bluuebunny/crossref_metadata_2025 huggingface dataset:
Cinnamate uptake by rat small intestine: transport kinetics and transepithelial transfer
Authors: Ader P , Grenacher B , Langguth P , Scharrer E , Wolffram S
Published: December 2014

Due to their ubiquitous occurrence in the plant kingdom, plant phenolics, including monomeric cinnamic acids, are ingested by man and animals in variable amounts with their natural diets. Recently, Na(+)‐dependent saturable transport of cinnamic acid across the brush‐border membrane of rat jejunum has been described. It was the aim of the present study to characterize this mechanism in more detail. We therefore determined the transport kinetics of mucosal uptake of radioactively labelled cinnamic acid under various conditions using a short‐term mucosal uptake technique. In addition, the transfer of cinnamic acid across the jejunal wall was investigated using everted intestinal sacs. Investigations of the kinetics of cinnamic acid uptake by the mid‐jejunal mucosa revealed the involvement of two transport components, a diffusive Na(+)‐independent mechanism and a saturable Na(+)‐dependent mechanism. The results obtained with everted sacs provided further evidence of the existence of an active Na+ gradient‐driven transport of cinnamic acid across the intestinal epithelium. In the presence of Na+, a significant accumulation of cinnamate occurred inside the serosal compartment and this was strongly inhibited by serosal ouabain. A decrease in the extracellular pH stimulated mucosal cinnamate uptake by increasing the apparent affinity (1/km). This may be attributable to the involvement of a transmembrane H+ gradient in Na(+)‐dependent cinnamate transport because the protonophore FCCP caused a significant reduction of cinnamate uptake only in the presence of Na+. The kinetics of cinnamate transport in the absence or presence of a surplus of either unlabelled cinnamate or unlabelled butyrate indicates a reduction in the apparent affinity of the Na(+)‐dependent mechanism involved in cinnamate uptake. These results may be explained by a modification of the mechanism by the intracellular pH. Additionally, competitive inhibition of cinnamate uptake by substances structurally related to cinnamic acid may also be involved.
Vascular responses to stimulation of carotid, aortic and coronary artery baroreceptors with pulsatile and non‐pulsatile pressures in anaesthetized dogs
Authors: McMahon NC , Drinkhill MJ , Hainsworth R
Published: December 2014

This research was designed to compare coronary, carotid and aortic arch baroreceptors in terms of the ranges of pressures required to elicit reflex vascular responses and the possible differences between the responses to pulsatile and non‐pulsatile stimuli. Dogs were anaesthetized with alpha‐chloralose, artificially ventilated and the chests opened wide. A perfusion circuit allowed independent control of pressures distending the three baroreceptor regions. A cardiopulmonary bypass and ventricular fibrillation prevented cardiac pulsations from influencing coronary baroreceptor pressure. The caudal region of the animal was perfused at constant flow and vascular resistance responses were assessed from changes in perfusion pressure. Only tests in which the overall response exceeded 3 kPa (22.5 mmHg) were analyzed. Reflex responses were obtained to significantly lower coronary pressures than were required to induce responses from other regions. The inflexion points of the stimulus‐response curves for pulsatile coronary, carotid and aortic pressures were 10.5 +/− 0.6, 15.5 +/− 1.8 and 16.4 +/− 1.7 kPa (79 +/− 5, 116 +/− 14 and 123 +/− 13 mmHg, respectively; values are means +/− S.E.M.). When the responses to pulsatile stimuli were compared with those to non‐pulsatile stimuli, it was noted that for the carotid receptors, lower pressures were required to induce responses (inflexion pressure less) and the slope of the stimulus‐response curve was less. Pulsatile aortic pressures induced a parallel (downward) displacement of the curve but no change in inflexion point or slope. The coronary baroreceptor stimulus‐response relationship was unaffected by pulsatility. These results show differences between the characteristics of the three baroreceptors with coronary receptors being unaffected by pressure pulsatility but likely to be of importance in hypotensive situations.
Quantification of efflux into the blood and brain of intraventricularly perfused [3H]thymidine in the anaesthetized rabbit
Authors: Thomas SA , Davson H , Segal MB
Published: December 2014

