Glutamate dehydrogenase isoforms with N-terminal (His)6- or FLAG-tag retain their kinetic properties and cellular localization

Glutamate dehydrogenase (GDH) is a crucial enzyme on the crossroads of amino acid and energy metabolism and it is operating in all domains of life. According to current knowledge GDH is present only in one functional isoform in most animals, including mice. In addition to this housekeeping enzyme (hGDH1 in humans), humans and apes have acquired a second isoform (hGDH2) with a distinct tissue expression profile. In the current study we have cloned both mouse and human GDH constructs containing FLAG and (His)6 small genetically-encoded tags, respectively. The hGDH1 and hGDH2 constructs containing N-terminal (His)6 tags were successfully expressed in Sf9 cells and the recombinant proteins were isolated to ≥95 % purity in a two-step procedure involving ammonium sulfate precipitation and Ni(2+)-based immobilized metal ion affinity chromatography. To explore whether the presence of the FLAG and (His)6 tags affects the cellular localization and functionality of the GDH isoforms, we studied the subcellular distribution of the expressed enzymes as well as their regulation by adenosine diphosphate monopotassium salt (ADP) and guanosine-5'-triphosphate sodium salt (GTP). Through immunoblot analysis of the mitochondrial and cytosolic fraction of the HEK cells expressing the recombinant proteins we found that neither FLAG nor (His)6 tag disturbs the mitochondrial localization of GDH. The addition of the small tags to the N-terminus of the mature mitochondrial mouse GDH1 or human hGDH1 and hGDH2 did not change the ADP activation or GTP inhibition pattern of the proteins as compared to their untagged counterparts. However, the addition of FLAG tag to the C-terminus of the mouse GDH left the recombinant protein fivefold less sensitive to ADP activation. This finding highlights the necessity of the functional characterization of recombinant proteins containing even the smallest available tags.

Genome-wide association study of migraine implicates a common susceptibility variant on 8q22.1

Migraine is a common episodic neurological disorder, typically presenting with recurrent attacks of severe headache and autonomic dysfunction. Apart from rare monogenic subtypes, no genetic or molecular markers for migraine have been convincingly established. We identified the minor allele of rs1835740 on chromosome 8q22.1 to be associated with migraine (p=5.12 × 10⁻⁹, OR 1.23 [1.150-1.324]) in a genome-wide association study of 2,748 migraineurs from three European headache clinics and 10,747 population-matched controls. The association was replicated in 3,202 cases and 40,062 controls for an overall meta-analysis p-value of 1.60 × 10⁻¹¹ (OR 1.18 [1.127 – 1.244]). rs1835740 is located between the astrocyte elevated gene 1 (MTDH/AEG-1) and plasma glutamate carboxypeptidase (PGCP). In an expression quantitative trait study in lymphoblastoid cell lines transcript levels of the MTDH/AEG-1 were found to have a significant correlation to rs1835740. Our data establish rs1835740 as the first genetic risk factor for migraine.

Oxygen dependence of tyrosine hydroxylase

The effects of dioxygen on tyrosine hydroxylase (TH) activity was studied, measuring the formation of DOPA from tyrosine, (3)H(2)O from 3,5-(3)H-tyrosine, or by direct oxygraphic determination of oxygen consumption. A high enzyme activity was observed during the initial 1-2 min of the reactions, followed by a decline in activity, possibly related to a turnover dependent substoichiometrical oxidation of enzyme bound Fe(II) to the inactive Fe(III) state. During the initial reaction phase, apparent K (m)-values of 29-45 microM for dioxygen were determined for all human TH isoforms, i.e. 2-40 times higher than previously reported for TH isolated from animal tissues. After 8 min incubation, the K (m) (O(2))-values had declined to an average of 20 +/- 4 microM. Thus, TH activity may be severely limited by oxygen availability even at moderate hypoxic conditions, and the enzyme is rapidly and turnover dependent inactivated at the experimental conditions commonly employed to measure in vitro activities.

Reduced autonomic activity during stepwise exposure to high altitude

Several studies have shown increased sympathetic activity during acute exposure to hypobaric hypoxia. In a recent field study we found reduced plasma catecholamines during the first days after a stepwise ascent to high altitude. In the present study 14 subjects were exposed to a simulated ascent in a hypobaric chamber to test the hypothesis of a temporary reduction in autonomic activity. The altitude was increased stepwise to 4500 m over 3 days. Heart rate variability (HRV) was assessed continuously in seven subjects. Baroreceptor reflex sensitivity (BRS) was determined in eight subjects with the 'Transfer Function' method at baseline, at 4500 m and after returning to baseline. Resting plasma catecholamines and cardiovascular- and plasma catecholamine- responses to cold pressor- (CPT) and mental stress-test (MST) were assessed daily in all and 12 subjects, respectively. Data are mean +/- SEM. Compared with baseline at 4500 m there were lower total power (TP) (35 457 +/- 26 302 vs. 15 001 +/- 11 176 ms2), low frequency (LF) power (3112 +/- 809 vs. 1741 +/- 604 ms2), high frequency (HF) power (1466 +/- 520 vs. 459 +/- 189 ms2) and HF normalized units (46 +/- 0.007 vs. 44 +/- 0.006%), P < or = 0.001. Baroreceptor reflex sensitivity decreased (15.6 +/- 2.1 vs. 9.5 +/- 2.6 ms mmHg(-1), P = 0.015). Resting noradrenaline (NA) decreased (522 +/- 98 vs. 357 +/- 60 pmol L(-1), P = 0.027). The increase in systolic blood pressure (SBP) and NA during mental stress was less pronounced (21 +/- 4 vs. 10 +/- 2% and 25 +/- 9 vs. -2 +/- 8%, respectively, P < 0.05). The increase in SBP during cold pressor test decreased (16 +/- 3 vs. 1 +/- 6%, P = 0.03). Diastolic blood pressure, HR and adrenaline displayed similar tendencies. We conclude that a transient reduction in parasympathetic and sympathetic activity was demonstrated during stepwise exposure to high altitude.

