Effect of postnatal hypoxia on ammonia metabolism during the early neonatal period in the rat

The effect of experimental hypoxia on blood glutamine, glutamate, urea, ammonia, allantoin, hypoxanthine, xanthine, urate, orotate and lactate concentrations and on PO2, PCO2 and pH in term delivered newborn rats during the first 4 h after delivery were studied. Hypoxia increased blood glutamine, glutamate, allantoin and 'xanthines' (hypoxanthine + xanthine + uric acid) concentrations but decreased blood urea and ammonia concentrations. These results suggest that hypoxia inhibited ureogenesis by decreasing the ammonia available for urea synthesis.

Identification by flow cytometry of two distinct rhodamine-123-stained mitochondrial populations in rat liver

Isolated rat liver mitochondria were split into three fractions of increasing density when applied to a Percoll gradient. NADH-ubiquinone oxidoreductase, succinate dehydrogenase and cytochrome-c oxidase but not F1-ATPase activities increased with density as well as respiratory rate in state 3 and the respiratory control index. Flow cytometry of mitochondrial density fractions stained with rhodamine-123 revealed the occurrence in each density fraction of two distinct mitochondrial populations with different fluorescence intensity. The high fluorescence population was minor and its proportion decreased with density. The extent of high fluorescence population staining depended on the deenergized state of the mitochondria suggesting that this population represents an immature form of the mitochondria which may develop into a fully functional organelle by the incorporation of structural and/or functional proteins.

Ammonia metabolism during the suckling period in the rat

1. The time-courses of blood glutamine, glutamate, alanine, ammonia, urea and allantoin concentrations during the first 15 days of extrauterine life were studied. 2. Glutamine and glutamate concentrations followed the same pattern and correlated positively, suggesting that both amino acids are utilized or released synchronously. 3. Alanine concentrations decreased during the first 3 days, reaching levels close to those of adults which persisted up to the end of the observation period. 4. A highly significant correlation was found between ammonia and urea concentrations, suggesting that during the suckling period urea synthesis may be limited by blood ammonia availability. 5. The time-course of allantoin concentrations suggests that the synthesis of purines was enhanced during the first day, decreasing sharply during the 2nd to steeply increase to the end of the suckling period.

Maternal-fetal relationship in ammonia metabolism during late gestation in the rat

The concentrations of the major metabolites for nitrogen excretion and/or transport in maternal and fetal blood and amniotic fluid during the last 2 days of gestation were investigated. Alanine, glutamine, ammonia and allantoin accumulated in amniotic fluid during late gestation. Urea concentrations increased in amniotic fluid though only during the last day of gestation, suggesting that urea is taken up by the mother through the amniotic membranes. Glutamate did not accumulate in amniotic fluid during late gestation although high concentrations of it were found in fetal blood in the same circumstances, suggesting the occurrence of a mechanism for preventing fetal glutamate disposal.

Changes in biliary secretion and lactate metabolism induced by diethyl maleate in rabbits

Diethyl maleate is a compound which binds with glutathione by means of a glutathione S-transferase and is excreted into bile leading to a rapid depletion of hepatic glutathione. In the rabbit, the activity of the enzyme is fairly low and we were thus prompted to study the possible effects of diethyl maleate on biliary secretion and metabolic status in this species. The administration of diethyl maleate induced a transient choleresis followed by cholestasis. The choleresis coursed with increases in the biliary output of sodium and unaccounted anions, whereas those of chloride, bicarbonate and bile acids were unaffected. Our data seem to confirm that choleresis is due to the osmotic activity of diethyl maleate compounds excreted into bile, as has been reported in rats and dogs. The cholestasis observed coursed with falls in the outputs of sodium, chloride and bicarbonate though that of bile acids remained constant. Following diethyl maleate administration, a metabolic acidosis appeared with progressive increases of blood lactate concentration. In bile the concentration of this anion closely followed that of plasma. The cholestasis is attributed to a lowered biliary secretion of bicarbonate probably secondary to the metabolic alteration. The hepatic values of cytoplasmatic and mitochondrial NADH/NAD ratios and of adenine nucleotide concentrations suggest that the increase in blood lactate results rather from a fall in its hepatic utilization that from an increase in its production.

