Jan M. Goplerud

Decreased erythrocyte Na+, K+-ATPase activity associated with cellular potassium loss in extremely low birth weight infants with nonoliguric hyperkalemia

To determine whether a shift of potassium ions from the intracellular space to the extracellular space accounts, in part, for the hyperkalemia seen in extremely low birth weight infants, we examined potassium concentration in serum and erythrocytes from extremely low birth weight infants with hyperkalemia (n = 12) or with normokalemia (n = 27). In addition, to determine whether the shift of potassium was associated with low sodium-potassium-adenosinetriphosphatase (Na+,K(+)-ATPase) activity, we studied the activity of ATPase in the last 16 infants enrolled in the study. Fluid intake and output were measured during the first 3 days of life. Infants were considered to have hyperkalemia if the serum potassium concentration was 6.8 mmol/L or greater. Blood was obtained daily for intracellular sodium and potassium levels by means of lysis of erythrocytes. The remaining erythrocyte membranes were frozen and analyzed for Na+,K(+)-ATPase activity. There were significantly lower intracellular potassium/serum potassium ratios in the infants with hyperkalemia for each day of the 3-day study (p < 0.001). In the hyperkalemic group, there was lower Na+,K(+)-ATPase activity than in the infants with normokalemia (p = 0.006). Low Na+,K(+)-ATPase activity was associated with lower intracellular potassium/serum potassium ratios (p = 0.006), higher serum potassium values (p = 0.02), and lower intracellular potassium concentration (p = 0.009). The urinary data demonstrated that there was no difference in glomerulotubular balance between the two groups. We conclude that nonoliguric hyperkalemia in extremely low birth weight infants may be due, in part, to a shift of potassium from the intracellular space to the extracellular space associated with a decrease in Na+,K(+)-ATPase activity.

Effect of nordihydroguaiaretic acid on cerebral blood flow and metabolism during hypoxia in Newborn piglets

Nordihydroguaiaretic acid (NDGA), a lipoxygenase inhibitor, was investigated for its effect on cerebral blood flow (CBF) and cortical oxygen consumption during hypoxia in 9 anesthetized, ventilated newborn piglets. CBF was measured by radioactive microspheres while brain cortical metabolism was evaluated by continuous 31P-NMR spectroscopy. Five piglets were treated with NDGA (3 mg/kg i.v. in 50% ethanol as vehicle) prior to hypoxia and had CBF measured before NDGA (control), 15 min after NDGA (baseline) and then after 15 and 45 min of hypoxia following NDGA. Another 4 piglets were treated with vehicle (2 ml/kg 50% ethanol) under the same protocol. In the NDGA-treated piglets, cerebral cortical O2 consumption for a given PCr/Pi was significantly increased (p < 0.05) compared to non-NDGA. Since NDGA inhibits production of vasoconstricting leukotrienes during hypoxia, cortical capillary beds otherwise constricted may be perfused following NDGA, thus increasing the O2-consuming tissue area.

Cerebral Blood Flow and Metabolism during Repeated Asphyxias in Newborn Piglets: Influence of Theophylline

The effect of theophylline on cerebral blood flow (CBF), oxygen transport, and energy metabolism was investigated during and following brief episodes of asphyxia. CBF was determined by microspheres during control, asphyxia, and recovery with reventilation after a single asphyxia (recovery I) and after 7 repeated asphyxias (recovery II). In addition, cerebral energy metabolism by 31P NMR spectroscopy and cerebral oxygen consumption (CMRO2) in newborn piglets treated with 30 mg/kg theophylline (serum levels 22-25 micrograms/ml) were compared with nontreated piglets. Theophylline increased CMRO2 during recovery I (348 mumol O2/min/100 g vs. 144 for non-theophylline) but not during control, asphyxia, or recovery II. There was no significant difference between the theophylline and non-theophylline groups in depletion of phosphoenergetics as measured by 31P NMR.

The Effect of Reoxygenation with 21% and 100% Oxygen Following Hypercapnic Hypoxia on the Glutamate Site of the NMDA Receptor in the Brains of Newborn Piglets. |[dagger]| 904

The Effect of Reoxygenation with 21% and 100% Oxygen Following Hypercapnic Hypoxia on the Glutamate Site of the NMDA Receptor in the Brains of Newborn Piglets. † 904

DIFFERENCES IN CEREBRAL CORTICAL VS. STRIATAL Na + ,K + -ATPase RESPONSE TO REPEATED ASPHYXIAS AND REVENTILATION WITH EITHER 21% OR 100% OXYGEN IN NEWBORN PIGLETS. † 2232

DIFFERENCES IN CEREBRAL CORTICAL VS. STRIATAL Na + ,K + -ATPase RESPONSE TO REPEATED ASPHYXIAS AND REVENTILATION WITH EITHER 21% OR 100% OXYGEN IN NEWBORN PIGLETS. † 2232