[Should iron preparations be available only by prescription?]

Many persons associate fatigue and lassitude with iron deficiency and take extra iron "to be on the safe side". This is an unfortunate practice, as the early symptoms of iron deficiency anaemia and of hereditary iron overload (homozygous primary haemochromatosis) are similar. Primary haemochromatosis is considerably more prevalent than earlier believed. As many as 5 per 1,000 of the Norwegian population may have two mutated genes for haemochromatosis, while up to 15% may be carriers of a single mutated gene, and for these an extra intake of iron may be hazardous. The condition is highly underdiagnosed. In Norway at present, iron preparations of 60-100 mg are sold over the counter in pharmacies without prescription and often by self-service. However, no one should use iron tablets until iron deficiency and its cause has been ascertained. To avoid uncritical use of iron, iron preparations should be available only by doctor's prescription. Prolonged abuse of iron tablets may result in secondary haemochromatosis.

[Thomas H.Huxley--the naval doctor who became Darwin's bulldog]

Thomas H. Huxley (1825-1895) was an English physician and biologist who had a deep impact on the Victorian age. More than any other at his time he introduced scientifically based values. As a member of London's school board he brought science into the curriculum, encouraging school-children to ask questions and to make their own observations. Huxley came from a lower middle class family with little money. By sheer determination and hard work he managed to get a medical education at Charing Cross Hospital Medical School. He then obtained a posting on H.M.S. Rattlesnake, which gave him a chance to explore the southern seas and to study marine species. The results were published by the Royal Society of which Huxley became a member at the age of 26, and later its president. After several years of uncertainty he secured a position at the Royal School of Mines, which he transformed into the Imperial College of Science. He was a prolific scientist with wide interests, doing valuable work in paleontology, taxonomy and ethnology. Huxley wrote numerous essays on philosophy and scientific subjects. He coined the word agnostic to explain his attitude to Christian dogma. His style was clear and direct, and his essays still read very well. However, Huxley is now mostly, perhaps unfairly, remembered for his defence of Darwin's theory of evolution. In his book Evidence as to man's place in nature, Huxley, in contrast to Darwin, deals with the evolution of humans, mainly based on comparative anatomy. Huxley advocated a firmly held belief that scientific truths will have a liberating effect on the minds of men. His lectures on scientific subjects attracted large audiences of people who had not had the benefit of a higher education.

[Dr Alexander M. Kellas and the first Mount Everest expedition]

In 1921 the government of Tibet gave permission for a British party to attempt Mount Everest from the northern Tibetan side. Little was known about the physiological and medical problems associated with ascents to extreme altitudes. The person who knew most about these topics was Dr. Alexander Kellas, lecturer in medical chemistry at the Middlesex Hospital Medical School. He had made a number of expeditions to the Sikkim Himal and the Tibetan border before the first world war, and had become increasingly interested in the problems caused by altitude. He was invited to join the Everest expedition but died on the approach march at Kampa Dzong on the Tibetan plateau, within sight of the mountain. Before he went on the expedition Kellas wrote an article entitled A consideration of the possibility of ascending Mt. Everest. This paper was never published, but the manuscript exists in the archives of the Royal Geographical Society and the Alpine Club in London. As Kellas saw it, the main issue was whether sufficient adaptation could occur to allow a climber to ascend from a camp at about 7,700 m to the summit (8,848 m) in one day without supplementary oxygen. His conclusion was that this was possible and, in fact, the first such ascent by Habeler and Messner in 1978 started from a camp at 7,900 m. Kellas calculated the pressure on the summit to be 251 mmHg, a more accurate figure than estimates based on the "Standard Atmosphere" Kellas estimated maximum oxygen uptake at the summit to be 970 ml/min, and the current value is thought to be about 1,070 ml/min. His estimates of the climbing rate near the summit closely parallels the rate of Habeler and Messner. Kellas had a talent for asking the right questions. He applied his considerable knowledge of physiology to the topic of high altitude, and his suggestions and recommendations were of consistently high quality. He deserves to be better known, both for his geographical surveys and for his pioneer work on high altitude medicine and acclimatisation. The 1921 expedition, after many failed attempts, discovered a possible route to the top of Mount Everest, which was used on all the summit attempts between the two world wars. The route went from Kharta, over the pass Lhakpa La, across East Rongbuk glacier and up via the north col.

