bluuebunny/crossref_metadata_2025_split huggingface dataset:
Potassium activated phosphatase from human red blood cells. The mechanism of potassium activation
Authors: Garrahan P. J. , Pouchan María I. , Rega A. F. 
Published: December 2014

1. The kinetic behaviour of the K‐activated phosphatase in human red blood cell membranes has been investigated. The concentration of Mg required to give optimal activation is independent of substrate and K concentration, suggesting that Mg combines with the enzyme at a site that is independent of and non‐interacting with the substrate and K sites.2. The effects of K are competitively antagonized by Na. Ouabain in suitable concentrations selectively abolishes the activating effect of K.3. Comparison between the hydrolysis of acetylphosphate by intact red cells and by fragmented ghosts suggests that the active site for the substrate is only accessible at the internal surface of the cell membrane.4. The plot of the total rate of p‐nitrophenylphosphate hydrolysis versus substrate concentration can be fitted at any K concentration by a rectangular hyperbola. The effect on the total rate of increasing K concentration is exerted mainly on the apparent affinity for the substrate, which increases about 5 times as K goes from 0 to 55 m
M. There is also a much smaller increase in the maximum velocity (about 1·3 times) for the same range of K concentrations.5. If the difference between the activity in the absence and in the presence of K is plotted as a function of substrate concentration, the curves obtained are no longer hyperbolic but pass through a maximum and then tend to a lower value.6. This kinetic behaviour can be explained much more easily by assuming that a single enzyme is responsible for the hydrolysis of the substrate in the presence and in the absence of K. A simple kinetic model based on this assumption was developed and when experimentally determined constants were fitted into the equations that predict its behaviour a reasonably good agreement between theory and experiment was obtained.7. In the ‘single enzyme’ model inhibitors that selectively abolish the K‐dependent activity would act by blocking the combination of the enzyme with K. A simple treatment based on this idea was developed for the case of Na and its predictions were fulfilled by the experimental results.8. In the ‘single enzyme’ model the K‐coupled hydrolysis is always larger than the difference between the rates in the presence and in the absence of K, and when K concentration is non‐limiting the K‐coupled rate is equal to the total rate.
Factors affecting mucosal water and sodium transfer in everted sacs of rat jejunum
Authors: Crocker Ann D. , Munday Kenneth A. 
Published: December 2014

1. Mucosal water and sodium transfer were measured in everted sacs of rat jejunum.2. There was no effect on mucosal water and sodium transfer when aldosterone was added to the incubation medium.3. An 87% increase in mucosal water and sodium transfer was obtained in sacs prepared from animals maintained on a low sodium diet compared to sacs from animals on a normal diet.4. Injection of 5 μg aldosterone intraperitoneally to animals maintained on a high sodium diet produced a significant increase in mucosal water and sodium transfer in sacs prepared 27 hr later and this was still present 36 hr after injection.5. The aldosterone‐induced rise in mucosal water transfer was blocked if actinomycin D was administered one hour before the aldosterone injection.6. It is suggested that aldosterone action on sodium and water transport in rat jejunum is mediated through a primary action on protein synthesis and that the long delay can be explained in terms of gut morphology.
The variations in visual threshold measurement
Authors: Hallett P. E. 
Published: December 2014

1. This paper presents a statistical analysis of the thresholds of test flashes viewed against zero, steady or transient backgrounds by peripheral vision. The method of threshold measurement is that of the Medical Research Council Report (Pirenne, Marriott & O'Doherty, 1957; Hartline & McDonald, 1943). The data are from the previous paper (Hallett, 1969b) and consist of k days’ samples of n threshold measurements on an intensity scale of interval 0·087 log. The collection of a sample required 5‐6 min and the samples were spread over a 3‐month period.2. The analysis suggests that the nature of biological variations is that the ‘instantaneous’ frequency‐of‐seeing curve can occupy a variety of positions, or levels, scattered about its typical position on the log. energy axis. Change of the position of the curve for a given threshold task is most obvious when one compares threshold measurements obtained on different days, but this is not true day‐to‐day variation; the same sorts of change occur on the same day if the viewing conditions (independent variables) are changed and are perhaps due to shifts in the observer's signal/noise criterion K.3. Two important consequences of the analysis are (i) the errors of visual threshold functions are worse than one method of calculating error suggests and (ii) it is possible to eliminate part of the biological variations from a particular sort of frequency‐of‐seeing curve and thus obtain a better estimate of the instantaneous curve which is the physiological function of prime interest.4. Some possible causes of the biological variations are considered. The design of experiments is discussed. The method of the M.R.C. Report is to be recommended since it can be applied without prior assumptions about the value of the mean threshold or the nature of the errors.
Stimulation of adrenal glucocorticoid secretion in man by raising the body temperature
Authors: Collins K. J. , Few J. D. , Forward T. J. , Giec L. A. 
Published: December 2014