79 EFFECT OF REPEATED ASPHYXIA/REVENTRATION ON STRIATAL DOPAMINE RELEASE AND CEREBRAL CORTICAL OXYGEN PRESSURE IN NEWBOFN PIGLETS

The striatum, richly innervated by the nigrostriatal dopaminergic pathway, is a brain region highly vulnerable to ischemic/hypoxic neuronal damage and especially affected by repetitive insults. The present study tests the hypothesis that recurrent asphyxia/reventilation alters extracellular dopamine (DA) by decreasing cerebral cortical oxygenation in the striatum of newborn piglets. Anesthetized, ventilated piglets (n=7) underwent seven repeated episoces of 3 min asphyxia, each followed by 15 min reventilation/recovery. Cortical O2 pressure, phosphorescence quenching, and extracellular striatal DA. by in vivo microdialysis, were measured continuously. Serum lactate levels increased from 4±3 mM/L (baseline) to 16±1 mM/L after the 7th episode of asphyxia/ reventilation. Cortical O2 pressure decreased from 39±9 Torr (baseline) to 11±6 Torr during each asphyxia then rapidly returned to baselne values, except after the 7th asphyxia when it returned to baseline in 10 min then decreased again to 19±4 Torr. Extracellular DA concentration was dependent on the number of asphyxia episodes and was higher after each successive asphyxia. From the 2nd to 7th asphyxia, extracellular DA increased from baseline of 6.5 to 9, 12.6. 26, 57, and 84 pmoles/ml, respectively. During 15 min reventilation. DA returned to baseline levels for the first 5 asphyxias, but after the 6th and 7th episodes, DA remained higher than baseline by 50-70%. This progressive DA accumulation could result from hypoxia-induced DA release or from impaired DA reuptake and/or degradation. Thus, repeated episodes of asphyxia were associated with progressive disturbance of striatal DA metabolism, leading to high levels af extracellular DA which represent a potential mechanism of post-asphyxial striatal neuronal injury. Funded by NIH #HD-20337.

ALLOPURINOL MAY ALTER INTRACEIXULAR CEREBRAL METABOLISM DURING HYPOXIA IN NEWBORN PIGLETS

Allopurinol is a xanthine oxidase inhibitor and free radical scavenger potentially protective in hypoxic tissue injury. The present studies compare 5 allopurinol-treated, anesthetized, mechanically ventilated newborn piglets to 5 non-treated piglets during normoxia and after 25 min (HYP 1) and 50 min (HYP 2) of hypoxia by ↓FiO2. The allopurinol group received 5 mg/kg IV 30 min prior to hypoxia. Cerebral cortical O2 delivery and O2 consumption were calculated using microsphere determined blood flows. To assess brain cortical oxygenation, phosphocreatine to inorganic phosphate ratio (PCr/Pi) and intracellular pH (pHi) were determined concurrently by 31-P NMR spectroscopy. Sagittal sinus lactate levels and arterial blood gases were also measured. Brain O2 delivery, O2 consumption, and PCr/Pi were the same for the allopurinol treated and non-treated groups during normoxia, HYP 1, and HYP 2. However, arterial pH was significantly lower in the allopurinol treated vs non-treated piglets during both HYP 1 (7.16±0.06 vs 7.30±0.04) and HYP 2 (6.93±0.14 vs 7.11±0.10) despite comparable PCO2 (36 ± 8 vs 39±8), PO2 (24±2 vs 26±6), and baseline pH (7.40±0.10 vs 7.40±0.03). Similarly, cerebral cortical pHi was lower in the allopurinol treated piglets during hypoxia: HYP 1 (6.77±0.21 vs 6.93±0.39) and HYP 2 (6.43±0.22 vs 6.71±0.39) and the increase in sagittal sinus lactate levels during hypoxia was greater for the allopurinol vs non-treated piglets: HYP 1 (9.5±2.5 vs 5.4±2.5) and HYP 2 (14±3.4 vs 6.71 ± 5.7). The data suggest an alteration in the metabolic response to hypoxia of the allopurinol treated group. If allopurinol interferes with hypoxia-induced cerebral cellular adaptation, accelerating brain tissue lactic acidosis, it may contribute to hypoxic tissue damage despite reducing free radical injury by other mechanisms. (NIH #20337).

