Measurement of the sodium membrane potential by NMR.

Using nuclear magnetic resonance (NMR), we have developed a method of noninvasively determining the transmembrane sodium potential in erythrocytes by measuring intracellular and extracellular sodium concentrations. The experimental values correlated well with values obtained from standard flame photometric methods.

1H nuclear magnetic resonance spectroscopy study of neonatal hypoglycemia.

It has been hypothesized that the mechanism of hypoglycemic brain damage involves energy failure or excessive accumulation of excitatory neurotransmitters. To test these hypotheses, 1H nuclear magnetic resonance spectroscopy was employed to determine brain high-energy phosphates, carbohydrates, neurotransmitters, amino acids, and fatty acids during insulin-induced hypoglycemia in the neonatal dog. Reduction in brain glucose content was associated with an increase in blood/brain lactate ratio, as well as decreases in brain glutamate, aspartate, taurine, and inositol; however, no change was observed in GABA concentration or in brain energy state. In contrast to the adult experimental animal, brain tissue injury due to hypoglycemia is minimal in the neonatal animal. The mechanism of resistance to hypoglycemic brain injury may involve modulation of the rise of excitatory amino acids and decline in inhibitory neurotransmitters and high-energy phosphates.

Pediatric genitourinary tumors.

Although genitourinary tumors make up only 10% of childhood cancers, with Wilms' tumor accounting for most, the study of these tumors has yielded a model of cancer development. Tremendous interinstitutional and international cooperation has improved the survival and lowered the morbidity of treatment. Advances in molecular biology and improvement in experimental techniques make this a tremendously exciting field, with discoveries being made almost routinely. Most importantly, however, the study of this group of tumors and the ensuing application of multi-modality therapy has saved the lives of thousands of children.

Oxybutynin decreases renal pelvic pressures in normal and infected rat urinary tract.

Since abnormally elevated renal pelvic pressures may contribute to renal damage, we examined whether an anticholinergic agent could decrease elevated renal pelvic pressures. We have previously demonstrated in a rat model that renal pelvic pressures rise physiologically during normal bladder filling and high urinary flows; these pressures rise to abnormal levels during acute urinary tract infection (UTI). In these studies we investigated the effects of oxybutynin on the in vivo rat urinary tract. Simultaneous bladder and renal pelvic pressures were measured with and without oxybutynin at low (<2 ml./kg./hr.), moderate (2-10), high (10-20), and very high (>20) urinary flows while the rat bladder filled and emptied spontaneously. Although minimal differences were found between bladder filling pressures with and without oxybutynin, at higher urinary flows the renal pelvic pressure in oxybutynin treated rats was significantly lower than in nontreated animals. Indeed, when rats with urinary tract infection were treated with oxybutynin, their renal pelvic pressures were lower than those in uninfected rats. We conclude that oxybutynin affects rat upper urinary collecting system pressures, and is capable of decreasing abnormally elevated renal pelvic pressures due to urinary tract infection to normal or subnormal levels.

The effect of hypotension on brain energy state during prolonged neonatal seizure.

Prolonged seizures in the human neonate may be complicated by systemic hypotension. To examine the effect of systemic hypotension on brain metabolic state during seizure, neonatal dogs were made hypotensive (by exsanguination) during bicuculline-induced seizure. Measurement of regional cerebral blood flow showed that moderate hypotension did not impair cerebral perfusion during seizure. Measurement of brain energy state with in vivo 31P nuclear magnetic resonance spectroscopy disclosed a similar pattern of alteration of high energy phosphates in animals subjected to seizure or to the combination of seizure and hypotension. The additional metabolic stress imposed by moderate hypotension during seizure in the neonatal dog appears to be slight.

The effect of tin protoporphyrin on the bilirubin production rate in newborn rats.

Using a flow-through system, the pulmonary excretion rate of carbon monoxide (VECO) was determined by gas chromatography and used as an index of bilirubin production in newborn rats treated with tin protoporphyrin. Hepatic and splenic heme oxygenase activities were determined spectrophotometrically. No significant differences in the VECO were found between experimental and control animals despite significant decreases in hepatic heme oxygenase activity (P less than .0005) and splenic heme oxygenase activity (P less than .025). These results suggest that 1) there is no simple relation between heme oxygenase activity and bilirubin production; 2) heme oxygenase is present in excess amounts in neonatal rats; and 3) the lowering of serum bilirubin levels caused by tin protoporphyrin cannot be attributed to decreased bilirubin production and may be owing instead to increased uptake, conjugation, or excretion of bilirubin, or decreased enterohepatic circulation of bilirubin.

In vivo 31P and in vitro 1H nuclear magnetic resonance study of hypoglycemia during neonatal seizure.

To examine the hypothesis that hypoglycemia has an adverse effect on brain energy state during seizure, neonatal dogs were subjected to bicuculline-induced seizure while hyperglycemic, normoglycemic, or hypoglycemic. Cerebral blood flow increased and remained elevated in all animals subjected to seizure, regardless of blood or brain glucose concentration. In vivo 31P nuclear magnetic resonance spectroscopy disclosed a small (10-20%) decrease in adenosine triphosphate levels and a greater (20-40%) decline in phosphocreatine levels in animals experiencing seizure, irrespective of whether they were hyper-, normo-, or hypoglycemic. In vitro analysis of brain extracts with 1H nuclear magnetic resonance spectroscopy disclosed a significant elevation of lactate in all seizing animals. There were differences in brain alanine, glycine, and beta-hydroxybutyrate levels between the hyperglycemia-seizure and hypoglycemia-seizure groups. Alternate substrates such as lactate, fatty acids, or amino acids may be used when neonatal seizure is complicated by hypoglycemia, thereby preventing further deterioration of brain metabolic state.

