bluuebunny/crossref_metadata_2025_split huggingface dataset:
Pancreatic α Cell Function in the Fetal Foal During Late Gestation
Authors: Fowden A. L. , Forhead A. J. , Bloomfield M. , Taylor P. M. , Silver M. 
Published: May 2004

SUMMARYPlasma glucagon concentrations were measured in chronically catheterized fetal ponies and their mothers between 260 days of gestation and term (≈ 335 days). Fetal α cell responses to arginine and variations in fetal glycaemia were also examined during late gestation. Immunoreactive glucagon was present in fetal plasma at 260 days of gestation and its concentration in utero increased after 320 days and then again at birth. Maternal plasma glucagon concentrations were higher after 300 days than earlier in gestation but were lower than the corresponding fetal value throughout the period of gestation studied. Fetal α cells responded rapidly to intravenous arginine infusion but not to changes in the fetal glucose level induced by maternal fasting for 36 h or by intrafetal infusion of glucose. The maximal increment in fetal plasma glucagon in response to arginine occurred at the end of the 5 min infusion and was positively correlated to the basal pre‐infusion plasma glucagon concentrations. Fetal plasma glucagon concentrations were unaffected by either hyper‐ or hypoglycaemia. In contrast, maternal plasma glucagon levels were significantly increased by fasting. These observations indicate that equine pancreatic α cells are functional in utero but that they are unresponsive to variations in glycaemia until after birth.
Laryngeal Movements During the Respiratory Cycle Measured with an Endoscopic Imaging Technique in the Conscious Horse at Rest
Authors: Lafortuna Claudio L. , Albertini Mariangela , Ferrucci Francesco , Zucca Enrica , Braghieri Martina , Clement M. Giovanna , Saibene Franco 
Published: May 2004

SUMMARYA video‐laryngoscopic method, implemented with an algorithm for the correction of the deformation inherent in the endoscope optical system, has been used to measure the dorsoventral diameter (Drg) and the cross‐sectional area (CSArg) of the rima glottidis in five healthy workhorses during conscious breathing at rest. Simultaneous recording of the respiratory airflow was also obtained in two horses. Drg measured 82·7 ± 4·5 mm (mean ±s.d.) independently of the respiratory phase, and did not differ from the measurement in post‐mortem anatomical specimens of the same horses. CSArg ranged from 1130 ± 117 mm2 (mean ±s.d.) during the inspiratory phase to 640 ± 242 mm2 during the expiratory phase, being always narrower than tracheal cross‐sectional area, which was 1616 ± 224 mm2, as determined from anatomical specimens. Both inspiratory and expiratory airflow waves displayed a biphasic pattern. Maximal laryngeal opening occurred in phase with the second inspiratory peak, while during expiration CSArg attained a minimum value during the first expiratory peak which was significantly smaller (P < 0·01) than the area subsequently maintained during the rest of the expiratiory phase. These quantitative measurements of equine laryngeal movements substantiate the important role played by the larynx in regulating upper airway respiratory resistance and the expiratory airflow pattern at rest.
Development of the Fluorescent Microsphere Technique for Quantifying Regional Blood Flow in Small Mammals
Authors: Deveci D. , Egginton S. 
Published: May 2004