Lactate utilization by the neonatal rat brain in vitro. Competition with glucose and 3-hydroxybutyrate

The maximum rates of lactate oxidation and lipogenesis from lactate by early-neonatal brain slices were considerably greater than those for utilization of glucose and 3-hydroxybutyrate at physiological concentrations. Lactate inhibited glucose utilization, but enhanced 3-hydroxybutyrate utilization. 3-Hydroxybutyrate inhibited lactate and glucose utilization. Glucose slightly inhibited oxidation of lactate and 3-hydroxybutyrate, but scarcely enhanced lipogenesis from these substrates.

Attenuation of postnatal hypoxia in the premature newborn rat by maternal treatment with dexamethasone: its relationship with lung phospholipid content

The effect of maternal treatment with dexamethasone on blood PO2, PCO2, pH and lactate concentrations and on lung phospholipid content in premature newborn rats during the early neonatal period was studied. The postnatal hypoxia shown by premature newborn rats was prevented by this treatment. Postnatal hypercapnia was longer in premature newborns showed significantly lower lung phospholipid concentrations than term-delivered newborn animals. Maternal treatment with dexamethasone increased lung phospholipid concentrations which reached values close to those found in term newborns. Our results suggest that maternal treatment with dexamethasone prevents postnatal hypoxia in the premature newborn rat by increasing the lung phospholipid content, which results in an enhancement of oxygen transfer through the alveolar membranes and the attenuation of hyperlactiacidemia.

The role of lactate as an energy substrate for the brain during the early neonatal period

The role played by lactate as an energy substrate for the newborn rat during the early neonatal period was studied. Plasma lactate is mostly removed within the first 2 h after delivery, i.e. during the presuckling period. Lactate removal was enhanced by hyperoxia but strongly inhibited by hypoxia, showing a direct correlation with blood oxygen concentrations. Lactate was not converted into glucose during the presuckling period, gluconeogenesis being insignificant in these circumstances; instead it was rapidly oxidized through the tricarboxylic acid cycle. Likewise, lactate was significantly oxidized by brain slices from newborns at birth. At physiological concentrations, lactate oxidation by brain slices was 10- and 3-fold higher than that of glucose and 3-hydroxybutyrate, respectively. In the same circumstances, lipogenesis de novo from lactate was 2- and 5-fold higher than from glucose and 3-hydroxybutyrate, respectively. The results suggest that lactate is the main metabolic fuel for the brain during the early neonatal period.

Regulation of lipogenesis in vivo by glucose availability and insulin secretion in maternal and foetal tissues during late gestation in the rat. Effect of glucose intubation, streptozotocin-induced diabetes and starvation

Administration of an oral load of glucose did not change the rate of lipogenesis in maternal liver during late gestation. However, streptozotocin-induced diabetes or starvation decreased maternal liver lipogenesis at 20-22 days of gestation. Glucose intubation, on the other hand, increased foetal lipogenesis at 21-22 days. In addition, maternal starvation decreased foetal lipogenesis and plasma insulin concentration. However, chronic hyperglycaemia induced by streptozotocin administration to the mother did not change foetal liver lipogenesis.

The role of ATP/ADP ratio in the control of hepatic gluconeogenesis during the early neonatal period

The hepatic ATP/ADP ratio showed significant changes during the first day of postnatal life in starved newborn rats. The occurrence of a positive linear correlation between the ATP/ADP ratio and the gluconeogenic capacity in vivo is reported in the newborn rat during the first day of life.

Lactate as an oxidizable substrate for rat brain in vitro during the perinatal period

Foetal brain slices showed a high capacity for lactate oxidation in vitro during late gestation. This capacity remained high during the very early postnatal period, suggesting that lactate may play an important role as an energy substrate in the brain during the early neonatal period. The capacity for lactate oxidation decreased markedly during the first 2 days of extra-uterine life and thereafter remained low.