Pulmonary excretion rates of carbon monoxide using a modified technique: differences between premature and full-term infants.

The pathophysiology of the exaggerated hyperbilirubinemia in premature infants remains unclear. The relative contribution of bilirubin production may be estimated by measuring the pulmonary excretion rate of carbon monoxide (VeCO). We found that the mean VeCO of premature infants, 16.7 +/- 5.0 microliters/kg/h, was significantly elevated (p less than 0.05) compared with the mean VeCO of full-term infants, 13.9 +/- 3.5 microliters/kg/h. Premature infants who required phototherapy had a significantly (p less than 0.05) higher mean VeCO than those who did not. The VeCO did not correlate with gestational age, implying that factors which associate frequently but variably with gestational age may have an important influence on heme catabolism.

Paired determinations of blood carboxyhemoglobin concentration and carbon monoxide excretion rate in term and preterm infants.

Paired determinations of COHb and VeCO were performed on 30 term infants (38 to 42 weeks' gestation) and 26 preterm infants (28 to 37 weeks' gestation) during the first week of life. All subjects were breathing room air at the time of the study. Values of COHb were corrected for RAco by linear regression of COHb (percent saturation) vs RAco (ppm). Regression coefficients for term and preterm infants with no history of pulmonary impairment were nearly identical (COHb = 0.175 RAco + 0.45, r = 0.77, n = 25 for term infants; COHb = 0.168 RAco + 0.51, r = 0.82, n = 9 for preterm infants) and agreed well with theoretical values. For the group of term infants, linear regression of Veco (microliter/kg/hr) vs. COHbc, where COHbc = COHb - 0.17 RAco, resulted in VEco = 23.4 COHbc + 4.02, r = 0.75, n = 30. The corresponding relationship for preterm infants with no history of pulmonary impairment was VEco = 24.7 COHbc + 3.85, r = 0.61, n = 13. For a subpopulation of preterm infants with a history of pulmonary dysfunction, the correlation decreased significantly, with VEco = 4.34 COHbc + 17.6, r = 0.097, n = 11. These results demonstrate that (1) COHbc is a reasonable index of VEco and consequently of the heme catabolic rate in both term and preterm infants with no clinical history of pulmonary dysfunction and (2) inference of VEco from COHbc may be misleading in certain cases without a consideration of the factors relating these two variables.

Effect of tin protoporphyrin on the excretion rate of carbon monoxide in newborn rats after hematoma formation.

This study evaluated the efficacy of tin protoporphyrin (TP), a competitive inhibitor of heme oxygenase, in suppressing the total body excretion rate of carbon monoxide (CO), an index of total bilirubin formation, in neonatal rats with artificially created hematomas. Wistar rat litters less than 12 h old were each divided into three groups of similar weight and treated as follows: (a) saline control (S); (b) hematoma, 80 microliter blood (H); (c) TP, 65 mumol/kg, and hematoma (TP-H). CO excretion of the H group increased rapidly after hematoma formation, reaching a maximum value of 79 +/- 4 SE microliter/kg/h 25 h later. Treatment with TP did not affect the pattern of CO excretion or its magnitude (78 +/- 2 SE microliter/kg/h, 25 h posthematoma). The S group showed no increase in CO excretion at this time (40 +/- 2 SE microliter/kg/h). At the conclusion of the experiment (45 h posthematoma), the plasma total bilirubin levels were slightly lower in the TP-H rats (1.0 +/- 0.1 SE mg/dl) than in H rats (1.2 +/- 0.1 SE mg/dl). The S rats had a plasma total bilirubin concentration of 0.8 +/- 0.1 SE mg/dl. The hepatic and splenic heme oxygenase activities were decreased by 61% (p less than 0.001) and 48% (p less than 0.05), respectively, in the TP-H rats as compared to the H rats. The S and H rats had similar enzyme activities. The results of this study suggest that though single-dose TP decreased tissue heme oxygenase activity, it did not significantly affect total bilirubin formation.

The effect of diazepam on neonatal seizure: in vivo 31P and 1H NMR study.

It is assumed that when anticonvulsants arrest seizure, there is rapid return of brain high energy phosphates and brain lactate to control values. To test this hypothesis, diazepam was administered to neonatal dogs during flurothyl-induced seizure. In vivo 31P nuclear magnetic resonance spectroscopy disclosed that diazepam quickly arrested electrographic seizure and restored brain phosphocreatine and inorganic phosphate to baseline values. In contrast, in vivo 1H nuclear magnetic resonance spectroscopic measurements showed that arrest of seizure with diazepam did not return brain lactate to control values. The sustained increase in cerebral blood flow and prolonged elevation of brain lactate, acetate, valine, and succinate in the postictal period indicate that metabolic recovery of the brain occurs over an extended period of time after the normalization of EEG, phosphocreatine, and brain pH.

Pulmonary excretion rate of carbon monoxide as an index of total bilirubin formation in adult male Wistar rats with common bile duct ligation.

Total bilirubin formation (TBF) in the rat after a short period of common bile duct ligation was studied by measuring the pulmonary excretion rate of CO (VECO). At postoperative day 3, the VECO of experimental animals was higher when compared with the preoperative VECO (p less than 0.005); whereas the VECO of control animals did not change. Also, on the 3rd postoperative day, the relative rate of early labeling of bilirubin following the administration of delta-aminolevulinic acid-5-14C, a preferential hepatic heme synthesis precursor, was similar between the experimental and control animals; only the experimental animals had an abnormal peroxide hemolysis test. We conclude that common bile duct ligation in the rat is associated with elevations in the VECO, indicating significant increases in TBF, and the source of the increase is probably of erythropoietic origin. This finding may be relevant to the understanding of the pathophysiology of obstructive jaundice in human neonates.