Studies using choroid plexuses incubated in vitro have led to the conclusion that pyrimidine deoxyribonucleosides, such as thymidine, enter the brain predominantly through the blood‐cerebrospinal fluid (CSF) barrier across the choroid plexuses. In order to examine this hypothesis, ventriculocisternal perfusions were carried out to determine the magnitude of the passage of [3H]thymidine from the CSF into the brain and blood. These experiments demonstrated that approximately 50% of the [3H]thymidine was eliminated from the CSF perfusate, some 41.6 +/− 5.6% passing into the blood and only 7.6 +/− 0.6% to the brain. Efflux into both the blood and brain was saturable, with a Km of 17.8 microM and a Vmax of 0.46 nM min‐1, and partially nitrobenzylthioinosine (NBMPR) sensitive. However, a non‐saturable component did exist (Kd, 13.8 microliters min‐1). Overall, the rapid removal of [3H]thymidine from the CSF and its low uptake from the CSF into the brain suggests that the choroid plexuses would be an inefficient pathway for the entry of this pyrimidine deoxyribonucleoside into the brain.
The validity of the recollection technique in micropuncture experiments on the rat kidney
Authors: Romano G , Favret G , Federico E , Bartoli E
Published: December 2014

We tested the accuracy of the micropuncture technique by performing total collections of tubular fluid followed by immediate recollections from the same site. We studied thirty‐one Wistar rats under different conditions of hydration and during maintenance infusions. To assure constancy of body fluid volumes the experiments were performed during continuous reinfusion of urine. Overall we performed 190 paired collections and immediate recollections from 147 proximal and 43 distal tubules. The mean values measured during the first collection were not different from the paired means obtained by recollection. Mean values (+/‐ S.E.M.) for first collection and recollection were: single nephron glomerular filtration rate (SNGFR), 34.7 +/− 1.3 vs. 34.2 +/− 1.3 nl min‐1, P > 0.42; percentage reabsorption, 74 +/− 1 vs. 73 +/− 1, P > 0.53; absolute reabsorption, 26.4 +/− 1.2 vs. 25.9 +/− 1.2 nl min‐1, P > 0.47; collection rate, 8.4 +/− 0.6 vs. 8.3 +/− 0.4 nl min‐1, P > 0.92. When subdivided according to different physiological conditions and sampling sites, the results for the paired collection‐recollection means were still not significantly different. The regression between collected and recollected SNGFRs had a slope of 0.96, r = 0.85, P < 0.0001. In order to exclude the possibility that urine reinfusion per se could obscure putative differences in collection‐recollection pairs, the effect of urine reinfusion was separately evaluated. We measured the differences obtained in collection‐recollection pairs before and during urine reinfusion in twenty‐eight tubules from eleven rats, a sample size that allows the detection of 10% difference as significant. While SNGFR did not change, percentage reabsorption fell significantly from 76 +/− 3% before infusion to 60 +/− 3% during reinfusion, P < 0.003. We conclude that the recollection technique yields a reproducible estimate of SNGFR and tubular reabsorption, independent of the sampling site and of the technique used for fluid maintenance. Thus, it can be used to study the effect of different manoeuvres on the rate of proximal tubular transport. Urine infusion per se depresses proximal transport compared with that measured during maintenance with equivalent amounts of isotonic saline.
Glucose, lactate and oxygen metabolism in the fetal pig during late gestation
Authors: Fowden AL , Forhead AJ , Silver M , MacDonald AA
Published: December 2014