Postnatal hypoglycaemia and gluconeogenesis in the newborn rat. Delayed onset of gluconeogenesis in prematurely delivered newborns

The concentrations of glucose and lactate in the blood and of liver glycogen, and the phosphoenolpyruvate carboxykinase activity in liver and kidney of term and preterm newborn rats, were studied during the first 6 h post partum. Rates of lactate turnover and gluconeogenesis in vivo from [U-14C]lactate at 3 h and 6 h post partum were also quantified. The development of the prolonged postnatal hypoglycaemia observed after birth in the premature newborn rat is associated with lower rates of glucose production through glycogenolysis and gluconeogenesis; liver glycogenolysis was the main contributing factor to the glucose available during the neonatal period studied in both groups. Delayed induction of liver phosphoenolpyruvate carboxykinase activity was observed in premature newborn rats. Renal phosphoenolpyruvate carboxykinase activity increased 72% from birth in preterm newborns, but only a 25% increase was found in term newborns during the same experimental period. The gluconeogenesis in vivo from [U-14C]lactate paralleled the appearance of cytosolic phosphoenolpyruvate carboxykinase activity in the liver of both groups of newborns. Blood lactate concentrations remained higher in preterm than in term newborns. The postnatal utilization of lactate via the gluconeogenic pathway in either group of newborns was always less than 20% of the total lactate used. The results presented are discussed in relation to the development of postnatal hypoglycaemia and gluconeogenesis in the premature newborn rat.

Isozymes of lactate dehydrogenase in fetal rat liver. Their correlation with blood oxygen concentrations

The percentages of lactate dehydrogenase (EC 1.1.1.27) isozyme 4 (LDH4) was twice that of LDH5 in fetal rat liver on day 17 of gestation. The proportion of LDH5 and LDH4 reached approximately the same percentage (46% of each) on days 17-20 of gestation. On day 21, the percentage of LDH4 increased sharply at the expense of LDH5. Fetal blood oxygen concentrations increased on day 21 of gestation, but decreased later near parturition. Positive and negative linear correlations occurred during late gestation between concentrations of blood oxygen and LDH4 and LDH5 activities, respectively. These results suggest that the proportion of LDH5 and LDH4 in fetal rat liver may vary according to the amount of oxygen available to the tissue.

Effect of postnatal hypoxia on the energy homeostasis of the newborn rat during the early neonatal period

Newborn rats breathing a low-oxygen mixture showed similar rates of glycogenolysis to newborns breathing air. However, hypoxia prevented the decrease of plasma glucose and lactate concentrations which occurred in newborns breathing air immediately after delivery. The time-course of plasma alanine was not affected by experimental hypoxia. The decrease in the liver lactate/pyruvate ratio observed in control newborns immediately after delivery was prevented by hypoxia. Lower blood oxygen concentrations were observed in hypoxic animals throughout the observation period. Lower ATP concentrations were observed in hypoxic newborns during the first hour after delivery but similar values were observed in both groups thereafter.

Relationship between lipogenesis and glycogen synthesis in maternal and foetal tissues during late gestation in the rat. Effect of dexamethasone

Treatment with dexamethasone enhanced 3H2O incorporation into liver and blood lipid, and also increased plasma glucose, insulin, non-esterified fatty acid and triacylglycerol concentrations during late gestation in the mother rat. An inverse relationship between glycogen and lipid synthesis in foetal liver and lung was observed in control rats. This relationship was also observed in foetal liver, but not in foetal lung, after treatment with dexamethasone.

Adenine nucleotide concentrations in liver of fetal rats. Neonatal changes in the premature newborn

Changes in ATP, ADP and AMP concentrations in the liver in term and preterm newborns during the perinatal period have been studied. Fetal liver ATP concentrations decreased during the penultimate day of gestation and remained low during the last day of pregnancy. ATP concentrations sharply increased in the liver of term newborns immediately after delivery, remaining unchanged after 1 h of extrauterine life. High ATP concentrations were observed in the liver of preterm newborns at delivery without changes within the early postnatal period. No significant changes in liver ADP and AMP concentrations were observed in either group throughout the observation period. Energy charge was higher in preterm liver at delivery but similar values were reached in term liver after 30 min of extrauterine life. These results suggest that the energy stage of the preterm liver is high at delivery without changes during the early postnatal period.

Stimulation of ketogenesis by propionate in isolated rat hepatocytes: an explanation for ketosis associated with propionic acidaemia and methylmalonic acidaemia?

