Myo-inositol and prostaglandins reverse the glucose inhibition of neural tube fusion in cultured mouse embryos.

Neural tube defects in infants of diabetic mothers constitute an important and frequent cause of neonatal mortality/morbidity and long-term chronic handicaps. The mechanism by which normal neural tube fusion occurs is not known. The failure of rostral neural tube fusion seen in mouse embryos incubated in the presence of excess-D-glucose can be significantly prevented by the supplementation of myo-inositol to the culture medium. This protective effect of myo-inositol is reversed by indomethacin, an inhibitor of arachidonic acid metabolism leading to prostaglandin synthesis. Prostaglandin E2 added to the culture medium completely protects against the glucose-induced neural tube defect. These data suggest that the failure of neural tube fusion seen in diabetic embryopathy is mediated through a mechanism involving abnormalities in both the myo-inositol and arachidonic acid pathways, resulting in a functional deficiency of prostaglandins at a critical time of neural tube fusion.

Serum myoinositol concentrations in premature infants fed human milk, formula for infants, and parenteral nutrition.

Myoinositol concentration was studied in serum of 65 neonates and their mothers at the time of birth, in samples of various types of feedings for infants, and in serial serum samples of 15 premature infants receiving human milk, formulas for infants, or parenteral nutrition over a 3-wk period. At birth the serum concentration of myoinositol was greater in neonates than in their mothers (108 +/- 10 vs 52 +/- 6 mumol/L, respectively, means +/- SEM, p less than 0.01). In feedings for infants, the concentrations of myoinositol were significantly greater in human milk than in formulas or parenteral nutrition solutions (1840 +/- 451 vs 420 +/- 110 vs 100 +/- 8 mumol/L, respectively, p less than 0.001). Over a 3-wk period the serum concentration of myoinositol increased in infants receiving human milk but not in those receiving formulas or parenteral nutrition. Serum concentrations of myoinositol in neonates are greater than in adults and are directly influenced by myoinositol intake.

Hyperfiltration and renal disease in glycogen storage disease, type I.

A prospective study of 14 patients (ages 6 months to 33 years) with glycogen storage disease, Type I (GSD-I) was carried out in order to define the character and frequency of renal dysfunction. A marked increase in the glomerular filtration rate (GFR) was documented in virtually all subjects, with the mean GFR raised by approximately 50%, to the range of 170 ml/min/1.73 m2. While this constituted the only renal abnormality found in the younger patients, a significant increase in urinary albumin excretion was seen in three teen-aged individuals; three patients over 20 years of age exhibited frank proteinuria (2 to 8 g/day). Renal biopsy on two of the proteinuric subjects revealed focal and global glomerulosclerosis and interstitial fibrosis. Evaluation of factors known to cause an increase in GFR did not define the precise etiology for its elevation in GSD-I. These studies suggest that: (1) glomerular damage and chronic renal disease are common in older patients with GSD-I; (2) the renal injury appears to be specifically related to GSD-I and is not secondary to the treatment of the disease; and (3) the natural history of the renal lesion in GSD-I may be analogous to that seen in insulin-dependent diabetes, with a "silent" period where hyperfiltration is the only demonstrable renal abnormality, followed by evidence of increasing glomerular damage progressing from microalbuminuria to frank proteinuria.

Effect of dichloroacetate on the exercise performance of patients with heart failure.

The reduced maximal exercise capacity of patients with heart failure has been attributed to skeletal muscle underperfusion with resultant intramuscular lactic acidosis and muscular fatigue. To investigate this hypothesis, the effect of dichloroacetate, a drug that decreases lactate formation by increasing pyruvate oxidation, on the maximal exercise performance of 18 patients with heart failure and reduced ejection fraction (25 +/- 9%) was examined. Exercise tests after parenteral dextrose (control) and dichloroacetate were performed 1 week apart. The sequence of interventions was randomized in a double-blind manner. Dichloroacetate decreased blood lactate at rest (control 8.0 +/- 2.5 versus dichloroacetate 5.6 +/- 2.9 mg/dl), throughout exercise and at peak exercise (control 26.0 +/- 14.3 versus dichloroacetate 19.4 +/- 10.8) (all p less than 0.05). In contrast, dichloroacetate had no effect on exercise time (control 15.2 +/- 6.0 versus dichloroacetate 15.9 +/- 6.2 min) or peak exercise oxygen consumption (control 1,280 +/- 498 ml/min versus dichloroacetate 1,312 +/- 530 ml/min) (both p = NS). In six subjects, dichloroacetate also had no effect at peak exercise on leg blood flow (control 2.8 +/- 1.1 versus dichloroacetate 3.0 +/- 0.6 liters/min) or femoral oxygen vein saturation (control 12.7 +/- 4.1% versus dichloroacetate 12.5 +/- 5.7%). These data suggest that intramuscular lactate accumulation is not responsible for muscular fatigue during exercise in patients with heart failure.