[Chaos and fractals. Are these of interest to medical science?]

Biological systems are governed by nonlinear dynamics and often appear to be random, because the available information, though accurate, is usually incomplete. It is important to be aware of the fact that nonlinear deterministic systems can behave unpredictably in the long term. Traditional reductionism is unable to provide an adequate understanding of such systems. A more global description and explanation of forms, features and functions is required. Chaos theory and fractal geometry are of value in this respect. This article is an introduction to this relatively new field of science and mathematics.

Endothelin-1-induced increases in microvascular permeability in isolated, perfused rat lungs requires leukocytes and plasma

Effect of endothelin-1 (ET-1) (10(-8) M) on pulmonary microvascular permeability was examined in isolated rat lungs perfused with blood or various blood components. Microvascular permeability was assessed by measuring fluid filtration rate (FFR) in lungs pretreated with papaverine in order to prevent changes in vascular smooth muscle tone. ET-1 significantly increased FFR (131.0 +/- 10.1 mg/min, P < 0.01) after perfusion with blood for 60 min. In lungs perfused with leukocytes resuspended in plasma, ET-1 increased FFR significantly both 30 min (40.4 +/- 11.4 mg/min, P < 0.01) and 60 min (97.4 +/- 14.5 mg/min, P < 0.01) after it was added to the perfusate. Heat inactivation (56 degrees C; 1 hr) of plasma did not attenuate this effect of ET-1 (94.4 +/- 25.1 mg/min, P < 0.01). When lungs were perfused with leukocytes resuspended in Krebs Ringer albumin instead of plasma, or with plasma only, ET-1 did not cause any change in FFR. In conclusion, ET-1 increases microvascular permeability in isolated blood-perfused rat lungs. The effect is critically dependent on the presence of leukocytes and plasma components other than complement.

Effects of exercise and CO2 inhalation on the breathing pattern in man

Conflicting opinions exist concerning the breathing pattern in man during resting and stimulated ventilation. Some but not all investigators have reported the existence of an abrupt change, a 'breakpoint', in the relation between mean tidal volume and mean inspiratory time. Different opinions exist as to whether the slope and the intercept for the relation between mean minute ventilation and mean tidal volume are identical regardless of the mode of stimulating the ventilation. We have studied 10 subjects, at rest and during graded stimulation of ventilation by CO2 inhalation and exercise. No breakpoint was observed in the relations between (1) mean tidal volume and mean inspiratory time and (2) mean tidal volume and mean expiratory time, even if a wide range of tidal volumes was achieved in our subjects. Carbon dioxide inhalation (normoxic or hyperoxic) and exercise gave different regression lines for the relation between mean minute ventilation and mean tidal volume in 8 out of 10 subjects with a larger slope during exercise. At exercise inspiratory time decreased with any increase in tidal volume, while during CO2 breathing no consistent change in inspiratory time was seen. Mean inspiratory flow was linearly related to exercise load and apparently also to arterial carbon dioxide pressure. We conclude that CO2 breathing gives a breathing pattern which is different from that obtained with exercise in the majority of normal subjects. Furthermore, we could not confirm the existence of breakpoints in relations describing the breathing pattern of normal man.

Arterial P CO2 and lung ventilation in man exposed to 1-5% CO2 in the inspired gas

Conflicting results have been published on the shape of the curve relating the change in lung ventilation to the change in alveolar or arterial PCO2 induced by increased inspired CO2 (the CO2 sensitivity). In this study eight human subjects with in-dwelling arterial cannulae were each exposed to five different levels of increased inspired CO2 (1-5%). Arterial PCO2 and ventilation were measured in the 7th minute of each period of CO2 exposure. Each CO2 exposure period was flanked by control periods in which similar measurements were carried out during air breathing. We found non-linear increases in both ventilation and arterial PCO2 with increasing levels of inspired CO2. When 5% CO2 in air was inspired the arterial PCO2 increased by about 15% of the inspired CO2 load. There was no significant non-linearity in the relation between change in alveolar ventilation (normalized to body surface) and change in arterial PCO2. The inter-individual variation in CO2 sensitivity was less when alveolar ventilation was normalized to the CO2 output rather than to body surface area. We conclude that the sensitivity to CO2 is close to constant within the range 0-5% CO2 in the inspired gas.