The effect of propionate on ketone body production from oleate and octanoate in isolated rat hepatocytes was studied. Propionate (5 mmol/l) stimulated ketogenesis from oleate and octanoate, although the effect was more pronounced when octanoate was used as substrate. Propionate decreased CO2 production from fatty acids, suggesting that propionate inhibited the oxidation of free fatty acid carbons through the tricarboxylic acid cycle. Our results suggest that propionate enhanced ketogenesis as a consequence of the decrease in the rate of the tricarboxylic acid cycle, caused by propionate and/or its derivatives. The stimulation of ketogenesis caused by propionate is discussed as the possible cause of ketosis associated with propionic acidaemia and methylmalonic acidaemia.

Lipogenesis in vivo in maternal and foetal tissues during late gestation in the rat

The rate of 3H2O incorporation into lipid in vivo progressively decreased in liver but increased in parametrial adipose tissue during the last 3 days of gestation. These changes seem to be related to those occurring in plasma insulin and progesterone concentrations during the same period. Foetal liver showed a high rate of lipogenesis, which sharply decreased before parturition. foetal lung lipogenesis increased during days 20 and 21 of gestation.

Antiketogenic effect of gluconeogenic substrates. II. Effect of pyruvate

The effect of pyruvate on the fate of free fatty acids in isolated hepatocytes from starved rats has been studied. 5 mM pyruvate inhibited ketone bodies production variously from endogenous substrates, acetate, octanoate and oleate. However, the incorporation of radioactivity into ketone bodies from acetate, octanoate or oleate was not affected by the presence of pyruvate. The oxidation of radioactive fatty acids to CO2 was increased by the presence of pyruvate. These results suggest that pyruvate inhibited ketogenesis by increasing the rate of the tricarboxylic acid cycle.

Regulation of glycogenolysis in the liver of the newborn rat in vivo. Inhibitory effect of glucose

Newborn rats were injected immediately after delivery with glucose or glucose plus mannoheptulose, and the time-courses of liver glycogen, plasma glucose insulin and glucagon concentration were studied. The administration of glucose prevented both liver glycogenolysis and the increase in plasma glucagon concentration, which normally occurs immediately after delivery. In addition, the administration of glucose prevented the decrease of plasma glucose and insulin concentration which normally occurs during the first hour of extrauterine life. Supplementation of glucose with mannoheptulose prevented the increase of plasma insulin concentrations caused by the administration of glucose; liver glycogenolysis, however, was not stimulated in these circumstances. The increase in the rate of glycogenolysis caused by the administration of glucagon was prevented in newborn rats previously treated with glucose. These results suggest that glucose exerts an inhibitory effect on the stimulation of neonatal liver glycogenolysis by glucagon.

Prematurity in the rat. III. Effect of oxygen supply

Changes in liver glycogen, plasma glucose, lactate, alanine and glycerol concentrations in term and preterm newborn rats breathing pure oxygen have been studied. The time courses of lactate and pyruvate concentrations in the livers of term and preterm rats breathing air or pure oxygen have also been investigated. The increased oxygen supply enhanced plasma glucose, lactate and alanine utilization while the rate of glycogenolysis was not effected. In these conditions, the resistance to lactate utilization observed in preterm newborns breathing air was overcome. The liver lactate/pyruvate ratio sharply decreased immediately after delivery in term and preterm rats breathing pure oxygen and in term rats breathing air. However, this decrease was delayed for 30 min in preterm newborns breathing air. These results suggest that the preterm rat suffers a defective oxygen supply to the tissues which results in a transient resistance to lactate utilization.

Effect of gluconeogenic substrates on ketogenesis in isolated rat hepatocytes. I. Effect of glycerol

The effect of glycerol on the rate of free fatty acids in isolated hepatocytes from starved rats has been studied. 5 mM glycerol inhibited the ketone bodies production from endogenous substrates, acetate, octanoate or oleate. The incorporation of radioactivity into ketone bodies from acetate, octanoate or oleate was also inhibited by glycerol. The oxidation of radioactive fatty acids to CO2 was not significantly changed by glycerol. However, the incorporation of acetate, octanoate or oleate carbons into liver lipids were increased by glycerol.