Using [U‐14C]glucose tracer, rates of umbilical uptake, utilization and production of glucose, and of CO2 production from glucose carbon, were measured in seven chronically catheterized fetal pigs, when the sow was in the fed state, between 100 and 113 days of gestation (term, 114 +/− 2 days). At the same time, rates of umbilical O2 and lactate uptake were determined in all seven fetuses by the Fick principle. The mean fetal rates of umbilical glucose uptake, glucose utilization and CO2 production from glucose carbon were 38.4 +/‐ 4.2, 41.3 +/− 5.2 and 126.9 +/− 12.6 mumol min‐1 (kg fetal body weight)‐1, respectively (n = 7), No glucose production was therefore detected in the fetuses. Production of CO2 from glucose carbon accounted for 37.3 +/− 3.4% (n = 7) of the umbilical O2 uptake, which averaged 340 +/− 13 mumol min‐1 kg‐1 (n = 7). There was also significant umbilical lactate uptake in the fetal piglets when the sow was in the fed state (32.6 +/− 10.4 mumol min‐1 kg‐1, n = 7, P < 0.05). No significant changes in fetal glucose, O2 or lactate metabolism were observed with increasing age towards term. The fetal rates of glucose metabolism and of umbilical uptake of O2 and lactate were not correlated with fetal blood glucose level. Hence, glucose is used for both oxidative and non‐oxidative metabolism in utero and is an important, although not the sole, source of carbon for metabolic processes in the fetal pig during late gestation.
Differential responses of glycogen synthase to ischaemia and ischaemic contraction in human skeletal muscle
Authors: Katz A
Published: December 2014

The importance of metabolic changes associated with contraction in the activation of glycogen synthase (GS) during recovery from exercise in human skeletal muscle has been investigated. Subjects underwent two experimental treatments: 15 s of ischaemic isometric contraction at 66% of maximal force, and 40 min circulatory occlusion. Biopsies were taken from the quadriceps femoris muscle at rest, at the end of each treatment, and 5 min post‐treatment. The decreases in phosphocreatine (approximately 50%), and increases in glucose 6‐phosphate (approximately 3‐fold) and lactate (approximately 8‐fold) were similar during contraction and occlusion, indicating similar degrees of anaerobic ATP turnover and glycogen breakdown. Glycogen breakdown during each treatment was estimated to correspond to < 5% of the basal muscle glycogen content. GS fractional activity decreased approximately 10% after contraction and approximately 30% after occlusion (P < 0.05 vs. contraction). During recovery from contraction, GS fractional activity increased to 20% above the rest value, whereas no further change occurred during recovery from occlusion (P < 0.001 vs. recovery from contraction). These data demonstrate that the increase in GS fractional activity during recovery from isometric contraction does not require significant glycogen breakdown during the contraction, and is not a consequence of the measured metabolic changes associated with the contraction.
Effect of the potassium channel opener ZM260384 on skeletal muscle function during restricted blood flow in the anaesthetized cat
Authors: Wickenden A , Brooks R , Kelly E , Russell K , Kumar P , Poucher SM
Published: December 2014

The aim of the present experiment was to determine whether the potassium channel opener 2‐(2,2‐bis(difluoromethyl)‐6‐nitro‐3,4‐dihydro‐2H‐1, 4‐benzoxazine‐4‐yl)pyridine‐N‐oxide (ZM260384) was capable of accelerating the decline in skeletal muscle function during restricted blood flow in vivo. Cats (3.0‐4.5 kg body weight) were anaesthetized with alphaxalone‐alphadalone and breathed spontaneously following tracheotomy. Isometric tension was measured in the extensor digitorum longus‐anterior tibialis (EDL‐TA) muscle group. Ischaemia was induced by perfusing the hindlimb with the animal's own blood at a rate of 12.5 ml min‐1 using a roller pump and stimulating the common peroneal nerve to induce repetitive submaximal tetanic contractions in the EDL‐TA. The number of stimulation voltage increments required each minute to maintain a constant level of submaximal mechanical output and the time to exhaustion were used as indices of the rate of tension decline. The rate of tension decline in the ischaemic EDL‐TA in the presence of ZM260384 at 3 mg kg‐1, a maximally hypotensive dose predicted to be within the dose range required to exert direct effects on skeletal muscle, was measured and compared with the rate of tension decline in the presence of ZM260384 at 0.03 mg kg‐1, also maximally hypotensive dose but below the predicted dose range for skeletal muscle effects. The number of voltage increments per minute was 1.93 +/− 0.07 and 1.48 +/− 0.14 (P < 0.05) in the presence of 3 and 0.03 mg kg‐1 ZM260384, respectively. Time to exhaustion was 17.5 +/− 4.2 and 7.2 +/− 0.8 min (P < 0.05) in the presence of 3 and 0.03 mg kg‐1 ZM260384, respectively. Given that there was no difference between these two groups in any haemodynamic variable measured, the results of the present study suggest that ZM260384 (3 mg kg‐1) increases the rate of isometric force loss in ischemic skeletal muscle in vivo.
Oxidative stress: oxidants and antioxidants
Authors: Sies H
Published: December 2014

