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D D Gilboe

Publications and source records attributed to D D Gilboe.

At least 37 records · Page 2Linked to original sources
PubMed1983

Effect of blood pH and ischemia on kinetic constants for cerebral glucose transport.

In 117 experiments, the isolated canine brain was subjected either to 4-min pulses with blood ranging from pH 6.8 to 7.8, 30 min of hypoxia (PaO2 30 mmHg or 40 mmHg), or 30 min of complete ischemia followed by 60 min of perfusion with normal oxygenated blood. Unidirectional and net glucose fluxes were measured under all experimental conditions, and kinetic constants were calculated for unidirectional transport at each pH and after ischemia. In brains perfused with blood having a PaO2 of 30 or 40 mmHg, we observed a 58 and a 55% increase, respectively, in the net flux; however, there was no significant change in the unidirectional flux either during hypoxia or during the recovery period. Exposure of the brains to blood with a pH of 6.8, 7.0, and 7.2 had no effect on the unidirectional flux; however, as pH was raised above 7.4 both the Km and Vmax increased, reaching a maximum of 12.06 +/- 2.34 mM and 2.38 +/- 0.28 mumol X g-1 X min-1, respectively, at pH 7.8. The V/K ratio was unchanged. After 30 min of ischemia, there was a significant change (P less than 0.05) in the Km of the unidirectional glucose transport process from a control value of 5.84 +/- 1.75 mM to 17.40 +/- 5.50. These studies suggest that unidirectional flux is impaired after ischemia due to a decrease in the carrier's affinity for glucose; however, the observed changes are apparently unrelated to a fall in tissue pH. A similar mechanism is believed to be responsible for the decrease in unidirectional glucose flux after hypoxia.

Animals↗
PubMed1982

Effects of nitrous oxide on the cerebrovascular tone, oxygen metabolism, and electroencephalogram of the isolated perfused canine brain.

Nitrous oxide has been reported to act both as a stimulant and as a depressant of cerebral oxygen metabolism (CMRO2) and blood flow under a variety of experimental conditions in the intact animal. The isolated brain preparation is advantageous because it permits direct measurement of blood flow and allows the study of drug effects without interference from other organ systems or drugs. In this study, six isolated perfused canine brain preparations were used to compare the CMRO2, cerebral vascular resistance (CVR), and the EEG of brains perfused with normocapnic, normoxic blood equilibrated with either 70% N2O or 70% N2. There was no significant change in CMRO2. Cerebral vascular resistance fell [16.4% +/- 3.4% SEM (P less than 0.015)] during exposure to N2O. The EEG pattern was reduced in amplitude, but showed an increase in both low-voltage beta activity (14-40 Hz), and 3-5 Hz activity. In the isolated brain, N2O reduced cerebral vascular tone while exhibiting no effect on cerebral oxygen metabolism.

Animals↗
PubMed1982

Transport of glucose across the blood-brain barrier: reevaluation of the accelerative exchange diffusion.

In an earlier study of glucose transport across the blood-brain barrier it was concluded that the kinetic transport constants increase as the brain glucose concentration increases, a finding that was attributed to accelerative exchange diffusion (Betz et al. 1975). The conclusion, however, relied upon application of a commonly used simplified treatment of tracer extraction data. In this study it is demonstrated that the simplified treatment is applicable only in the case of zero brain glucose concentration, and a more general model for determination of the kinetic constants is developed. Re-analysis by this model of the data of Betz et al. (1975)--comprising a range of brain glucose concentrations--gave kinetic constants which did not vary significantly over a wide range of brain glucose concentrations. For brain glucose concentrations up to about 12 mmol 1(-1), the kinetic constants obtained for glucose transport across the blood-brain barrier are Km = 6.18 +/- 0.38 mmol 1(-1) Vmax = 1.65 +/- 0.06 mu mol g -1 min -1.

Animals↗
PubMed1982

Criteria of viability in isolated brain preparations.

Isolated brains were perfused for 30 min at 10, 20, 30 or 40 torr followed by up to 45 min of reoxygenation. Arterial and venous blood samples were drawn at frequent intervals before, during and after hypoxia for determination of oxygen and glucose content. Brain samples were frozen in situ before hypoxia, following 30 min of hypoxia and after 45 min of reoxygenation for measurement of adenine nucleotide and creatine phosphate (CrP) content. Neither the cerebral metabolic rate for oxygen (CMRO2) nor the ATP level returned to normal in the arterial pO2 10 and 20 torr groups. Although ATP reached normal levels in the arterial pO2 30 torr group following 45 min of reoxygenation. CMRO2 was 84% of normal and the CrP was only 63% of normal. However, ATP, CMRO2 and CrP were all normal in the arterial pO2 40 torr group following 45 min of reoxygenation. The failure of the arterial pO2 30 torr group to reach a normal CrP level is thought to be the result of a defect in brain energy metabolism whereby the cell was unable to generate ATP at a rate sufficient to restore CrP to normal levels. The defect appears to be signaled by a lower than normal CMRO2. The ability to effectively utilize oxygen to form ATP is believed to reside in the intact mitochondria of undamaged brain cells. Thus, the posthypoxic CMRO2 is an index of mitochondrial function and by implication it is a measure of the integrity of cerebral neurons.