1397 HEMODYNAMIC RESPONSE TO SINGLE AND REPEATED EPISODES OF APNEA IN NEWBORN (NB) PIGLETS

This study investigates the ability of hemodynamic mechanisms to respond to multiple episodes of apnea in 5 NB piglets. Following catheterization and tracheostomy, piglets were paralyzed and mechanically ventilated (PO2 = 60-70 torr, pH = 735-7.45, PCO2 = 30-35). After baseline measurements of blood gases, pH, Hct. BP, HR, and organ blood flow by microspheres, apnea to the point of bracycardia (HR < 80) was induced by disconnecting the ventilator; 30-40 sec later, mechanical ventilation was resumed until HR and BP returned to baseline. A total of 7 apneas were induced over 1½ hrs. Microspheres were injected during the first apnea (PO2 = 16±13, pH = 7.34±.06, PCO2 = 42±5), recovery from first apnea (Rec 1), and ½ hr after the 7th apnea (Rec 2). Tissue blood flows (ml/min/100g, mean ±S.E. and % change):The rapidity of hemodynamic response to apnea, redistribution of blood flow occurring 130-180 sec after cessation of ventilation, 30-40 sec after onset of bradycardia indicates oxygen sensitivity of newborn vasculature. Kidney and skeletal muscle flows return to near baseline during Rec 1 and Rec 2, while heart and brain flows remain elevated; lack of significant difference between Rec 1 and Rec 2 despite 6 intervening apneas suggests no cumulative effect in the newborn piglet of brief, repeated hypoxemic insults.

1374 CARBON MONOXIDE EFFECT ON BRAIN OXIDATIVE METABOLISM IN NEWBORN PIGLETS

The effect of carbon monoxide on brain oxidative metabolism was studied in 5 anesthetized newborn piglets during mechanical ventilation, at normoxic and normocarbic steady-state. Surface coil 31-Phosphorus (31-P) spectra (ATP, phosphocreatine (PCr), inorganic phosphoate (Pi), phosphomonoesters, and phosphodiesters), measured by NMR, were obtained every 4 min over a period of 2 hrs with a gradual increase of blood carboxyhemoglobin [COHb]. Measurements of blood gases, acidbase, and regional CBF were obtained at baseline, 30-40%, 50-60%, and 70-80% of blood [COHb] level, respectively. PCr/Pi decreased in all piglets from a mean of 1.65 to 0.5 in a linear relationship as a function of the gradual increase in [COHb] from 6.3 to 80.3%. CBF increased from 78 ml/min/lOOg to 172 to 220 parallel to increasing levels of [COHb] in all piglets. Oxygen delivery remained relatively unchanged from 466 umol/min/lOOg to 416 to 391, and decreased at [COHb] of 70-80% to 287 umol/min/100g. In contrast to previous data in our laboratory where PCr/Pi abruptly decreased when oxygen content reached 4%, PCr/Pi in the present studies remained relatively high for comparable decreased O2 content due to hypercarboxyhemoglobinemia, because blood flow remained relatively high in the presence of decreased oxygen content, whereas in hypoxic hypoxia flow was decreased at extreme hypoxemia. These data suggest that cerebral perfusion is better maintained in carbon monoxide than hypoxic hypoxia, possibly reflecting altered responsivity of brain vessels or adrenergic mechanisms capable of altering CBF as seen in hypoxic hypoxia.

1396 REGIONAL CEREBRAL BLOOD FLOW (CBF) RESPONSE TO APNEA IN NEWBORN (NB) PIGLETS

Previous studies have shown that sustained steady-state hypoxemia results in increased CBF with greatest increases to brainstem and subcortical structures. The present study investigates acute regional CBF response to single and repeated short (130 - 180 sec) apneas in 5 NB piglets. After catheterization and tracheostomy, piglets were paralyzed and mechanically ventilated (PO2=60-70, pH=7.35-7.45, PCO2=30-35) with 30% N2O. Following baseline measurements of blood gases, pH, Hct, BP, HR, and CBF by microspheres, apnea to the point of bradycardia (HR<80) was induced by disconnecting the ventilator, and repeated for a total of 7 apneas. CBF was measured during the first apnea (PO2=16 ± 13 torr, pH = 7.34 ± .06, PCO2 = 42 ± 5), recovery from first apnea (Rec 1), and ½ hr after the 7th apnea (Rec 2). During apnea, rapid regional CBF redistribution occurs, with decreased flow to the cerebrum 56 ± 4 ml/min/100g to 43 ± 7, -23%, caudate 76 ± 14 to 73±22, -10%, and choroid plexus 148 ± 25 to 86 ± 22, -<t3%, although total brain flow increased 66 ± 8 to 84 ± 15, +28%. Flow increased significantly (70 - 200%) to brainstem structures (midbrain 64 ± 6 to 108 ± 17, pons 90 ± 26 to 183 ± 61, medulla 59 ± 4 to 174 ± 28) with moderate increases (28 - 40%) to subcortical structures (thalamus 64 ± 7 to 88 ± 11, hippocampus 38 ± 4 to 51 ± 11, cerebellum 52 ± 3 to 67 ± 8). During Rec 1 and Rec 2, CBF remained elevated from baseline, 58% and 37%, respectively; the regional flow returned, however, to a more uniform distribution pattern. The nonhomogeneous regional CBF during apnea suggests differences in regional metabolism, response time, or vascular sensitivity to hypoxemia in the newborn brain.