Elizabeth M. Jones

Reduced brain glucose with normal plasma glucose in salicylate poisoning

After the intraperitoneal injection into young mice of 700-800 mg/kg of salicylate, brain glucose fell to one-third or less of control values despite normal plasma glucose levels; brain lactate was nearly doubled and there were small decreases in phosphocreatine (18%) and in glycogen (17%). ATP, pyruvate, alpha-ketoglutarate, and glutamate were unchanged. In liver, glycogen was reduced 79% and lactate was five times higher than in control animals; glucose, glucose-6-phosphate, and ATP were unchanged. Since salicylate uncouples oxidative phosphorylation, it is postulated that high energy phosphate in the brain is maintained near normal levels by a compensatory increase in cerebral glycolysis. Apparently the brain glucose level falls because the rate of utilization exceeds the rate at which glucose can be supplied from the blood. Concurrent administration of glucose with salicylate elevated brain glucose concentration and was associated with striking improvement in the condition and the increased survival of the animals. These findings stress the fact that in salicylate poisoning the supply of glucose to the brain may be inadequate even when blood glucose levels are normal.

THE EFFECTS OF ANOXIA UPON ENERGY SOURCES AND SELECTED METABOLIC INTERMEDIATES IN THE BRAINS OF FISH, FROG AND TURTLE

The levels of the main cerebral energy reserves, ATP, P‐creatine, glycogen and glucose, and of several glycolytic intermediates and lactate, were measured in the brains of fish (Carassius auratus), turtle (Pseudemys scripta elegans) and frog (Rana pipiens). The levels of glycogen in these brains were 2‐9 times higher than those reported for mammals. In frog, cerebral glycogen levels were 35 per cent higher during the winter than in spring. The P‐creatine: ATP ratios were 3 instead of the more usual (mammalian) value of 1. The levels of other intermediates were similar to those found in mammalian brain.

EFFECTS OF SALT AND WATER LOADING ON CARBOHYDRATE AND ENERGY METABOLISM AND LEVELS OF SELECTED AMINO ACIDS IN THE BRAINS OF YOUNG MICE

—This is a report of the effect of extreme changes in plasma sodium concentration induced by chronic (5 d) water deprivation and hypertonic saline injections and acute (4 h) overhydration with hypotonic glucose or fructose on the water and electrolyte content and levels of selected metabolites in the brains of young mice. In the dehydrated hypernatremic mice (plasma Na+, 186 × 3 mequiv./1) significant increases were found in brain glucose (82%), alanine (16%), aspartate (45%), glutamate (19%), gamma‐amino butyrate (34%) and glutamine (42%) concentrations. In striking contrast, water‐intoxicated mice (plasma Na+, 110 × 4 mequiv./1) had significantly decreased levels of alanine (17%), aspartate (38%) and glutamate (33%). Significant reductions in brain lactate (30–40%) and malate concentrations (23%) in both groups of experimental mice are suggestive of reduced cerebral metabolic rate.

OXIDIZED AND REDUCED PYRIDINE NUCLEOTIDE LEVELS AND ENZYME ACTIVITIES IN BRAIN AND LIVER OF NIACIN DEFICIENT RATS

ADVANTAGE has been taken of the recent development of highly sensitive methods (LOWRY, PASSONEAU, SCHULZ and ROCK, 1961) to study the response of the individual pyridine nucleotides (NADf, NADH, NADP+, NADPHg) in the brain andliver of rats to a low tryptophan, niacin-free diet. The study of three pyridine nucleotide-dependent enzymes was included, prompted by the findings of BURCH et al. (1956,1960) that some flavin-dependent enzymes decrease in riboflavin deficiency. SINGAL, SYDENSTRICKER and LITTLEJOHN (1 948) measured the nicotinic acid levels in different tissues of rats on corn rations and found them to be subnormal in the brain, liver, and muscle of the deficient animals but normal in other tissues. BURCH et al. (1955) reported that rats fed low amounts of tryptophan and niacin had subnormal amounts of oxidized pyridine nucleotides in blood cells and liver. More recently, SPIRTES and ALPER (1 961) studied the diphosphopyridine nucleotide levels in the livers of niacin-deficient and protein-deficient mice. They found a decrease of both NAD+ and NADH in the liver of the niacin-deficient animals, with no change in the NAD+/NADH ratio.

Femoral-based central venous oxygen saturation is not a reliable substitute for subclavian/internal jugular-based central venous oxygen saturation in patients who are critically ill.