SUMMARY

Tissues weighing from 0·006 to 3·0 g were dissected and put directly into 15 ml screw cap polypropylene tubes with a conical base (maximum of 3 g per tube). It proved unnecessary to mince tissue, even though smaller pieces may aid quicker digestion. Five millilitres of 2 M KOH in 99 % (IMS) ethanol with 0·5 % Tween‐80 was then added. Tissue digestion was usually completed in 2‐4 h using a dry heating block held at 60°C, with intermittent shaking. Samples were routinely processed using fresh tissues, although storage of frozen tissue (in the dark at ‐20°C) introduced no detectable error in BF estimation and tended to aid tissue maceration.
After digestion was completed the tubes were centrifuged at 3000 r.p.m. (1500 g) for 15 min.
The supernatant was carefully aspirated until < 500 μl was left, thereby reducing the possibility of accidental loss of microspheres.
After 1 ml dH2O was added the tubes were quickly vortexed to prevent microsphere flocculation and aid resuspension of remaining pellets, while the subsequent addition of ethanoic Tween (100 % ethanol + 0·5 % Tween‐80) allowed complete sedimentation by centrifugation.
Nine millilitres of ethanoic Tween‐80 was added, and the tubes were vortexed and spun at 1500 g for 15 min.
The supernatant was aspirated as above (Step 3).
Five millilitres of 100 mM phosphate buffer (pH 7·00) was added to neutralize the pellet as alkaline solutions quench fluorescence. Using aqueous solutions increased the possibility of microsphere loss by adhesion to the surface of tubes or aggregation, which could readily be seen by eye when tubes were examined under bright light, and hence the buffer was followed by addition of 4 ml absolute ethanol and further vortexing, before spinning (1500 g) for 20 min.
The supernatant was aspirated, leaving up to 300 μl depending on the amount of tissue residue, and the remaining microspheres and pellet were quickly vortexed to ensure complete resuspension.
The tubes were left to evaporate in an oven at 60°C and then briefly vortexed during this period to disperse more of the flocculent, until around 100 μl fluid remained. This improves solvent extraction of microspheres, which may be less efficient in a completely dry pellet.
Two or three millilitres of solvent (di(ethylene glycol) ethyl ether acetate, 98 %; Aldrich Chemical Co., Poole, Dorset, UK) was added according to the expected fluorescence intensity, and vortexed several times over 3‐5 min. After 30 min the tubes were sonicated in a water bath for 5 min to complete dye extraction by the solvent. The tubes were kept as far as possible in the dark after the solvent was added to avoid photo‐bleaching of the fluorescent dyes.
After sonication, the tubes were occasionally spun (1500 g) once more to sediment any undigested/undissolved material, though this was rarely necessary in our experiments. Readings should be completed within 1 h to avoid loss of signal intensity.
Role of Nitric Oxide Synthase and Cyclooxygenase in Pulmonary Vascular Control in Isolated Perfused Lungs of Ferrets, Rats and Rabbits
Authors: Liu Xia , Bee Denise , Barer Gwenda R. 
Published: May 2004

SUMMARYDilator products of nitric oxide synthase (NOS) and cyclooxygenase (COX) may contribute to the low normal pulmonary artery pressure (Ppa). In isolated perfused lungs of ferrets, rabbits and rats we investigated this hypothesis by blockade of NOS with L‐NAME (L‐nitro‐arginine methyl ester) and COX with meclofenamate. There were species differences. Inhibition of either enzyme caused little rise in Ppa in ferrets and rats but inhibition of both enzymes caused huge increases in Ppa. We suggest this might be due to intracellular connections between the excitatory pathways for NOS and COX dilators, such that inhibition of one enzyme leads to activation of the other. Impairment of these endothelial‐based enzymes in pulmonary vascular disease might lead to severe pulmonary hypertension. By contrast, in rabbits, comparable doses of L‐NAME lead to large rises in Ppa which were reversed rather than amplified by COX blockade. NO seems to protect against some pressor/oedema forming product of COX in this species.
Inhibition of Mucosal Glycylsarcosine Uptake by Acetate in Rat Distal Small Intestine
Authors: Scharrer E. , Amstutz I. , Grenacher B. 
Published: May 2004