CO2 sensitivity in humans breathing 1 or 2% CO2 in air

Ventilation increases when the concentration of CO2 in the inspired gas is increased, thereby limiting the increase in alveolar and arterial PCO2. The extent of this compensation at low levels of inspired CO2 has been debated. In five healthy humans, we have measured arterial PCO2, arterial pH and ventilation during exposure to 1 and 2% CO2 in the inspired gas. Each exposure lasted at least 7 min and arterial blood was sampled over at least 30 s during the last minute of each period. The ventilation was measured in the sixth and seventh min. The protocol included the sequences: control-test-control and test-control-test with 'test' representing CO2 loading and 'control' 0% CO2, respectively. We found that arterial PCO2 increased and pH decreased at both levels of inspired CO2. The mean increase in arterial PCO2 was 0.09 and 0.25 kPa, at CO2 1 and 2%, respectively. Three subjects were exposed to 1% CO2 in the inspired gas for 28 min flanked by similar control periods. In each period arterial blood samples were taken at 2- or 3-min intervals. Arterial PCO2 remained elevated for at least 20 min during the CO2 loading. The sensitivity to CO2 (ratio of increase in ventilation to increase in arterial PCO2) was within the range described by others at higher levels of inspired CO2. Arterial PCO2 increased by about 10% of the imposed load. We conclude that the increase in ventilation provides only incomplete compensation for exposure to CO2: arterial CO2 is increased and arterial pH decreased also at very low levels of inspired CO2.

Changes in human cerebral blood flow due to step changes in PAO2 and PACO2

The effect of moderate hypoxia on cerebral blood flow (CBF) in man has not been well described, and little is known about the interaction of changes in arterial PO2 and PCO2 as regards CBF. Using a non-invasive doppler ultrasound method we have measured the instantaneous mean blood velocity (which is proportional to CBF as long as the cross-section of the vessel is constant) in the carotid artery in four healthy unanaesthetized subjects. We found in all subjects that a reduction in alveolar PO2 from about 13 to about 8.7 kPa with maintained constant alveolar PCO2 (PA, CO2) caused CBF to increase gradually over 10 min (half-time about 4 min) to about 125% of control. The CBF decreased quickly (half-time about 45 s) towards control when alveolar PO2 was reset to 13 kPa. As measured 5 min after a step-change in PA, O2, the change in CBF was independent of PA, CO2 within the range 3.3-6.7 kPa. An increase in PA, O2 to about 33 kPa reduced CBF only if PA, CO2 was in the hypercapnic range. Unexpectedly we found that the CBF response showed 'adaptation' during both maintained increase and decrease in PA, CO2. The CBF started to return towards control level within 10 min after induction of hypo- or hypercapnia. We conclude that also moderate hypoxia causes increased CBF in unanaesthetized man within a wide range of PA, CO2.

Cardiovascular responses to face immersion and apnea during steady state muscle exercise. A heart catheterization study on humans

The cardiovascular adjustments to face immersion and apnea (FIA) in human beings during steady-state muscle exercise (163 and 98 watt) have been investigated. Using a triple lumen flow directed catheter inserted into the pulmonary artery we were able to measure cardiac output (CO) by thermodilution technique, pulmonary arterial pressure (PPA) right atrial pressure (PRA) and left ventricular filling pressure (PAD). Phasic arterial blood pressure (BP) was measured via a cannula in the radial artery. A 12 lead ECG was recorded continuously. FIA caused an immediate rise in BP (median 61%), the highest level being 25.33 kPa. CO during the last half of FIA was reduced by 49% (range 46-59, n = 7) systemic vascular resistance increased by median 200% (range 111-280). Myocardial oxygen demand determined by the heart rate pressure double product fell from median 33.6 to 16.8 (163 W) and 28.5 to 19.1 (98 W) given as beats/min X kPa X 10(2). Mean reduction was by 42%. PPA and PRA immediately increased and remained constant until a further pronounced increase was seen towards the end of FIA when pulmonary vascular resistance (PVR) went up. PACO2 and PAO2 at the end of 30 sec FIA (163 W) was 10.0 and 5.6 kPa, respectively, values which expectedly would cause pulmonary vasoconstriction. Our findings demonstrate that humans are able to make principally the same cardiovascular adjustments to diving as aquatic mammals, although the response patterns are slower and less efficient.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute effects of acetazolamide on cerebral blood flow in man

We have followed the time course of the effect of the carbonic anhydrase inhibitor acetazolamide injected i.v. in unanesthetized healthy human beings. The dose administered was 500 mg as a bolus. Cerebral blood flow (CBF) was measured continuously before, during and after the injection, using a pulsed ultrasound doppler system, which measured the instantaneous mean velocity across the lumen of the internal carotid artery, just below its entrance into the skull. Ventilation, heart-rate, end-expiratory PCO2, arterial PCO2, pH and systemic blood pressure was also measured. We found that acetazolamide caused a rise in CBF which could be detected as early as 2 min after the injection. A maximal average response of 75% increase in CBF was seen after 25 min. The half-time of the declining phase of the response was 95 min. There were no systematic differences in the CO2 reactivities, given as delta CBF/delta PACO2 in % of CBF at normocapnia, before and after acetazolamide injection, regardless of the absolute PACO2 level. The present dose of the drug caused no change in ventilation, alveolar and arterial PCO2 or in arterial blood pH indicating that the carbonic anhydrase was not fully inhibited. Our observations show that acetazolamide nevertheless caused a rapid vasodilation in the brain and over a wide range of PCO2's. We suggest that this agent has a local vasodilator effect on the cerebral arterioles, unrelated to its specific effects as a carbonic anhydrase inhibitor.