Adenosine Triphosphate↗
PubMed1982

Increased blood oxygen affinity decreases canine brain oxygen consumption.

We have studied the effect of increased blood O2 affinity on O2 delivery to the isolated canine brain. After surgical isolation, the brain, enclosed in the calvarium, was perfused alternately from two pump-oxygenators with normal blood (P 50 [7.4] = 30 +/- 2 torr [S.D.]) and with blood whose P50 was reduced to 18 +/- 2 torr by carbamylation. [Hb], acid-base balance, blood gases, and flow rate were carefully matched in the two circuits. Although blood [Hb] was reduced to approximately 10 gm/dl, other perfusion variables such as CBF (65 +/- 6 ml/min/100 gm) and arterial blood oxygen saturation (96% to 99%) were normal for the dog. Under these conditions cerebral VO2 (Fick) averaged 3.87 +/- 0.73 ml/min/100 mg (S.D.) with control blood and 2.94 +/- 0.69 with low P50 blood (mean delta = 24%, n = 14, p less than 0.001), and PVO2 averaged 31 +/- 2 and 21 +/- 2 torr, respectively (p less than 0.001). The fall in VO2 during low P50 perfusion was associated with a decrease in [A-V]O2 difference and a rise in CVO2 of 1.2 ml/dl, which suggests that O2 extraction at PVO2 approximately 20 torr is curtailed. The EEG, previously shown to correlate with VO2 in this model, invariably deteriorated after 30 to 60 sec of low P50 perfusion and improved in 30 to 60 sec after reperfusion with normal blood. CBV increased by 0.9 ml/100 gm during low P50 perfusion, implying capillary recruitment. In a parallel series of experiments, four brains were alternately perfused with normal blood (pH 7.41, PCO2 38 torr, P50 [7.4] = 30 torr) and alkalotic blood (pH 7.98, PCO2 39 torr, P50 [7.98] = 17.3 torr). With flow rates equal for both normal and experimental blood, PVO2 averaged 31 +/- 4 (S.D.) and 21 +/- 3 torr (p less than 0.001), respectively, and VO2 averaged 4.33 +/- 0.52 ml/min/100 gm and 3.18 +/- 0.52 (p less than 0.001). With pH at 7.4 and 7.8, VO2 averaged 4.42 +/- 0.77 ml/min/100 gm and 3.66 +/- 0.99, respectively (p less than 0.01). The data indicate that a reduced P50 limits O2 diffusion to brain at a normal but fixed blood flow rate despite capillary recruitment.

Animals↗
PubMed1980

Brain metabolism after 30 minutes of hypoxic or anoxic perfusion or ischemia.

In 48 separate experiments, isolated canine brain preparations were subjected to 30 min of either hypoxic (PaO2 congruent to 20 mmHg) perfusion, anoxic (PaO2 < 10 mmHg) perfusion, or total ischemia followed by reperfusion for up to 2 h with normal oxygenated blood. Unlike ischemia and anoxia, energy metabolism was sufficient during hypoxia to maintain substantial levels of ATP (48% of normal), sustain normal ion gradients, and prevent edema formation. Posthypoxia metabolism was adequate to clear accumulated lactate, enable recovery of normal tissue glucose levels, and allow return to normal levels of glycolytic intermediates. Although not as complete as that following hypoxia, recovery from cerebral edema and restoration of metabolism were better in ischemic than anoxic cortex. The reduced oxygen uptake in all groups during reoxygenation (55% of normal) indicates that all have a diminished capacity for energy metabolism. The ATP levels recovered more rapidly after 15 min of reoxygenation in the anoxic (57% of normal) than in the ischemic (21% of normal) group. Thus ATP does not appear to be directly related to recovery from edema.

Adenosine Triphosphate↗
PubMed1977

Cytochalasin B inhibition of brain glucose transport and the influence of blood components on inhibitor concentration.