SUMMARYAcetate deriving from microbial fermentation may occur at considerable concentrations in the distal small intestine, where it appears to be absorbed by two different mechanisms: acetate‐HCO3− exchange and non‐ionic diffusion. Whether acetate affects absorption of other nutrients at this intestinal site is not known. Therefore the influence of acetate (30 mmol l−1) on oligopeptide absorption was studied using an in vitro mucosal uptake technique allowing measurement of substrate uptake across the brush border membrane (BBM). Acetate significantly inhibited mucosal uptake of 14C‐labelled glycylsarcosine (Gly‐Sar) at pH 6 and pH 7 in the presence of sodium. No inhibition occurred in the absence of sodium. Both acetate and the absence of sodium decreased Vmax of mucosal Gly‐Sar uptake without substantially affecting the apparent Km value. Since it is well established that Vmax of peptide transport across the intestinal BBM depends on the size of the transmembrane H+ gradient as a driving force the present findings are in accordance with the assumption that acetate inhibits peptide absorption by attenuating the H+ gradient across the BBM, which depends on the presence of sodium.
Non‐Muscarinic and Non‐Nicotinic Inhibition by the Acetylcholine Analogue Carbachol of the Delayed Rectifier Potassium Current, ik, in Rabbit Isolated Sino‐Atrial Node Cells
Authors: Lei Ming , Kohl Peter , Brown Hilary , Noble Denis 
Published: May 2004

SUMMARYThe effect of carbachol, an analogue of acetylcholine, on the delayed rectifier potassium current, iK, was investigated in rabbit isolated sino‐atrial node cells using the whole cell patch clamp technique with amphotericin‐permeabilized patches. In the presence of 500 nM atropine and 500 nM hexamethonium to block muscarinic and nicotinic receptors, respectively, 500 nM carbachol decreased the amplitude and rate of deactivation of iK without, however, affecting the slope of the iK activation curve. The same concentration of carbachol decreased the pacemaking rate of spontaneously active sino‐atrial node cells by more than 13%. Thus, there is a non‐muscarinic and non‐nicotinic pathway for cholinergically induced reduction in the amplitude and rate of deactivation of iK that would appear to contribute to negative chronotropy in rabbit sino‐atrial node pacemaker cells.
Influence of Thyrotrophin‐Releasing Hormone on Thermoregulatory Adaptation after Birth in Near‐Term Lambs Delivered by Caesarean Section
Authors: Heasman Lindsay , Clarke Lynne , Symonds Michael E. 
Published: May 2004

SUMMARYWe investigated the hypothesis that exogenous stimulation with thyrotrophin‐releasing hormone (TRH) immediately prior to umbilical cord clamping can improve thermoregulatory adaptation after birth in near‐term lambs delivered by Caesarean section. Lambs received an umbilical vein injection of saline ± TRH (8 μg) prior to cord clamping. The rate of change in colonic temperature and oxygen consumption after birth were not influenced by TRH, but TRH‐treated lambs exhibited a greater incidence of shivering compared with controls over the first hour of neonatal life. Two and a half hours after birth, TRH‐treated lambs possessed brown adipose tissue (BAT) with a higher thermogenic activity (i.e. GDP binding to mitochondrial protein), but their BAT had a reduced DNA content and they had less hepatic glycogen than control lambs. TRH administration had no effect on iodothyronine 5′ deiodinase activity in BAT and liver, or on plasma concentrations of total triiodothyronine, thyroxine, cortisol or free fatty acids. Three TRH‐treated but no control lambs, failed to establish continuous breathing, so tissues from these treated lambs together with time‐matched controls were sampled 25 min after birth. These ‘non‐surviving’ TRH‐treated lambs had very high plasma catecholamine concentrations, but their lung weights were similar to controls. ‘Surviving’ TRH‐treated lambs possessed lungs with less DNA than non‐surviving TRH‐treated lambs. It is concluded that umbilical vein injection of TRH prior to umbilical cord clamping increases the recruitment of both shivering and non‐shivering thermogenesis after birth.
Measurement of Changes in Glomerular Filtration Rate Induced by Atrial Natriuretic Peptide in the Rat Kidney
Authors: Caron N. , Kramp R. 
Published: May 2004