1. Plasma cortisol and corticosterone concentrations increased significantly in eleven resting, unacclimatized subjects after 2 hr exposure to an ambient temperature of 46° C dry bulb, 36° C wet bulb and in two subjects investigated by controlled elevation of body temperature in a hyperthermia test‐bed.2. In the same experiments the urinary excretion of 17‐hydroxycorticosteroids (17‐OHCS) estimated as the 11‐oxy and 11‐deoxy fractions did not differ significantly in hot and in control conditions.3. Following an initial fall in plasma cortisol concentration during the first hour of heat exposure, cortisol levels increased in the second hour when body temperatures exceeded a ‘critical’ level of 38·3° C. Two acclimatized subjects did not attain this body temperature even after 2 hr heating and showed no increase in plasma glucocorticoid levels.4. Sweat collected in arm bags, or by suction, in controlled hyperthermia experiments contained negligible amounts of cortisol (0·34–1·70 μg/100 ml. sweat).5. Changes in plasma cortisol specific activity after intravenous injection of 1,2[3H]cortisol indicated that the raised plasma concentration was brought about by increased adrenal secretion, though this was accompanied by more rapid removal of cortisol from the circulation in hot conditions. Excretion of tritium by the kidney was not significantly altered. It was not possible to determine whether changes in liver function contributed to the elevation of the plasma cortisol level but it was found that a larger proportion of cortisol was oxidized to cortisone, or to a metabolite closely resembling cortisone, in the heat.
Some effects on the blood vessels of the human forearm of local exposure to pressures below atmospheric
Authors: Ardill B. L. , Fentem P. H. , Finlay R. D. , Isaac P. 
Published: December 2014

1. Measurements were made of the initial rate of change of volume of the forearm when the limb was suddenly exposed to various pressures below atmospheric; this was taken to indicate the arterial inflow under these conditions.2. The relationship between arterial inflow and the change in external pressure was curvilinear, with the convexity towards the pressure axis. At −90 mm Hg inflow was increased more than fivefold.3. With short repeated exposures to negative pressure the inflow to the limb showed a progressive decrease for successive exposures until a steady value was obtained.4. The relationship between arterial inflow and the reduction of external pressure during short repeated periods of exposure (6th–10th exposures) was linear from ambient to −80 mm Hg.5. Measurements of forearm blood flow after one, four and ten exposures to reduced external pressure showed that vasoconstriction developed within 20 sec of the end of the exposure and took about 60 sec to disappear. There were only slight differences in the degree of vasoconstriction induced by the different numbers of exposures.
The inhibitory effect of convulsant agents on the enzyme in brain which inactivates nerveside
Authors: Toh C. C. 
Published: December 2014

1. An enzyme which can be extracted from brain inactivates nerveside in the optimum pH range 5·8–7·0.2. The polybasic acids trypan blue and its analogue trypan red, bromphenol blue and its analogue bromthymol blue at concentrations of 0·22 m
M and ethylenediaminetetra‐acetic acid (EDTA) at a concentration of 1 m
M are strong inhibitors of the enzyme.3. Penicillin which is a monobasic carboxylic acid also inhibits the enzyme but only if concentrations as high as 3·6 m
M are used. The antibiotic streptomycin which is a basic substance does not inhibit the enzyme.4. Caffeine at a concentration of 7·2 m
M only weakly inhibits the enzyme.5. Chymotrypsin and wheat germ acid phosphatase also inactivate nerveside at pH 5·9 and are inhibited by the acidic dyes and penicillin. EDTA inhibits wheat germ phosphatase but activates chymotrypsin.6. Inactivation of nerveside by the brain enzyme and by wheat germ phosphatase is different from the action of chymotrypsin. Nerveside solutions incubated with chymotrypsin completely lose all biological activity whereas if incubation is carried out with either the brain enzyme or wheat germ acid phosphatase a residual biological activity remains even when the concentration of these two enzymes is increased. This residual biological activity is due to a peptide as it is destroyed by chymotrypsin.7. The manner in which nerveside is inactivated by the brain enzyme is uncertain as the preparation of the latter contained phosphodiesterase and protease activities which were similarly inhibited by the acid dyes, penicillin and EDTA.8. Pentylenetetrazole, picrotoxin, strychnine and tetanus toxin do not inhibit the brain enzyme.9. The nerveside‐inactivating enzyme is not identical with the Substance P‐inactivating enzyme in brain as the former is inhibited by EDTA while the latter is not.
The effect of hypothalamic lesions on the melanocyte‐stimulating hormone content and histology of the pars intermedia of the rat pituitary gland
Authors: Howe A. , Thody A. J. 
Published: December 2014