Fluid Exchange in the isolated perfused lung

The advantages of an isolated, perfused lung preparation in studies of transvascular fluid shifts are described. We find the permeability characteristics of the exchange vessels in the rabbit lung preparation to be similar to those obtained in lungs in situ. The filtration coefficient is similar during plasma and during Krebs-Ringer dextran T 70 perfusion. Therefore proteins in the perfusate do not modify the permeability of the exchange vessels in these lungs as had been reported for other vascular beds. Interstitial fluid pressure in both the alveolar walls and the alveolar corner regions increases with a rise in alveolar pressure. The result is a reduction in the fluid filtration rate under both zone-III and zone-I conditions. The resistance of the extravascular pathway and the fluid pressure in the periarterial/perivenous spaces both appear to be reduced when lung volume is increased by a reduction in pleural pressure. The net effect of positive airway pressure on the transvascular fluid exchange will depend on the relative contribution of the alveolar pressure effects and the lung volume effects. Fluid reabsorption can be observed to occur in the isolated, perfused rabbit lung. This reabsorption does not take place at the level of the loose perivascular tissue spaces since the interstitial fluid pressure at these sites is much lower than the microvascular pressure. We suggest that fluid reabsorption takes place at the thick part of the air-blood barrier, which, most likely, has a higher fluid pressure.

Changes in cerebral blood flow during hyperventilation and CO2-breathing measured transcutaneously in humans by a bidirectional, pulsed, ultrasound Doppler blood velocitymeter

We have used a bidirectional pulsed ultrasound doppler system which measures the instantaneous mean velocity across the lumen of a blood vessel in order to determine the relationship between alveolar PCO2 (PACO2) and blood flow in the four arteries supplying the brain in humans. Both high and low PACO2-values were explored. Six subjects, 3 males and 3 females (22-40 years) were studied by use of this non-invasive technique. To increase the PACO2 the subjects were breathing 4, 6 and 8% CO2 in air. PACO2 was reduced by voluntary hyperventilation down to a chosen end-expiratory PCO2 value of about 2.2 kPa. We found a linear relationship between arterial blood flow expressed as a percentage of control level and PACO2 in the range from 3.3 to 7.3 kPa. At the very lowest PACO2 values a levelling off of the response, with flow values of 40 to 45%, was observed. The CO2-reactivities in the 6 persons varied between 28.1 and 30.0%/kPa. The time course and the magnitude of the flow response were similar in all four arteries.

The pulmonary vasoconstrictor response to hypoxia. The hypoxia-sensitive site studied with a volatile inhibitor

Recent investigations have revealed that a number of inhalation anesthetics, including halothane, inhibit the pulmonary vasoconstrictor response to hypoxia without affecting other vasoconstrictor stimuli. Various injectable anesthetics do not show this effect. This discrepancy could be due either to different pharmacological properties or to the different routes of administration. There is no general agreement on whether the response to hypoxia is elicited mainly by airway hypoxia or by blood hypoxemia, i.e. where within the lungs hypoxia acts. This work is an attempt to localize the hypoxia-sensitive site employing halothane. We have studied the reduction of standardized vasoconstrictor responses to hypoxia during administration of halothane via: (1) the airways, (2) the pulmonary artery and (3) the pulmonary veins (backward perfusion). Our experimental model has been two pairs of series-perfused hyperventilated isolated rat lungs. An equimolar concentration of halothane most effectively inhibits the response when presented to the alveoli, less when presented to the arterial- and least when presented to the venous segments of the pulmonary vasculature. We suggest that the response to hypoxia is inhibited by halothane at some extravascular site on the arterial side of the pulmonary vasculature, functionally closer to the alveoli than to the responding vessels. A model which combines all the data into an unifying concept has been presented.

Pulmonary O2 transfer during pulsatile and non-pulsatile perfusion

The importance of the perfusion pattern for the oxygen transfer has been examined in isolated rabbit lungs perfused with plasma at constant volume inflow. The lungs were ventilated with constant tidal volume and constant end-expiratory pressure. Following a standardized rise in FIO2 the rate of rise in pulmonary venous PO2 (delta PO2/delta t) was measured during alternately pulsatile and non-pulsatile perfusion in normal lungs and in lungs made edematous by elevation of left atrial pressure. In normal lungs there was no difference in delta PO2/delta t when the two modes of perfusion were compared. In edematous lungs delta PO/delta t was statistically higher during pulsatile perfusion, indicating a beneficial effect of flow- and pressure pulsations, e.g. a better distribution of V/Q ratios throughout the lungs. In a separate series of expts. the advancement of a high O2 front through the airways was measured, and the two perfusion patterns compared. Since no difference was found, we suggest that the phenomenon of "cardiogenic gas mixing" in the airways in vivo is a result of a direct action of the heart on the lungs rather than arterial pulsations.