SUMMARYThis study was undertaken to improve the measurement of glomerular filtration rate (GFR) during the acute diuretic phase induced by atrial natriuretic peptide (ANP), which may indeed alter the renal clearance of inulin (GFRCL) due to dead space error. A technique to measure GFR without urine collections was therefore developed in anaesthetized rats prepared as for micropuncture. To do so, arterial blood was periodically collected and renal venous blood was withdrawn simultaneously from a catheter inserted into the left suprarenal vein to determine the renal extraction coefficient of inulin (CEIN). In addition, renal blood flow (RBF) was continuously measured with an electromagnetic flow transducer fitted around the left renal artery to estimate renal plasma flow (RPF). GFR (GFRCE) was then calculated as the product of RPF and CEIN. To study the effects of ANP on GFR, rats were injected i.v. with 10 μl of saline without (n= 6; vehicle) or with 1 μg ANP (n= 6; ANP) and GFRCE and GFRCL were compared before and after each treatment. They did not differ significantly during baseline measurements in each experimental group and were not modified after vehicle. Similarly, RBF remained constant. In contrast, RBF and GFRCE increased rapidly and simultaneously 90 s after ANP, from 9·07 ± 0·25 to 10·07 ± 0·35 (12%) and from 1·209 ± 0·188 to 1·715 ± 0·190 ml min−1 (42%), respectively (P < 0·05). GFRCL increased to an even greater extent (88%). Moreover, the peak enhancement of GFRCL was delayed and occurred 180 s after ANP. The renal clearance of inulin was thus unduly elevated due to sudden changes in the dead space induced by the diuretic effect of ANP. In conclusion, determination of glomerular filtration rate by the method of renal extraction of inulin provided more reliable results than those achieved using the classical method of renal clearance of inulin. Moreover, it was sufficiently sensitive to detect small and transient changes in GFR induced by the injection of 1 μg ANP.
Chemoattractant‐ and Mitogen‐Induced Generation of Reactive Oxygen Species in Human Lymphocytes: The Role of Calcium
Authors: Orie Nelson N. , Zidek Walter , Tepel Martin 
Published: May 2004

SUMMARYThis study examined the role of calcium in the generation of reactive oxygen species (ROS) in human lymphocytes activated by the chemoattractant formyl‐Met‐Leu‐Phe (fMLP) and the T‐cell mitogen phytohaemagglutinin (PHA). The concentrations of cytosolic calcium ([Ca2+]i) and ROS were monitored simultaneously with a fluorescence spectrophotometer after the cells had been incubated in fura‐2 (calcium‐sensitive dye) and 2′,7′‐dichlorofluorescein diacetate (DCF‐DA, ROS‐sensitive dye). The lymphocytes were stimulated with fMLP (200 nmol l−1) or PHA (10 μmol l−1) in the absence and presence of extracellular calcium. A dose‐response test was also conducted for extracellular calcium. fMLP and PHA significantly increased both [Ca2+]i (P < 0.001) and ROS concentrations (P < 0.001) above the control levels in the presence of extracellular calcium. However, such increases were abolished in the absence of extracellular calcium, suggesting total dependence of the responses to both fMLP and PHA on transplasma‐membrane calcium influx. There were also graded increases in ROS with increasing concentrations of extracellular calcium. The results show that transplasma‐membrane calcium influx is essential for fMLP‐ and PHA‐induced generation of reactive oxygen species in human lymphocytes.
Oxygen Uptake Kinetics of Older Humans are Slowed with Age but are Unaffected by Hyperoxia
Authors: Bell C. , Paterson D. H. , Kowalchuk J. M. , Cunningham D. A. 
Published: May 2004