BACKGROUND Central venous oxygen saturation (Scv(O(2))) has been used as a surrogate marker for mixed venous oxygen saturation (Sv(O(2))). Femoral venous oxygen saturation (Sfv(O(2))) is sometimes used as a substitute for Scv(O(2)). The purpose of this study is to test the hypothesis that these values can be used interchangeably in a population of patients who are critically ill. METHODS We conducted a survey to assess the frequency of femoral line insertion during the initial treatment of patients who are critically ill. Scv(O(2)) vs Sfv(O(2)) STUDY: Patients with femoral and nonfemoral central venous catheters (CVCs) were included in this prospective study. Two sets of paired blood samples were drawn simultaneously from the femoral and nonfemoral CVCs. Blood samples were analyzed for oxygen saturation and lactate. RESULTS One hundred and fifty physicians responded to the survey. More than one-third of the physicians insert a femoral line at least 10% of the time during the initial treatment of patients who were critically ill. Scv(O(2)) vs Sfv(O(2)) STUDY: Thirty-nine patients were enrolled. The mean Scv(O(2)) and Sfv(O(2)) were 73.1% +/- 11.6% and 69.1% +/- 12.9%, respectively (P = .002), with a mean bias of 4.0% +/- 11.2% (95% limits of agreement: -18.4% to 26.4%). The mean serum lactate from the nonfemoral and femoral CVCs was 2.84 +/- 4.0 and 2.72 +/- 3.2, respectively (P = .15). CONCLUSIONS This study revealed a significant difference between paired samples of Scv(O(2)) and Sfv(O(2)). More than 50% of Scv(O(2)) and Sfv(O(2)) values diverged by > 5%. Sfv(O(2)) is not always a reliable substitute for Scv(O(2)) and should not routinely be used in protocols to help guide resuscitation.

Decrease and Inhibition of Liver Glycogen Phosphorylase After Fructose: An Experimental Model for the Study of Hereditary Fructose Intolerance

Inhibition of liver phosphorylase may play an important role in the fructose-induced hypoglycemia of hereditary fructose intolerance. This report is an in vivo study of the effects of fructose on selected metabolic intermediates and on phosphorylase activity in the liyers of young mice. Phosphorylase activity in liver homogenate was measured in the direction of glycogen breakdown. The Km for Pi was 1.12 mM and the Ki for fructose-1-phosphate was 1.19 mM. This finding is particularly relevant since twenty minutes after fructose injection (30 mmoles per kilogram intraperitoneally) liver Pi was reduced 50 per cent, p < 0.001 and fructose-1-phosphate was increased fifty fold, p < 0.001. Liver glucose was unchanged. In controls, activity of phosphorylase was dependent on the state of the animals: 2.43 ± 0.31 μ/moles/gm. min−1 in anesthetized mice, 9.55 ± 0.55 in excited animals. Under these same conditions phosphorylase activity in fructose-injected littermates was reduced 40 to 80 per cent (mean 48 per cent, p = 0.002). At the concentrations of Pi and fructose-1-phosphate found in liver after fructose, phosphorylase activity in vitro was inhibited 88 per cent (p < 0.001). In vivo the activity of liver phosphorylase is apparently reduced by two mechanisms, a conversion to the inactive form and an inhibition of the remaining active enzyme by reduced Pi and elevated fructose-1-phosphate levels. We have postulated that de novo synthesis of glucose from fructose in normal animals could mask any hypoglycemia which might result from reduced liver phosphorylase activity. The in vivo effect of glucose injection on liver phosphorylase was also studied. At high levels of enzyme activity, glucose reduced phosphorylase activity by 43 per cent, p = 0.012; at low levels of enzyme activity, glucose had no effect.

Decrease in Brain Glucose in Anoxia in Spite of Elevated Plasma Glucose Levels

Extract: Anoxia was produced in 34 mice less than 12 hr of age by exposure to N2 at 37° (Po2 less than 5 mm Hg). Although brain glucose levels fell from the normal value of 0.60 ± 0.14 mmol/kg to 0.22 ± 0.04 mmol/kg after 6 min of anoxia, in the livers of the same animals there was a fourfold increase in glucose concentration from 2.61 ± 0.28 mmol/kg to 10.45 ± 0.45. In 22 other animals of the same age plasma glucose levels increased from 3.04 ± 0.03 mm to 5.56 ± 1.09 mm during this interval of anoxia. Further studies concerned the mechanism of this unexpected independence of blood and brain glucose values during anoxia.During the 6 min of anoxia brain lactate increased 7.49 mmol/kg. This increase is more than twice that accounted for by the total decrease in brain glucose and glycogen. One explanation for this finding is an increased uptake of glucose from the blood by the brain. If so, the rate of glucose influx is almost 5 times that reported for newborn mice with an adequate O2 supply. Another possibility is a transport or diffusion of lactate from the blood to the brain. However, a study of the effect of lactate administration on levels of lactate in plasma and brain of 17 newborn mice suggests that permeation of the blood-brain barrier to lactate is a less likely explanation. Inasmuch as glycolysis increases 10-fold in ischemic brain of the neonatal mouse, it appears that brain glucose decreases in these animals because the demand for glucose during anoxia exceeds the supply.Speculation: In experimental animals levels of glucose in plasma are not always an accurate reflection of glucose levels in the brain. This is the case in anesthesia, after chronic administration of hydrocortisone, and in acute salicylate poisoning. The present study is another example of this paradox. During 6 min of anoxia, brain glucose in newborn mice fell 72% despite a doubling of the concentration of glucose in plasma. Because it is generally accepted that a decrease in the brain glucose reserve is potentially serious, it is important to recognize that a normal or even increased blood sugar need not signify adequate cerebral glucose levels. Furthermore, there is some evidence to suggest that, under these circumstances, the administration of glucose may be life saving.

