursor supply.

Effect of streptozotocin-induced diabetes on sex differences in biliary lipid secretion in the rat

Diabetes mellitus is often associated with lipid abnormalities that may differ with sex. In this work we studied biliary lipid secretion in male and female anaesthetized Wistar rats (250 g). Diabetes was induced by a single intraperitoneal injection of streptozotocin (6 mg/100 body weight) 6 days before carrying out the studies on bile secretion. Our results confirm the existence of sex differences in bile formation and composition, most of them probably due to a higher (+27%) bile acid output in the female animals. Diabetes induced profound alterations in these sex differences. (a) Bile flow was reduced in both sexes, but more markedly so in female diabetic rats; thus the difference observed in healthy animals was reduced (from 2.22 to 1.58 and from 1.84 to 1.40 microliters/min per g liver in female and male rats, respectively). (b) Bile acid and phosphatidylcholine outputs were increased to a similar extent (bile acid output: from 46.7 to 55.8 nmol/min per g liver, in females and from 36.8 to 50.7 nmol/min per g liver, in males; phosphatidylcholine output: from 3.3 to 13.1 nmol/min per g liver, in females and from 4.5 to 12.5 nmol/min per g liver, in males), and hence the sex differences were abolished. (c) Cholesterol output was increased in both sexes, but this enhancement was significantly higher in female rats (from 0.75 to 1.31 and from 0.65 to 0.89 nmol/min per g liver, in females and males, respectively). (d) The fractional pool of phospholipid species secreted into bile was different in female compared with male rats. The percentage of phosphatidylcholine was higher in female than in male healthy rats. Streptozotocin treatment reversed this proportion, which suggests that changes in the phospholipid composition of the canalicular plasma membrane may play a role in the observed alterations in biliary lipid secretion during diabetes mellitus. Most of the above-described streptozotocin-induced changes were prevented by insulin replacement from the 3rd to the 6th days after streptozotocin injection. In summary, the present study describes alterations in sex differences in biliary lipid secretion of streptozotocin-induced diabetes. These changes are dependent on the insulin deficiency state rather than on a direct hepatotoxicity of the diabetogenic drug.

Metabolic effects of the delay in obliteration of the umbilical cord in the newborn rat

The effect of delay in obliteration of the umbilical cord on the time-courses of liver glycogen, blood glucose and lactate concentrations and blood PO2, PCO2 and pH during the first 6 h of extrauterine life were studied. Obliteration of the umbilical cord 2 h after delivery resulted in an increase in liver glycogenolysis without significantly affecting the other parameters studied. A 6-hour delay in obliteration of the umbilical cord increased lactiacidemia and decreased blood PO2 and pH without significantly affecting the other parameters studied. A supply of pure oxygen to the newborns decreased lactiacidemia and increased PO2, although the differences between obliterated and nonobliterated newborns remained. These results suggest that hypoxia due to the persistence of placental circulation results in an increase in lactiacidemia as a consequence of a decrease in lactate utilization.