An imbalance between oxidants and antioxidants in favour of the oxidants, potentially leading to damage, is termed ‘oxidative stress’. Oxidants are formed as a normal product of aerobic metabolism but can be produced at elevated rates under pathophysiological conditions. Antioxidant defense involves several strategies, both enzymatic and non‐enzymatic. In the lipid phase, tocopherols and carotenes as well as oxy‐carotenoids are of interest, as are vitamin A and ubiquinols. In the aqueous phase, there are ascorbate, glutathione and other compounds. In addition to the cytosol, the nuclear and mitochondrial matrices and extracellular fluids are protected. Overall, these low molecular mass antioxidant molecules add significantly to the defense provided by the enzymes superoxide dismutase, catalase and glutathione peroxidases.
Endothelial barrier dysfunction and oxidative stress: roles for nitric oxide?
Authors: McQuaid KE , Keenan AK
Published: December 2014

Endothelial dysfunction has an important role to play in the pathophysiology of human vascular disease. The maintenance of barrier function is critical to the role of vascular endothelium in cardiovascular haemostasis and this function can be compromised by inflammatory mediators, cytokines or oxidants. Under conditions of oxidative stress a variety of reactive oxygen species (ROS) may be generated, which increase the permeability of the endothelial monolayer to fluid, macromolecules and inflammatory cells. The endothelium‐derived nitric oxide radical (NO), whose physiological actions include effects on vascular smooth muscle, is normally inactivated by the superoxide radical anion. While large amounts of NO have cytotoxic potential, it is now becoming clear that combinations of NO with ROS can produce either cytotoxic or cytoprotective effects, depending on the relative amounts of each which are present in the target cell or its environment at a particular time. The contribution of NO to oxidant‐mediated endothelial barrier dysfunction can be assessed in vitro in endothelial monolayers grown on porous membrane supports. In this model, using hydrogen peroxide (H2O2) as the oxidant, H2O2‐induced losses of barrier function can be enhanced or partially offset by NO donor drugs, depending on the concentration of NO donor used. Furthermore, the injurious or cytoprotective effects of these agents appear to be determined by the quantity of NO generated. Since NO is administered clinically by inhalation in conditions such as pulmonary hypertension or the adult respiratory distress syndrome, which are themselves associated with generation of ROS, it is likely that low concentrations of NO may protect the pulmonary vascular endothelium while high concentrations might be expected to combine with ROS to yield intermediates capable of causing further endothelial injury or loss of barrier function.
Growth hormone does not affect non‐insulin‐mediated glucose uptake in sheep
Authors: Rose MT , Obara Y , Itoh F , Hashimoto H , Takahashi Y
Published: December 2014