SUMMARYCross‐sectional studies have compared the oxygen uptake (VO2) kinetics during the on‐transient of moderate intensity exercise in older and younger adults. The slower values in the older adults may have been due to an age‐related reduction in the capacity for O2 transport or alternatively a reduced intramuscular oxidative capacity. We studied: (1) the effects of ageing on VO2 kinetics in older adults on two occasions 9 years apart, and (2) the effect of hyperoxia on VO2 kinetics at the second test time. After a 9 year period, follow‐up testing was undertaken on seven older adults (78 ± 5 years, mean ±s.d.). They each performed six repeats of 6 min bouts of constant‐load cycle exercise from loadless cycling to 80 % of their ventilatory threshold. They breathed one of two gas mixtures (euoxia: inspired O2 fraction, FI,O2, 0·21; hyperoxia: FI,O2, 0·70) on different trials determined on a random basis. Breath‐by‐breath VO2 data were time aligned and ensemble averaged. VO2 kinetics, modelled with a single exponential from phase 2 onset (+20 s) to steady state and described by the exponential time constant ([tau]) were compared with data collected from the same adults 9 years earlier. One‐way repeated measures analysis of variance revealed that [tau] was slowed significantly with age (from 30 ± 8 to 46 ± 10 s), but was unaffected by hyperoxia (43 ± 15 s). We concluded that: (1) in older adults studied longitudinally over a 9 year period, the on‐transient VO2 kinetics are slowed, in agreement with, but to a greater extent, than from cross‐sectional data; and (2) the phase 2 time constant ([tau]) for these older adults was not accelerated by hyperoxic breathing. Thus the expected hyperoxia‐induced increase in the capacity for O2 transport was not associated with faster on‐transient VO2 kinetics suggesting either that O2 transport may not limit VO2 kinetics during the 8th decade, or that O2 transport was not improved with hyperoxia.
Effects of Changes in pH and PCO2 on Wall Tension in Isolated Rat Intrapulmonary Arteries
Authors: Sweeney Michele , O'Regan Ronan G. , McLoughlin Paul 
Published: May 2004

SUMMARYWe examined mean (±s.e.m.) changes in wall tension in isolated rat intrapulmonary arteries on switching from control conditions (pH 7.38 ± 0.01; PCO2, 34.4 ± 0.5 mmHg) to hypercapnic acidosis (pH change, ‐0.24 ± 0.01; PCO2 change, +27.5 ± 0.9 mmHg), isohydric hypercapnia (pH change, ‐0.02 ± 0.01; PCO2 change, +28.5 ± 0.8 mmHg) and normocapnic acidosis (pH change, ‐0.24 ± 0.01; PCO2 change, ‐0.5 ± 0.3). Arteries were submaximally preconstricted with prostaglandin F2alpha; and changes in tension are expressed as a percentage of the 80 mM KCl‐induced contraction (%Po). Mean changes in wall tension on switching to hypercapnic acidosis (+4.4 ± 3.7%Po), isohydric hypercapnia (+1.9 ± 2.2%Po) and normocapnic acidosis (−1.5 ± 1.9%Po) were not significantly different from the change observed on switching to control conditions (+3.5 ± 1.1%Po), and were unaltered by endothelial removal. In isolated carotid preparations, the change in tension in isohydric hypercapnia (‐6.8 ± 7.1%Po) was not significantly different from that observed in control switches (+8.6 ± 3.2%Po). Significant reductions in tension (P < 0.001) were observed in hypercapnic (‐42.9 ± 7.8%Po) and normocapnic acidosis (‐36.4 ± 9.0%Po). These data suggest that intrapulmonary arteries are resistant to the vasodilator effects of extracellular acidosis observed in systemic (carotid) vessels.
Effect of Altered Body CO2 Stores on Pulmonary Gas Exchange Dynamics During Incremental Exercise in Humans
Authors: Ozcelik O. , Ward S. A. , Whipp B. J. 
Published: May 2004