The effect of cytochalasin B on cerebral glucose transport and metabolism was investigated in 19 isolated perfused dog brain preparations. Cytochalasin B is a potent, non-competitive inhibitor of glucose transport at the blood-brain interface. Both glucose transport into (Ki = 6.6 +/- 1.9 micrometer) and out of the capillary endothelial cell are inhibited. The inhibition is readily reversible by perfusion with blood containing no cytochalasin B. After 2 min of exposure to 30 micrometer cytochalasin B, the cerebral oxygen consumption decreases by 31% probably due to decreased availability of glucose for oxidative metabolism. About one-half of the cytochalasin B that is dissolved in blood is bound to erythrocytes and other blood components while the remainder is free.

Animals↗
PubMed1977

Blood-brain amino acid transport and content during anoxia and reoxygenation.

The isolated dog brain preparation was used to investigate the dynamics of cerebral amino acid metabolism during perfusion with anoxic blood (PO2 less than 10 mmHg). Significant uptake of histidine and lysine, as determined by arteriovenous (A-V) differences in whole blood samples, was observed during 30 min of cerebral anoxia. The A-V differences determined from plasma samples indicated that uptake of histidine and efflux of glutamic acid and proline had occurred. Nitrogen balance in the preparation appeared to be maintained. Thirty minutes of anoxic perfusion resulted in increased tissue concentrations of five essential amino acids (methionine, histidine, leucine, lysine, and valine) and a decreased tissue level of the essential amino acids threonine and phenylalanine. Taurine, gamma-aminobutyric acid, alanine, glycerophosphoethanolamine and phosphoethanolamine also increased, whereas the aspartic acid concentration declined. When aerobic perfusion was resumed, the total pool of essential amino acids continued to increase and was nearly twice normal after 120 min of reperfusion. The combined concentration of asparagine and glutamine, serine, alpha-aminobutyric acid, and cystathionine also increased during postanoxic perfusion. Only taurine and phenylalanine concentrations returned toward normal.

Amino Acids↗
PubMed1977

Nutrient transport systems in dog brain.

The cerebral circulation of the dog was isolated and an extracorporeal system was used to perfuse the brain with diluted blood. Transport of blood-borne substances was investigated by measurement of arteriovenous (a-v) differences (net transport) and by the indicator dilution method (unidirectional influx). The net movement of amino acids between blood and brain was qualitatively and quantitatively different when measured by whole blood a-v differences than when measured by plasma a-v differences. This result suggests that erythrocytes are involved in the movement of amino acids between the blood and brain, a finding similar to that observed in other vascular beds (Elwyn et al. Am. J. Physiol. 222: 13338 1972). The transport of 13 different blood-borne substances was investigated at normal and elevated solute concentrations using the indicator dilution method. Saturable processes were observed for the unidirectional transport of tyrosine, tryptophan, L-dopa, free palmitic acid, adenine, thymine, adenosine, and guanosine. However, the blood-brain interface did not appear to contain a carrier for dopamine, folic acid, cyanocobalamin, guanine, hypoxanthine, and free oleic acid.

Adenine↗
PubMed1976

The characteristics of glucose transport across the blood brain barrier and its relation to cerebral glucose metabolism.

The evidence suggests that glucose transport across the blood brain barrier (BBB) in the dog is normally not a rate-limiting step in cerebral metabolism; however, transport may become rate-limiting under conditions of extreme hypoglycemia or anoxia. Studies on the mechanism of glucose transport from blood to brain do not at this time permit us to distinguish between active transport and facilitated diffusion; however, a decrease in the rate of unidirectional transport during anoxia suggests that an energy-dependent process may be involved. In spite of this evidence, glucose transport across the BBB is similar to the facilitated diffusion of glucose into the red cell in terms of the structural requirements of the glucose molecule, the pattern of inhibition by phlorizin, phloretin and cytochalasin B, and the lack of sensitivity to Na+ or insulin.

Animals↗
PubMed1976

Relationship of cerebral oxygen uptake to EEG frequency in isolated canine brain.

Cerebral oxygen uptake was correlated with electroencephalographic (EEG) frequency and amplitude in 87 isolated canine brains. Group I (71 brains) was perfused with diluted blood and Group II (16 brains) was perfused with whole blood equilibrated with oxygen at various partial pressures. The EEG's were classified as follows: A, highest frequency greater than or equal to 17 Hz, alpha (8-13 Hz) amplitude less than 50 muv, delta (less than or equal to 3.5 Hz), amplitude less than 100 muv; B, highest frequency greater than or equal to 17 Hz, alpha amplitude greater to or equal to 50 muv, and/or delta amplitude greater than or equal to 100 muv. C, highest frequency 8-16 Hz, alpha amplitude greater than or equal to 25 muv, and delta amplitude greater than 100 muv, D, highest frequency 0.5-16 Hz, alpha, if present, amplitude less than 25 muv, and/or delta amplitude less than 100 muv, and E, highest frequency 0-16 Hz, alpha, if present, amplitude less than 10 muv, and/or delta amplitude less than 15 muv. The Group I oxygen uptakes in ml/100 g of brain per min+/-SE for the five EEG classifications were A, 4.39+/-0.06, B, 4.13+/-0.08, C, 3.76+/-0.09, D, 3.40+/-0.12, and E, 2.55+/-0.06, whereas the corresponding Group II values were A, 4.64+/-0.22, B, 4.28+/-0.15, C, 3.82+/-0.24, D, 3.39+/-0.40, and E, 1.38+/-0.42. As the EEG deteriorates, cerebral oxygen uptake tends to decrease in a significant and parallel manner in both the diluted and whole blood groups.