Four adult Merino sheep were used in the experiment, which was divided into four parts. For the 5 days before parts 1 and 3 saline was injected and for the 5 days before parts 2 and 4 growth hormone (GH; 4 mg day‐1 subcutaneously) was injected. In parts 1 and 2 a primed continuous infusion of [6,6‐2H2]glucose and either saline or GH, respectively, were infused for 5 h. The first 3 h was the control period. From 3 to 5 h insulin (0.5 mU kg‐1 min‐1) was infused. Coincident with the insulin infusion, normal glucose was also infused at a variable rate, dependent on the rapidly determined plasma glucose concentration, in order to keep the plasma glucose concentration constant. Parts 3 and 4 of the experiment were the same as parts 1 and 2, respectively, except for the following: the glucose isotope and saline or GH were infused for 7 h, from 3 to 7 h somatostatin (SRIF; 0.417 microgram kg‐1 min‐1) was infused, and from 5 to 7 h insulin was infused. Measurements of glucose turnover were made in the last 40 min of the control, insulin‐only, SRIF‐only and insulin‐plus‐SRIF infusion periods. Plasma insulin levels were reduced to below the level of detection by the SRIF infusion; under such conditions whole body glucose uptake should be entirely non‐insulin mediated (NIMGU). Expressing glucose uptake as glucose metabolic clearance rate revealed that GH had no effect on NIMGU but significantly reduced the level of insulin‐mediated glucose uptake (IMGU). Thus a reduction in the rate of NIMGU is probably not part of the mechanism by which GH repartitions glucose to sites of growth and milk production, whilst the present study confirms the antagonistic effect of GH on IMGU.
Fetal and maternal fluid balance in sheep during hyperthermia with and without water deprivation
Authors: Dickson KA , Harding R
Published: December 2014

Our aim was to determine the effect of maternal hyperthermia, both with and without maternal water deprivation, on fetal fluid balance. Seven pregnant ewes (131.8 +/ࢤ 1.0 days gestation) were studied during a control period and periods of maternal heating (MH, 42‐44 degrees C for 8 h, water freely available), maternal water deprivation (MWD, 30 h) and maternal heating combined with water deprivation (MH + MWD, 30 h deprivation with heating during last 8 h). Relative to control values, MH increased maternal water intake and urine output, and [K+] in fetal plasma and fetal urine. Relative to control values, MH decreased maternal plasma osmolality, [Na+] and [K+]; fetal plasma osmolality and [Na+]; fetal lung liquid [Na+] and [Cl‐]; and fetal production rates of lung liquid and urine. In response to MH + MWD, the osmolality, [Na+] and [Cl‐] of maternal and fetal plasma, fetal lung liquid and fetal urine (excluding urinary [Cl‐]) increased compared with control values. In the fetus, MH + MWD increased plasma and urinary [K+], and decreased production rates of lung liquid and urine compared with control values. During MH + MWD, compared with MH alone, greater alterations were seen in maternal rectal temperature, water input and urine output; osmolality, [Na+] and [Cl‐] of maternal and fetal plasma, fetal lung liquid and fetal urine (excluding urinary [Cl‐]); and fetal urinary [K+]. During MH + MWD, compared with MWD alone, greater alterations were seen in maternal plasma [Cl‐] and [K+]; fetal urinary osmolality and [K+]; and fetal plasma [K+]. Our results show that, when water is available, maternal hyperthermia stimulates ewes to drink substantially more than under normal conditions, thereby decreasing their plasma osmolality; water transfer to the fetus may increase, thereby decreasing fetal plasma osmolality. When drinking water is unavailable, maternal hyperthermia and associated dehydration may decrease water transfer to the fetus. Thus, the fetus becomes not only hyperthermic, but also hyperosmotic and possibly hypovolaemic. Maternal hyperthermia, irrespective of the availability of drinking water, decreases production rates of lung liquid and urine in the fetus.
Parotid secretion daily patterns and measurement with ultrasonic flow probes in conscious sheep
Authors: Meot F , Cirio A , Boivin R
Published: December 2014