SUMMARYThe lactate threshold is a widely used and, at times, controversial construct in exercise physiology and pathophysiology. Its non‐invasive estimation during incremental exercise depends upon CO2 output increasing as a function of O2 uptake, i.e. ‘V‐slope’, as a result of bicarbonate buffering during the lactic acidosis. However, we hypothesised that the V‐slope deflection could also occur as a consequence of metabolic CO2 being diverted proportionally more into the CO2 stores in the early phase of exercise. Eight healthy males performed two incremental exercise tests on a cycle ergometer, with and without controlled prior hyperventilation; the hyperventilation caused end‐tidal PCO2 to decline by [sim]10 mmHg, with the clearance of a CO2 volume averaging 2547 ml. This corresponded to an ‘effective’ CO2 capacitance of some 3·12 ml mmHg−1 kg−1. Gas exchange was determined breath‐by‐breath, and blood was sampled from the dorsum of the heated hand. Our results demonstrate that the early dynamics of CO2 wash‐in to the previously depleted body stores can result in a ‘pseudo‐threshold’, i.e. significantly before the onset of the actual lactic acidosis. Precautions should therefore be taken to avoid hyperventilation prior to non‐invasive estimation of the lactate threshold.
Pyrimidine Nucleotide‐Evoked Inhibition of Cyclic AMP Accumulation in Equine Epithelial Cells
Authors: Wilson Stuart M. , Gallagher Marie , Rakhit Soma , Remsbury Anna L. , Ko Wing Hung 
Published: May 2004

SUMMARYUridine triphosphate (UTP) evoked inhibition of adrenaline‐evoked cAMP accumulation in cultured equine epithelial cells (EC50, 1·8 ± 0·2 μM) and this effect was mimicked by 5‐Br‐UTP (EC50, 6·6 ± 1·8 μM) and uridine diphosphate (UDP; EC50, 96 ± 26 μM). This inhibitory action of UTP was abolished by pre‐treating cells with pertussis toxin (10 ng ml−1, 24 h). UTP (EC50, 2·3 ± 0·3 μM) and 5‐Br‐UTP (EC50, 29·4 ± 9·4 μM) also increased intracellular free calcium ([Ca2+]i) whilst UDP did not; the two effects are thus differentially sensitive to these pyrimidine nucleotides. ATP evoked cAMP accumulation in control cells and this response was unaffected by pertussis toxin. There is, therefore, no indication that ATP activates the pertussis toxin‐sensitive inhibitory pathway. The UTP‐evoked inhibition of cAMP accumulation was abolished by isobutylmethylxanthine (IBMX, 5 mM) and so the negative control over cAMP levels appears to be mediated by receptors that are selectively activated by pyrimidine nucleotides and permit control over phosphodiesterase activity.
Mechanical Properties of Smooth Muscle Portal Vein in Normal and Dystrophin‐Deficient (MDX) Mice
Authors: Mancinelli R. , Tonali P. , Romani R. , Tringali A. , Vargiu R. , Azzena G. B. 
Published: May 2004

SUMMARYMechanical properties of the vascular smooth muscle from normal and dystrophin‐deficient (mdx) mice were examined. Changes in resting and developed tensions in response to stretch were recorded in isolated portal vein. The vascular segments were elongated in 5% increments of the ‘in situ’ length (Lr) up to 1·30Lr. The resting length‐tension curves in male mdxmice were similar to normal mice, while a marked decrease in the slope of the curve was noted in female mdx mice. These findings were not affected by atropine, phentolamine, tetrodotoxin or [Ca2+] in the surrounding media. At Lr, the tension of isolated portal vein was characterized by spontaneous synchronized uniform force waves in normal mouse. In contrast, in mdxmouse portal veins an irregular motor pattern characterized by desynchronized force waves with a decrease of amplitude and an increase in frequency was recorded. Extension of the length of the portal vein segment did not increase the spontaneous phasic activity developed in female mdx mice although this was noted with male mdx mice and normal mice. Experiments with chemical depolarizing agents indicated that spontaneous myogenic excitation activated the great majority of vascular smooth muscle cells in normal mouse portal vein, whereas in mdx mice only a reduced number of these cells were excited suggesting that in the mdx mouse the intercellular electronic coupling is altered. In conclusion this study provides the first description of the mechanical activities of portal vein longitudinal muscle and shows that in mdx mice the motor activity is severely disrupted.