1. The effect of bilateral lesions in the anterior hypothalamus on the histology and content of melanocyte‐stimulating hormone (MSH) of the pars intermedia has been studied in the adult male rat.2. By 7–15 days striking histological changes, suggestive of hyperactivity, were evident. These changes were accompanied by an elevated MSH content, which was particularly noticeable at 7 days.3. By 7 days there was an increase in the acid phosphatase activity of pars intermedia cells, as demonstrated histochemically.4. It was concluded that a hypothalamic control system exists for the mammalian pars intermedia and may involve both inhibitory and excitatory components.
The effect of topically applied atropine on resting and evoked cortical acetylcholine release
Authors: Dudar J. D. , Szerb J. C. 
Published: December 2014

1. Cortical acetylcholine (ACh) output was measured in cats anaesthetized either with Dial compound (0·6 ml./kg) or with halothane—N2O. ACh output was found to be 1·67 ng/cm2.min under Dial anaesthesia, and 0·30 ng/cm2.min under halothane—N2O.2. Addition of atropine sulphate (1 μg/ml.) to the collection fluid increased ACh output fourfold under Dial anaesthesia but had no effect under halothane—N2O anaesthesia.3. Isolation of the cortex, lesions in the mesencephalon and topical application of tetrodotoxin (TTX) reduced ACh output under Dial anaesthesia to about 0·8 ng/cm2.min. The effect of atropine on ACh output was somewhat reduced by isolation and completely abolished by mesencephalic lesions or TTX.4. ACh release evoked by reticular formation stimulation under halothane—N2O anaesthesia was increased fourfold by atropine but evoked release due to direct stimulation of the cortex was increased only twofold.5. ACh release due to depolarization of the cortex with KCl was not increased by atropine.6. Dihydro‐β‐erythroidine (DHE) or
D‐tubocurarine failed to affect ACh output even in a concentration of 100 μg/ml.7. It is concluded that atropine does not increase spontaneous ACh release and only ACh release evoked by trans‐synaptic stimulation of cholinergic neurones is potentiated by atropine.8. These findings are fully consistent with the hypothesis that atropine increases ACh output by blocking cortical cholinergic synapses which are a part of a circuit inhibiting cholinergic neurones.
Circulatory changes and renin secretion in sheep in response to feeding
Authors: Blair-West J. R. , Brook A. H. 
Published: December 2014

1. The effect of feeding on the circulation, on renin release and on renal function has been examined in the sheep.2. There was a rapid reduction of plasma volume within 15 min of starting to eat dry feed.3. This was accompanied by an abrupt rise in systolic blood pressure and by a more gradual and prolonged elevation of heart rate.4. Within 30 min of feeding there occurred renal conservation of sodium and water which continued for at least 2‐3 hr.5. Renin was released into the circulation of sheep that ate rapidly; slow feeders did not show this response.6. The rise in plasma renin concentration was inhibited by infusing a solution similar in composition to mixed saliva at a rate that prevented the change in plasma volume.7. It is concluded that the rapid transfer of sodium and water from the circulation to the rumen via the saliva during ingestion of dry feed is sufficient to activate the renin/angiotensin system.
The effects of alloxan and histamine on the permeability of the pulmonary alveolocapillary barrier to albumin
Authors: Goetzman Boyd W. , Visscher Maurice B. 
Published: December 2014