Five sheep under halothane anesthesia were prepared with bilateral transit time ultrasonic flow probes around the parotid ducts. The ducts were fitted with non‐obstructive sampling catheters through their oral ends. After probe encapsulation (8 days), salivary flows were continuously recorded (4‐5 days, dual‐channel ultrasonic flowmeter). For rumination, eating, resting and drinking periods, respectively, the parotid daily outputs recorded were 1.96 +/ࢤ 0.57, 0.97 +/ࢤ 0.34, 2.84 +/ࢤ 0.41 and < 0.041 and bilateral flow rates were 6.76 +/ࢤ 0.70, 5.63 +/ࢤ 1.42, 2.50 +/ࢤ 0.58 and 1.69 +/ࢤ 0.88 ml min‐1. An ipsilateral secretory reflex was evident when the sheep changed chewing side during rumination (4.44 +/ࢤ 0.96 ml min‐1 ipsilateral vs 2.63 +/ࢤ 0.90 ml min‐1 contralateral flow, P < 0.01). Secretory patterns are described in detail during rest, eating, drinking and rumination periods. The pH of parotid saliva (8.36 +/ࢤ 0.14) and the osmolality (273.8 +/ࢤ 9.9 mosmol kg‐1) were independent of secretory rates. In situ probe calibration showed high accuracy (0‐9%). The main advantages of the technique are its accuracy and good tolerance, duct integrity and maintenance of nervous supply, minimal surgery, uninterrupted salivary flow, simultaneous bilateral measurements and precise flow monitoring, permitting detailed observations.
The renal response of sheep to intraportal infusion of glucagon
Authors: Faix S , Leng L
Published: December 2014

The effects on renal functions of infusing glucagon (100 ng kg‐1 min‐1) into the portal vein system were studied in young anaesthetized sheep kept on a diet with normal protein and digestible energy contents. The clearance measurements of the left kidney functions showed a decreased urine flow rate (from 0.36 +/ࢤ 0.04 to 0.18 +/ࢤ 0.03 ml min‐1; P < 0.01) within the first 10 min of glucagon infusion, falling to 0.07 +/ࢤ 0.02 ml min‐1 (P < 0.01) during the next 10 min. The glomerular filtration rate also decreased from 17.56 +/ࢤ 2.92 ml min‐1 to its lowest value, 3.34 +/ࢤ 1.02 ml min‐1, (P < 0.01) after 20 min of glucagon infusion. Decreases in urea excretion (from 53.1 +/ࢤ 6.46 to 3.82 +/ࢤ 1.27 mumol min‐1; P < 0.01) and osmotic clearance (from 0.67 +/ࢤ 0.13 to 0.09 +/ࢤ 0.02 ml min‐1; P < 0.01) occurred during the first 20 min. The plasma level of glucose increased from 4.01 +/ࢤ 0.53 to 8.33 +/ࢤ 1.12 mmol l‐1 (P < 0.05) 20 min after the start of glucagon infusion. Twenty minutes after the start of glucagon infusion, the values of all the parameters measured began to recover, although they did not reach the control level, even after 1 h. Blood pressure was stable during the whole experiment. The results show that the effects of intraportally infused glucagon on kidney functions in sheep are the opposite of those obtained from similar experiments in laboratory animals with simple stomachs or in humans.
Reflex vascular responses to alterations in abdominal arterial pressure and flow in anaesthetized dogs
Authors: Drinkhill MJ , Doe CP , Myers DS , Self DA , Hainsworth R
Published: December 2014