Animals↗
PubMed1975

Inhibition of glucose transport into brain by phlorizin, phloretin and glucose analogues.

An indicator dilution technique with 22Na+ as the intravascular marker was used to measure unidirectional transport of D-[6-3H]glucose from blood into the isolated, perfused dog brain. 18 compounds which are structurally related to glucose were tested for their ability to inhibit glucose transport. The data suggest that no single hydroxyl group is absolutely required for glucose transport, but rather that glucose binding to the carrier probably occurs through hydrogen bonding at several sites (hydroxyls on carbons 1, 3, 4 and 6). In addition, alpha-D-glucose has higher affinity for the carrier than does beta-D-glucose. A separate series of experiments demonstrated that phlorizin and phloretin are competitive inhibitors of glucose transport into brain; however, phloretin is partially competitive and inhibits at lower concentrations than does phlorizin. Inhibition by phlorizin and phloretin is mutually competitive, indicating that these compounds compete for binding to the glucose carrier. Comparison with the results reported in the literature for similar studies using the human erythrocyte demonstrates a fundamental similarity between glucose transport systems in the blood-brain barrier and erythrocyte.

Animals↗
PubMed1975

Accelerative exchange diffusion kinetics of glucose between blood and brain and its relation to transport during anoxia.

An earlier study showed that unidirectional glucose transport from blood to brain decreases during perfusion with anoxic blood (Betz, A. L., Gilboe, D. D. and Drewes, L. R. (1974) Brain Res. 67, 307-316). Brain glucose levels also decrease during anoxia. Therefore, the present study was designed to investigate whether the decreased transport might be the result of decreased accelerative exchange diffusion when brain glucose levels are low. The rate of undirectional transport into brain (v) of D-[6-3H]glucose was studied in 22 isolated, perfused dog brains by means of an indicator dilution technique using 22Na as the intravascular reference. The kinetics of transport were determined over a range of blood glucose concentrations (S1) at each of five different brain glucose levels (S2). The existence of accelerative exchange diffusion for glucose was indicated by a decrease in the intercept (increase of apparent V) of a double reciprocal plot (1/v versus 1/S1) as S2 increased. This phenomenon is consistent with a model for facilitated diffusion in which the mobility of the loaded carrier is greater than that of the unloaded carrier. Although the data predict a decrease in glucose transport during anoxia, the predicted decrease (5%) is less than the observed decrease (35%). It is concluded that the simple mobile-carrier model for facilitated diffusion cannot, by itself, describe all properties of blood-brain glucose transport.

Animals↗
PubMed1975

Kinetics of unidirectional leucine transport into brain: effects of isoleucine, valine, and anoxia.

The rate of unidirectional uptake, v, of L-[4,5-3H]leucine was studied in 17 isolated dog brains by means of an indicator-dilution technique using 22Na as the intravascular reference. The arterial leucine concentration was varied in increments by adding unlabeled leucine to the blood and v was determined after each change. The valine and isoleucine concentrations were varied independently to permit evaluation of their effect on leucine transport. A preliminary analysis indicated that both valine and isoleucine are competitive inhibitors. Therefore, all data were fitted to an equation that describes Michaelis-Menten kinetics in the presence of two competitive inhibitors. These calculations yielded an apparent Km for leucine transport of 1.58 mM plus or minus .28 SE, a V max of 0.323 mumol/g per min plus or minus .035 SE, and an apparent K i for inhibition of leucine transport of 1.76 mM plus or minus .34 SE for valine and 0.73 mM plus or minus .14 SE for isoleucine. In four isolated brains perfused with blood having a constant leucine level, indicator-dilution injections were made before, and at 1, 5, and 10 min after the start of perfusion with anoxic blood. These findings showed that, unlike glucose transport (Brain Res. 67: 307-316, 1974), the rate of lucine transport is unaffected by 10 min of anoxia.

Animals↗