1. [131I]albumin transport from alveolus to perfusion fluid was evaluated in an isolated dog lung lobe preparation perfused at constant pressure with homologous plasma. The alveoli were filled with a 1:1 mixture of Ringer—Tyrode solution and plasma.2. For twenty‐three lung lobes, an average control permeability coefficient of the alveolocapillary membrane for albumin was found to be 1·9 × 10−9 cm/sec with a range of (0·3–5·5) × 10−9 cm/sec.3. Alloxan in concentrations of 0·22–2·50 mg/ml. perfusate was observed to increase the alveolocapillary membrane permeability to [131I]albumin with a positive correlation between dose and effect. The larger doses of alloxan increased the permeability by a factor of ten or more.4. Glutathione (GSH), administered intravascularly 2 min before alloxan in an 8:1 molar ratio of GSH:alloxan, delayed the onset of the permeability increase due to alloxan by 40–60 min but did not influence the maximum increase in permeability.5. Histamine administered intravascularly in concentrations from 0·02 to 0·50 μg/ml. perfusate had no significant effect on the alveolocapillary membrane permeability to [131I]albumin.
The kinetics of mechanical activation in frog muscle
Authors: Adrian R. H. , Chandler W. K. , Hodgkin A. L. 
Published: December 2014

1. The kinetics of mechanical activation were examined in muscle fibres of the frog's sartorius muscle, using a voltage clamp to control membrane potential, tetrodotoxin to eliminate electrical activity and microscopic observations to determine the mechanical threshold.2. The strength—duration curve was determined over a range of membrane potentials varying between −52 mV (rheobase) and +90 mV. At 4° C the critical duration was about 11 msec at −30 mV, 4 msec at 0 mV and 2 msec at +40 mV.3. For pulses where V > −10 mV the threshold criterion at 4° C was that the ‘area above −30 mV’ must exceed about 120 mV msec.4. The effect of a brief subthreshold pulse declines with a time constant of about 3 msec at −100 mV and about 8 msec at −85 mV at 4° C.5. Although the strength—duration curve is well fitted by assuming a first‐order mechanism in which the rate of release of activator increases with membrane potential, other experiments show that the over‐all mechanism is probably second order in time.6. A short pulse must be at least 50% threshold if it is to give a visible contraction when added to a long pulse which is just below rheobase.7. Delayed rectification was conspicuous with medium or long pulses which were just below the mechanical threshold, but short pulses could give contraction without turning on any appreciable potassium conductance.8. The Appendix extends Falk's (1968) treatment of the charging of the tubular system under a voltage clamp.
Renal excretion of urea and electrolytes in sheep and red deer
Authors: Maloiy G. M. O. , Scott D. 
Published: December 2014

1. The effects of varying the intake of water and nitrogen on the renal excretion of urea and electrolytes has been studied in sheep and in red deer.2. The concentration of urea in the urine of both sheep and deer decreased as the volume of urine increased and about eight times as much urea was excreted each day when a high‐nitrogen diet was fed compared to when a low‐nitrogen diet was fed.3. Both the concentrations of sodium and potassium in the urine decreased as the urine volume increased but the total amounts excreted were independent of urine volume.4. The osmotic concentration of the urine decreased as urine volume increased.5. In both deer and sheep the concentration of urea in the plasma was considerably higher when a high‐nitrogen diet was fed compared to when a low‐nitrogen diet was fed but the rate of clearance of inulin from the plasma did not appear to be related to the diet.6. Appreciably more urea was filtered at the glomerulus when a high‐nitrogen diet was fed compared to when a low‐nitrogen diet was fed but the percentage of filtered urea reabsorbed was not related to diet.7. The results indicate no qualitative differences between deer and sheep in the renal excretion of urea and electrolytes.
The effect of acute changes in haematocrit in the anaesthetized dog on the volume and character of the urine
Authors: Nashat F. S. , Scholefield F. R. , Tappin J. W. , Wilcox C. S. 
Published: December 2014