Constant flow- vs. constant pressure-perfusion for studies of pulmonary vasoactive responses

We have compared the pulmonary vascular responses to a standardized hypoxic vasoconstrictor stimulus (FIO2 = 0.02) obtained during 1) constant volume inflow, with pulmonary arterial pressure as the dependent variable, and 2) constant inflow pressure, with flow as the dependent variable. Isolated rat lungs were perfused at different baseline transvascular pressures. The experimental arrangement allowed changes between the two types of perfusion. Hypoxia at constant pressure perfusion gave a higher percentage rise in pulmonary vascular resistance (PVR) at all pressure levels. This advantage was however, more than offset by the finding that a) vascular closure (total or partial) often occurred, particularly below arterial pressure of 3 kPa, making detection of graded responses impossible, and b) the control situation was rarely regained. Responses obtained during constant flow were less reduced by elevations in baseline transvascular pressure, and the control situtaion was rapidly and completely regained. The observation that hypoxic vascular closure may occur in the pulmonary vascular bed supports the hypothesis that high altitude edema is caused by precapillary occlusion of a major part of the vascular bed, thereby subjecting still perfused regions to very high pressure and flow.

Vascular resistance in atelectatic lungs: effects of inhalation anesthetics

We have investigated the relative contribution of mechanical obstruction and hypoxia-induced vasoconstriction to the increased pulmonary vascular resistance (PVR) in atelectatic lungs. For this purpose we have utilized the previous observation that inhalation anesthetics inhibit the vasoconstrictor response to pulmonary hypoxia. The effects of halothane, enflurane and ether on PVR in atelectatic lungs have been explored. Two pairs of isolated rat lungs were perfused in series at constant flow. One of the preparations was made atelectatic by airway occlusion subsequent to ventilation with a high PO2 gas (95% O2). Ventilation of the other preparation continued with hypoxic gas (2% O2), resulting in a gradual increase in PVR in both preparations. When maximum PVR was reached, one of the above inhalation anesthetics was administered to the atelectatic lungs via the ventilated lung preparation. This caused a dose-dependent, reversible reduction of PVR. The same effect was observed when pulmonary arterial PO2 was increased (greater than 66.5 kPa). Histological examination revealed that two out of four preparations were completely atelectatic 1 h after airway occlusion, whereas atelectasis was nearly complete in the other two. In two groups, airways were occluded for 1 h. In the first group PVR increased to 163% (median) above baseline level, as found during ventilation with high PO2. High arterial PO2 reduced PVR in the atelectatic lungs to 50% (median) above baseline, whereas papaverine induced a further PVR reduction, to 7% (median) above baseline. In the other group, papaverine was given before airway occlusion, and PVR increased to 10% (median) above baseline. Comparison of the two groups shows that mechanical obstruction accounts for about 6% (10/163) of the overall rise in PVR during atelectasis.

Determinants of transvascular fluid shifts in zone I lungs

We studied the fluid shifts in isolated, plasma-perfused rabbit lungs kept completely within zone I. The rate of fluid filtration or reabsorption was determined gravimetrically. A rise in alveolar pressure at constant pleural and vascular pressures reduced th rate of filtration or increased the rate of reabsorption in seven of eight lungs. In seven of seven lungs a reduction in pleural pressure at constant alveolar and vascular pressures increased the rate of filtration or decreased the rate of reabsorption. Thus, a given rise in lung volume had opposite effects depending on whether this rise was caused by an increased alveolar or reduced pleural pressure. Therefore, the exchange vessels studied cannot be true extra-alveolar vessels, which always expand (reflecting a rise in transmural pressure) with a rise in lung volume. When alveolar and pleural pressures were equally increased at constant vascular pressure, the rate of filtration was reduced in four of four lungs. The results can be explained through the existence of exchange vessels situated neither in the alveolar septae proper nor among the true extra-alveolar vessels. The vessels in the alveolar junctions are the most likely candidates.

Hypoxia-induced pulmonary vasoconstriction: effects of fentanyl following different routes of administration

Recent investigations have revealed that intravenous anesthetics, including fentanyl, do not reduce the pulmonary vasoconstrictor response to alveolar hypoxia. In contrast, the response is markedly reduced or abolished by inhalation anesthetics. Recent investigations have demonstrated that the route of administration is of importance. Halothane, which inhibits the response when administered via the airways, behaves more like an intravenous anesthetic following administration via the blood stream, provided the alveolar concentration has been kept low (Bjertnaes et al. 1977). It was therefore a distinct possibility that the lack of any damping effect of fentanyl on the response could be due to the route of administration rather than to a different pharmacological property. We have tested this hypothesis by introducing fentanyl in nebulized form via the airways in one group of isolated rat lungs, and via the blood stream in another group. We found, however, no effect of fentanyl on the pulmonary vasoconstrictor response to hypoxia, regardless of the route of administration. Plasma concentrations of fentanyl were determined by radioimmunoassay and compared with those encountered in anesthetic practice.