Effect of dichloroacetate in the treatment of anoxic lactic acidosis in dogs.

Lactic acidosis is seen frequently after severe anoxia and circulatory failure. Because dichloroacetate (DCA) has been shown to be effective in the treatment of lactic acidosis, we studied its effect on lactate levels and pH in arterial and sagittal sinus blood specimens in a pediatric canine model of anoxic cardiac arrest followed by CPR. Lactate levels rose steadily in all puppies receiving DCA alone (group 1), DCA plus bicarbonate (group 2), bicarbonate alone (group 3), or neither drug (group 4). Arterial and sagittal-sinus lactate levels were in the range of 2 mmol/L during the baseline period, 6 mmol/L after anoxic arrest, and 10 mmol/L after 20 min of CPR. Bicarbonate, but not DCA, significantly raised arterial pH. Neither drug reversed the progression of acidosis in the sagittal sinus; mean pH ranged from 6.85 to 6.92 among the four groups after 20 min of CPR. We speculate that DCA did not decrease lactate levels or raise the pH in either the peripheral circulation or the CNS (sagittal sinus) because of poor perfusion achieved during closed-chest cardiac compression.

Mechanism of skeletal muscle underperfusion in a dog model of low-output heart failure.

To investigate the mechanism responsible for underperfusion of working skeletal muscle in heart failure, we measured systemic and femoral bed hemodynamics during treadmill exercise and gracilis muscle resistance during contraction frequencies of 1-9 Hz in 8 dogs ventricularly paced at 260 beats/min for 3 wk to induce heart failure (HF) and in 9 control dogs. At peak treadmill exercise (4 mph, 10%), HF dogs had reduced cardiac outputs (control: 297 +/- 42 vs. HF: 212 +/- 16 ml X min-1 X kg-1) and femoral bed flows (control: 352 +/- 112 vs. HF: 229 +/- 95 ml/min) and elevated arterial lactates [control: 1.7 +/- 0.7 vs. HF: 4.1 +/- 0.7 mM (all P less than 0.04)], consistent with skeletal muscle underperfusion. This muscle underperfusion was associated with reduced mean arteriovenous pressure gradients [control: 119 +/- 12 vs. HF: 91 +/- 9 mmHg (P less than 0.001)] but with normal systemic vascular [control: 21 +/- 6 vs. HF: 23 +/- 5 U (P = NS)] and femoral bed resistances [control: 3.5 +/- 1.6 vs. HF: 4.4 +/- 2.3 X 10(2) U (P = NS)]. Both groups also had similar gracilis muscle minimal resistance during exercise (control: 2.0 +/- 1.1 vs. HF: 1.9 +/- 0.9 X 10(3) U/100 g) and following maximal vasodilation (control: 2.0 +/- 1.0 vs. HF: 2.1 +/- 1.0 X 10(3) U/100 g). These results suggest that 1) short-term rapid ventricular pacing in the dog produces a model of low output HF resembling HF in humans, and 2) skeletal muscle underperfusion in this model is due to a reduced muscle arteriovenous pressure gradient and not to impaired skeletal muscle arteriolar vasodilation.

Hyperglycemia-induced teratogenesis is mediated by a functional deficiency of arachidonic acid.

Congenital malformations now represent the largest single cause of mortality in the infant of the diabetic mother. The mechanism by which diabetes exerts its teratogenic effects is not known. This study evaluated whether arachidonic acid might be involved, a possibility raised by the role of arachidonic acid in palatal elevation and fusion, processes analogous to neural tube folding and fusion. This hypothesis was tested in two animal models of diabetic embryopathy, the in vivo pregnant diabetic rat and the in vitro hyperglycemic mouse embryo culture. The subcutaneous injection of arachidonic acid (200-400 mg/kg per day) into pregnant diabetic rats during the period of organ differentiation (days 6-12) did not alter the maternal glucose concentration, the maternal weight gain, or the weight of the embryos. However, the incidence of neural tube fusion defects was reduced from 11% to 3.8% (P less than 0.005), the frequency of cleft palate was reduced from 11% to 4% (P less than 0.005), and the incidence of micrognathia was reduced from 7% to 0.8% (P less than 0.001). The addition of arachidonic acid to B10.A mouse embryos in culture also resulted in a reversal of hyperglycemia-induced teratogenesis. The teratogenic effect of D-glucose (8 mg/ml) in the medium resulted in normal neural tube fusion in only 32% of the embryos (P less than 0.006 when compared to controls). Arachidonic acid supplementation (1 or 10 micrograms/ml) produced a rate of neural tube fusion (67%) that was not significantly different from that observed in controls. The evidence presented indicates that arachidonic acid supplementation exerts a significant protective effect against the teratogenic action of hyperglycemia in both in vivo (rat) and in vitro (mouse) animal models. These data therefore suggest that the mechanism mediating the teratogenic effect of an increased glucose concentration involves a functional deficiency of arachidonic acid at a critical stage of organogenesis.