Permeability of the blood-brain barrier to fructose and the anaerobic use of fructose in the brains of young mice.

—Fructose levels were determined in plasma and brain of 8‐ to 12‐day‐old mice at intervals after the injection of 30 mmol/kg intraperitoneally; controls received NaCl, 15 mmol/kg. In normal animals brain fructose increased very slowly despite a rapid rise in plasma levels (120 times the control value in 5 min). At 40 min the cerebral level was 1.54 ± 0.23 mmol/kg; the corresponding plasma level was 47.1 ± 4.8 mM. The data suggest that fructose can serve as a source of energy to the brain in times of critical need: during insulin hypoglycemia brain fructose increased to only 0.88 ± 0.05 mmol/kg during the same interval (40 min) despite plasma fructose values equal to those in control animals; also 30 s after cerebral ischemia (decapitation) brain fructose fell from a zero time value of 1.19 ± 0.09 mmol/kg (20 min after fructose injection) to 0.76 ± 0.06 mmol/kg (P= 0.005). Under both circumstances (hypoglycemia and ischemie anoxia) an apparent threshold concentration of fructose for utilization was observed—0.6–0.7 mmol/kg. The most likely explanation for this finding appears to be that this level of fructose was in the extracellular space of the brain. Hexokinase activity in brain homogenates of 8‐ to 12‐day‐old mice with fructose and ATP at concentrations found in vivo and during ischemie anoxia did not appear to be rate‐limiting. We concluded that the major handicap to the use of fructose by the brain was the limited penetration of fructose from the blood to the brain.

Recovery time and sensorimotor cortex lesion effects

Rats received one-stage, bilateral lesions of the individual sensorimotor cortex areas (Sm-1, Sm-2) and were compared to sham operated rats or rats with lesions of Sm1 + 2 in learning a series of 5 ridge-smooth tactile discriminations. Some rats began testing 1 or 2 weeks after surgery, while others remained in their home cages for 1 month, 6 months, 1 year or 2 years before beginning testing. The rats with combined Sm1 + 2 lesions performed very poorly regardless of recovery time, and those with sham operations performed extremely well even when tested late in life. The animals with either Sm-1 or Sm-2 lesions did not do well after the shorter recovery periods, but obtained scores within the sham operated group range when given 1 year. (Sm-2) or 2 years (Sm-1) for recovery. These data show that spared parts of the damaged system are important in mediating tactile discriminative behavior. However, the reasons for the long delays in recovery are not clear.

Decrease and inhibition of liver phosphorylase (LP) after fructose: An experimental model for the study of hereditary fructose intolerance (HFI)

It has been postulated that inhibition of LP plays a significant role in the fructose-induced hypoglycemia of HFI. To test this hypothesis weanling mice were injected i.p. with 30 m-moles/kg of fructose or saline of equal osmolality. Although liver glucose levels did not fall the findings are relevant to the understanding of the pathophysiology of HFI. 20 min after fructose injection, fructose and fructose-1-P (F-1-P) levels were 21.4 ± 2.9 and 10.6 ± 0.9 m-moles/kg respectively. ATP and Pi were reduced 50%, to 1.36 m-moles/kg and 2.07 m-moles/kg, p = 0.001. At the same time LP was reduced 48% (p = 0.002). This finding suggest a shift to the inactive form of the enzyme. To mimic the in vivo situation LP in normal liver homogenate was measured in the presence of the concentrations of Pi and F-1-P found after fructose injection. The activity of the enzyme was reduced 88% by these additions (from 5.9 to 0.74 μ-moles/g min, p 0.001). Therefore, it appears that in vivo the activity of liver phophorylase is reduced by two mechanisms, a conversion of the active to the inactive form, and an inhibition of the remaining active enzyme by the elevated F-1-P and reduced Pi levels.