1. Acute changes in haematocrit were produced by exchange transfusion of dextran‐in‐saline or packed red cells.2. There were no significant changes in glomerular filtration rate, blood pressure, central venous pressure, heart rate, respiratory rate, blood volume or extracellular fluid volume following the exchange transfusions.3. Urine volume increased after haemodilution but decreased after haemoconcentration.4. The diuresis after haemodilution occurred despite an infusion of ADH or alcohol. Thus it could not be attributed to a change in circulating ADH level.5. There were two types of diuresis. The ‘water diuretic’ response was characterized by an increase in free water clearance with a reduction in urinary sodium concentration; the ‘sodium diuretic’ response by an increase in urinary sodium concentration but no change, or a fall, in free water clearance.6. The results were related to changes in medullary osmotic gradient found by other workers to occur when medullary blood flow rate is altered.
The oxygen uptake and pulmonary blood flow during resuscitation from asphyxia in foetal and adult sheep
Authors: Bolton D. P. G. , Cross K. W. , Eitzman D. V. , Kelly J. 
Published: December 2014

1. The foetuses of twenty‐seven Welsh ewes and eight Clun Forest ewes were delivered by Caesarian section at an approximate gestational age of 140 days, maintaining the umbilical circulation. They were asphyxiated by clamping the umbilical cord, and resuscitated with IPPV. Oxygen consumption, heart rate, and blood pressures were recorded, and in one series of eight, blood flow through the left lung was recorded whilst IPPV was applied to this lung only.2. The hypothesis that oxygen consumption is abnormally low during resuscitation of the new‐born from extreme asphyxia because of limited blood flow, was supported.3. Adult ewes were also asphyxiated and in a series of eight a quite different pattern of behaviour was observed, due to very rapid and complete recovery of the circulation.4. Observations on the pulmonary vascular resistance suggest that complete vasomotor paralysis occurs during extreme asphyxia, so that resistance falls to a near‐minimum level for unexpanded lung. Expansion of the lung produced a large fall in resistance which appeared to be due to the introduction of gas into the alveolar spaces, lessening the resistance to flow of the capillaries.
Cerebral and cardiac enzymic activity and tolerance to asphyxia during maturation in the rabbit
Authors: Heidger Paul M. , Miller Faith S. , Miller James A. 
Published: December 2014

The tolerance of neonatal rabbits to asphyxiation in 95% N2 + 5% CO2 was studied under conditions of controlled body temperature, and the enzymic activities of succinoxidase and lactic dehydrogenase were quantitatively determined in the heart and brain of untreated litter‐mates.1. In new‐born rabbits tolerance to asphyxia increases progressively as body temperatures are reduced until at 15° C it is four times that at 39° C. At colonic temperatures below 15° C, tolerance to asphyxia decreases rapidly.2. All new‐born rabbits having colonic temperatures of 15° C recover spontaneously from asphyxia two to four times as long as that which is lethal for their warm litter‐mates. Recoveries from asphyxia five and six times as long occur in 80%.3. At 39° C colonic temperature, the tolerance of new‐born rabbits to asphyxia decreases over ninefold from birth to young adulthood.4. In all tissues studied succinoxidase activity increases during the post‐natal period. In the heart and frontal lobe, lactic dehydrogenase activity tends to parallel that of succinoxidase and is lower in the new‐born than one might expect in view of the tolerance to asphyxia at this time.5. In the medulla oblongata an increase in succinoxidase activity occurs without a parallel increase in lactic dehydrogenase activity. This may reflect an increased dependence on aerobic pathways during post‐natal development, with no parallel increase in the capacity for anaerobic glycolysis. Such changes may explain in part why the sensitivity of the medullary respiratory centre complex to oxygen lack is so much greater in the adult than in the new‐born.
Specificity of cone mechanisms in lateral interaction
Authors: McKee Suzanne P. , Westheimer Gerald 
Published: December 2014

1. The increment threshold for a brief, small probing light flash was used as an indicator of the state of adaptation of the human fovea. It shows that illumination of a zone up to 7 min of arc in diameter desensitizes the retina and that the additional illumination of a surrounding zone acts to counteract the desensitization.2. The red and green colour mechanisms were isolated by selecting light of appropriate wave‐lengths for the adaptation and the increment stimuli and it was demonstrated that the desensitizing and sensitizing adaptation zones exist within each mechanism.3. Using the constancy of the increment threshold for a brief, small probing flash as a null‐indicator for equivalence of annuli of various wave‐lengths to produce a given amount of sensitization, the action spectrum for the laterally interacting region was obtained for both the red and the green mechanisms.4. For the red mechanism, the surrounding sensitizing zone has the action spectrum also of the red mechanism. For the green mechanism the surrounding sensitizing zone has a green action spectrum.