The importance of flow pulsatility for the rate of transvascular fluid filtration in lungs

1. The rate of transvascular fluid filtration has been studied with a gravimetric technique in isolated perfused rabbit lungs during periods of elevated left atrial pressure (PLA). 2. Fluid filtration was expressed as the filtration coefficient, Kf (g/min x 100 g bloodless lung x mmHg PLA) and determined during alternately pulsatile and non-pulsatile perfusion in six zone III and three zone II/I lung preparations. Perfusion pattern was changed without interruption of flow. Mean in- and outflow pressures were kept constant. 3. In all the lungs it was found that Kf was higher during pulsatile than during non-pulsatile flow (P less than 0.01). Mean Kf (+/- S.E. of mean) for the zone III preparations was 0.42 (+/- 0.089) and 0.27 (+/- 0.057) for pulsatile and non-pulsatile perfusion, respectively. The corresponding figures for the zone II/I preparations were 0.11 (+/- 0.035) and 0.04 (+/- 0.030). 4. We suggest that the difference is due to a larger filtration area and/or a higher mean microvascular hydrostatic pressure during pulsatile than during non-pulsatile flow and not to a rise in hydraulic conductivity due to pressure pulsations ('stretched pores'). 5. When the water-exchange function of the lung is considered, flow pattern should be taken into account as an entity in its own right in addition to the steady state or the mean component of blood flow.

Prostaglandin content in blood and lung tissue during alveolar hypoxia

The aim of the present work was to investigate whether prostaglandins (PGs) are synthetized and released from isolated blood-perfused rat and cat lungs secondary to vasoconstriction induced by alveolar hypoxia. The lungs were perfused with autologous blood with constant volume inflow via the pulmonary artery in a recirculating system. They were ventilated with constant volume positive pressure, and acute alveolar hypoxia was induced by ventilation with a gas containing 2% O2. A superfusion bioassay technique was used to measure PG-like activity in the perfusate from the lungs, the blood being re-oxygenated before reaching the assay tissues. The oxygenator prevented the perfusate hypoxia induced by ventilation hypoxia to affect the bioassay tissues. The assay tissues were rat stomach strip, rat colon and chick rectum. They were sensitive to calibrating doses of 0.5--1 ng/ml PGE2 and 1--2 ng/ml PGF2alpha. In another series of experiments PGs of the F-series were measured in lung tissue from normoxic and hypoxic lungs with radioimmunoassay technique. No increase in PG-like activity could be detected in the venous effluent by means of bioassay during hypoxia, nor was the lung tissue content of immunoactive PGF increased by hypoxia. The present findings indicate that alveolar hypoxia does not stimulate PG-synthesis in lungs, refuting that PGs are important mediators of the pulmonary vasoconstrictor response to alveolar hypoxia. It is concluded that PGs play no significant role in producing the pressor response to alveolar hypoxia.

Hydrostatic pulmonary edema in the cat. Effects on pulmonary blood and water volumes and on lung compliance

The effect on lung compliance of changes in intra- and extravascular volumes has been studied. Such changes were induced by inflation and deflation of a balloon placed in the left atrium in open-chest cats. Blood constituents were labeled with isotopes, and tissue water content was found from the wet/dry labeled with isotopes, and tissue water content was found from the wet/dry weight ratio. When left atrial pressure (PLA) was elevated to a value not exceeding 32 mmHg (4.256 kPa), there was only a minute increase in tissue water volume, and we observed a reversible reduction in lung compliance related to the rise in lung blood volume. At higher PLA, a rapid rise occurred in extravascular fluid volume, with evidence of alveolar flooding. Earlier experiemtns have shown that, in isolated perfused lung, a situation of slow, steady increase in interstitial fluid can be created. This does not seem to be the case with lungs in situ: once the lymphatic drainage is unable to cope with transvascular fluid flow, an unstable situation is created. This rapidly leads to alveolar flooding and a fall in compliance in addition to that caused by a rise in blood volume. From our fluid and pressure determinations, we calculated a filtration coefficient (Kf) of 0.45 ml/100 g wet lung X cmH2O X h. This is within the range reported for sheep lungs. Observation of dynamic lung compliance cannot be used for detection of interstitial fluid accumulation. It appears, however, that in contrast to isolated lungs, this phase of edema-formation rapidly leads to alveolar flooding.

Small airway constriction and closure after induced intravascular platelet aggregation

The aim of this study was to investigate the function of the peripheral airways after intravascular platelet aggregation induced by i.v. infusions of collagen in open chest anesthetized cats, ventilated with constant tidal volume. Lung compliance was examined under static conditions (stat CL) and under dynamic conditions (dyn CL) at ventilation frequencies of 5, 24 and 50/min. In the control situation dyn CL 24 was approximately 90% of stat CL. Collagen infusions resulted in a pronounced frequency-dependence of lung compliance. When dyn CL 24 had decreased by approximately 40% a reduction in stat CL could also be detected. When dyn CL 24 decreased even more a concurrent reduction in stat CL was evident. These findings indicate that the initial event after induced intravascular platelet aggregation is small airway constriction. With more pronounced changes airway closure and reduction in lung volume occurs. We suggest that these functional changes in peripheral airways result in the impaired gas exchange known to occur after intra-vascular platelet aggregation.