The effect of 15-hour fat infusions of varying dosage on bilirubin binding to albumin.

Intravenous fat emulsions (1, 2, and 3 g/kg) were administered over 15 hr to 20 appropriate for gestational age premature infants with physiologic hyperbilirubinemia to determine the effect of fat infusions on the serum free fatty acid:albumin molar ratio (F/A) and on unbound bilirubin. Significant increases (p less than 0.05) in F/A occurred with each increase in lipid dose in infants less than 30 wk gestation, but not in infants greater than or equal to 30 wk gestation. There was a direct linear correlation (r = 0.65, p less than 0.001) between F/A ratio and unbound bilirubin (estimated fluorometrically by the ratio of albumin-bound bilirubin/reserve bilirubin binding capacity, B/R). The largest increases in unbound bilirubin (albumin-bound bilirubin/reserve bilirubin binding capacity) were seen in infants with F/A greater than 4.0. The gestational age of infants with F/A greater than 4.0 was significantly less (p less than 0.01) than infants with F/A less than 4.0 (28.7 +/- 0.47 vs. 31.1 +/- 0.40 wk, mean +/- SEM). In 10/58 infusions there was a fall in unbound bilirubin, unrelated to birthweight, gestational age, postnatal age, however, during these infusions the end-infusion F/A was greater than or equal to 3.0. We conclude that 1 g/kg of lipid emulsion infused over a 15-hr period has minimal risk of decreasing bilirubin binding in premature infants less than 30 wk gestation. As doses of 2 or 3 g/kg are used, these infants may be at risk of decreased bilirubin binding, due to elevations in the F/A ratio. Monitoring of the F/A ratio may identify infants at risk for decreased bilirubin binding during lipid infusion and provide guidelines for determining the appropriate lipid dose.

Metabolic and mitochondrial morphological changes that mimic Reye syndrome after endotoxin administration to rats.

The administration of sublethal doses of Escherichia coli O111:B4 endotoxin to starved rats results in significant increases in plasma ammonia, free fatty acids, and serum lactate compared with starved controls. These metabolic alterations are associated with Reye syndrome-like histological findings of hepatic microvesicular fatty accumulation and hepatic ultrastructural evidence of mitochondrial pleomorphism with matrix disruption. This sublethal endotoxin model may help elucidate the relationship between the hepatic mitochondrial injury, characteristic metabolic impairment, and encephalopathy seen in patients with Reye syndrome.

Relationship between uphill running performance at altitude and blood metabolite levels.

Venous blood samples were obtained from 18 marathon runners before and after the 27 km uphill portion of a 46 km transmountain race at altitudes of 1,950-3,400 m. There was an inverse correlation between blood lactate levels and running time (r = -0.83), with the runners with higher lactate levels completing the race in less time. The faster half of the group had higher blood levels of glucose and lactate and lower free fatty acid levels at 26 km distance and 3,400 m elevation. The elevated lactate concentrations in the blood of the faster runners suggest that anaerobic metabolism can contribute significantly to total energy production during prolonged exercise at high altitude.

D-Lactic acidosis in children: an unusual metabolic complication of small bowel resection.

Acidosis caused by intestinal bacterial D-lactate production occurs in ruminants engorged with carbohydrate. A similar phenomenon was identified in two children who developed recurrent episodes of metabolic acidosis and peculiar neurologic symptoms in response to increased dietary carbohydrate after major small bowel resections. Both children were found to have elevated plasma concentrations of D-lactic acid at the time of each episode. Acid base and neurologic abnormalities responded immediately to neomycin therapy. Among a number of microorganisms isolated from stool cultures of these patients, one anaerobic Lactobacillus acidophilus species produced large amounts of D-lactate in vitro. Reduction in carbohydrate intake in one patient tested led to a fall in D-lactate generation. We believe that excessive D-lactate production by intestinal bacteria, from malabsorbed carbohydrate, may produce metabolic acidosis and neurologic symptoms in children with small bowel resections.