[Experiences with various antireflux operations (author's transl)]

One hundred and thirty-eight antireflux operations in 94 patients are reported from 1964 to 1974. Bischoff's method was used 44 times with 63% successful results; Lich/Grégoir's method 38 times with 77% success; and Politano/Leadbetter's method 50 times with 92% success. Indications are briefly investigated.

Alveolar pressure and lung volume as determinants of net transvascular fluid filtration

We have investigated the influence of changes in alveolar pressure (PAlv) and in lung volume on the net transvascular fluid filtration rate (FFR). The preparation was isolated, perfused zone III rabbit lungs. In observation periods the outflow pressure was kept constant at a level generally causing net filtration. All pressures were measured relative to atmospheric. FFR was measured by continuous monitoring of preparation weight. Elevation of Palv at constant lung volume caused reversible reductions in FFR, also at constant capillary hydrostatic pressure (Pa-V less than 2 Torr). Increases in lung volume at constant PAlv caused reversible increases in FFR. When both PAlv and Ptp were increased a reduction in FFR was seen in the majority of cases. We conclude that at constant pulmonary arterial pressure, the size and the direction of the influence of positive airway pressure on FFR depend on the relative change in lung volume and in alveolar pressure per se. Under the present experimental conditions a rise in PAlv will be transmitted to interstitial fluid pressure and affect the transvascular fluid balance.

Influence of moderate vasoconstriction on the wave reflection properties of the pulmonary arterial bed

Increased transmural pressure in the pulmonary arterial bed may reduce vascular input impedance and reduce hydraulic power linked to pulsatile blood flow. Vascular impedance and pulsatile hydraulic power (Wp) levels of isolated perfused rabbit lungs were compared after similar rises of pulmonary arterial pressure (PAp), induced either by vasoconstriction or by left atrial pressure (LAp) elevation. Resulting Wp levels were significantly smaller after vasoconstriction than LAp elevation. Wp showed a minimum level at physiologic PAp (about 20 cm H2O) irrespective of the cause of PAp elevation. Pressure pulse wave reflection coefficient (see article) was calculated for control and test situations, and was found to be approximately doubled after vasoconstriction. Only minor changes in (see article) were found after LAp elevation. Accordingly, moderate vasoconstriction (resulting PAp approximately 20 cm H2O) caused a backward traveling pressure wave of high amplitude, appearing in counter-phase to the forward pressure wave at the input site. The total pressure wave amplitude was thereby markedly lowered, resulting in a reduced Wp level. We assume that this effect of moderate vasoconstriction may be one reason for the existence of vascular smooth muscles in the pulmonary arteries.

Reduction of pulsatile hydraulic power in the pulmonary circultation caused by moderate vasoconstriction

Vascular input impedance and associated hydraulic power was measured in rabbit isolated lungs. The study was focused on changes in impedance and in pulsatile hydraulic power during relaxation and contraction of vascular smooth muscle. Pulsatile power was found to be at a minimum when smooth muscle tone was such that the pulmonary arterial pressure was in the physiological range, and increased both when the vessels were relaxed and further constricted. Input impedance was found to be determined mainly by the large, proximal ('extra-alveolar') arteries.

The pulmonary vasoconstrictor response to hypoxia: effects of inhibitors of prostaglandin biosynthesis

The main purpose of the present work was to determine whether prostaglandins (PGs) synthetised in the lungs mediate the vasoconstrictor response to acute alveolar hypoxia. Isolated and ventilated lungs of rats were perfused at 37 degrees C with homologous blood at constant-volume, pulsatile inflow, and pressor responses to 3 min periods of standardized ventilation hypoxia recorded. Indomethacin, sodium meclofenamate and acetylsalicylic acid (all 100 mug/ml), which are potent inhibitors of PG biosynthesis, did not reduce the hypoxic vasoconstrictor response. Sometimes they even enhanced this response. We conclude that PGs do not mediate the hypoxia-induced vasoconstriction. We suggest that vasodilatory PGs might act to reduce and modify pulmonary arterial hypertension due to hypoxia.

Interrelations between pulmonary liquid volumes and lung compliance

We have investigated the relative effects of lung edema and of increases in pulmonary blood volume (PBV) on lung compliance (CL), and also the effects of selective elevations of pulmonary arterial (Ppa) and left atrial (Pla) pressures on PBV and on CL, using an isolated, perfused, and ventilated rabbit lung preparation. Lung weight was continuously recorded. A step rise in Pla at constant flow caused a rapid rise in PBV accompanied by an immediate fall in CL. With maintained high vascular pressures interstitial edema accumulated with no further fall in CL. Not until 3 times the normal amount of extra-vascular fluid had accumulated did a further, secondary reduction in CL occur. When Ppa was elevated to the same level by 1) a rise in flow and 2) a rise in Pla, the latter type of experiment gave 3-5 times larger increases in PBV. Pla elevations with or without rise in Ppa (flow adjusted) gave almost the same rises in PBV. The fall in CL was related to rises in PBV regardless of how such rises were obtained. Our conclusion is that increases in PBV, but not accumulation of interstitial edema, reduced CL in this preparation.