The existence of abdominal arterial baroreceptors has long been controversial. Previously difficulties have been encountered in localizing a stimulus to abdominal arteries without affecting reflexogenic areas elsewhere. In these experiments, using anaesthetized dogs, the abdomen was vascularly isolated at the level of the diaphragm, perfused through the aorta, and drained from the inferior vena cava to a reservoir. Changes in abdominal arterial pressure were effected by changing the perfusion pump speed. During this procedure the flow back to the animal from the venous outflow reservoir was held constant. Increases and decreases in abdominal arterial pressure resulted, respectively, in decreases and increases in perfusion pressure to a vascularly isolated hind‐limb and in some dogs also a forelimb. Responses were significantly larger when carotid sinus pressure was high (120‐180 mmHg) than when it was low (60 mmHg). Responses were still obtained after cutting vagus, phrenic and splanchnic nerves, but were abolished by spinal cord lesion at T12. These experiments provide evidence for the existence of abdominal arterial baroreceptors. The afferent pathway for the reflex vasodilatation appears to run in the spinal cord.
The effects of age on kinetics of oxygen uptake and phosphocreatine in humans during exercise
Authors: Chilibeck PD , Paterson DH , McCreary CR , Marsh GD , Cunningham DA , Thompson RT
Published: December 2014

We compared the kinetics of oxygen uptake (VO2) and phosphocreatine (PCr) during the adjustment to and recovery from plantar flexion exercise in moderately active older (n = 10, 66.9 years) and younger (n = 10, 27.5 years) individuals. VO2 kinetics were similar in the two groups, with time constants (tau) averaging 46.3 +/− 10.2 s (younger, on‐transient), 38.1 +/− 14.4 s (younger, off‐transient), 46.3 +/− 17.8 (older, on‐transient) and 40.7 +/− 19.2 s (older, off‐transient). These were similar to corresponding PCr kinetics, measured by 31P nuclear magnetic resonance spectroscopy, which averaged 50.6 +/− 24.0 s (younger, on‐transient), 42.0 +/− 16.1 s (younger, off‐transient), 39.8 +/− 22.0 s (older, on‐transient) and 37.6 +/− 21.6 s (older, off‐transient). On‐transient tau values for VO2 and PCr were correlated, for combined groups (r = 0.53; P = 0.015). We conclude that: (1) VO2 and PCr kinetics during exercise of a muscle group accustomed to daily activity are not compromised in physically active older humans, and (2) PCr kinetics reflect the kinetics of muscle O2 consumption, and are expressed at the lung (VO2 kinetics) after a transit delay.
Proximal reabsorption with changing tubular fluid inflow in rat nephrons
Authors: Romano G , Favret G , Damato R , Bartoli E
Published: December 2014

The relative contribution of intraluminal versus peritubular factors in mediating glomerulo‐tubular balance (GTB) is still controversial. We modulated the load of tubular fluid to the proximal tubule of single nephrons of rats by injecting oil into the efferent arteries (EAO). In fifty nephrons the changes in reabsorption induced by obstruction occurred in the same direction as, and were significantly correlated with, the simultaneous changes in single nephron glomerular filtration rate (SNGFR) (y = ‐0.54 + 0.92x, R = 0.91, P < 0.0001). In an additional set of thirty‐nine nephrons the load of tubular fluid was changed, during EAO, by partial collection from Bowman's space or from the early proximal convolution. Thus, the rate of tubular fluid delivery along the proximal tubule was changed in an experimental situation that prevented any modification in the oncotic pressure of peritubular capillaries. The changes in proximal deliveries during this experimental condition were significantly correlated with those during reabsorption (y = ‐2.87 + 0.71x, R = 0.82, P < 0.0001). These data demonstrate that GTB is fully expressed even when the native peritubular environment is kept constant while the rate of perfusion of proximal tubular segments with native tubular fluid is changed.
Altered [3H]ouabain binding to cardiac muscle in insulin‐dependent and non‐insulin‐dependent diabetic rats
Authors: Banyasz T , Kovacs T
Published: December 2014

The aim of this study was to determine the ouabain receptor density, Na+,K(+)‐ATPase function and contractile properties of cardiac muscle in insulin‐dependent and non‐insulin‐dependent rat diabetes mellitus (IDDM and NIDDM, respectively) and the reversibility of the diabetes‐induced changes by insulin or thyroxin substitution. IDDM and NIDDM were induced in Wistar rats by streptozotocin injection. Contractile parameters were measured in isolated left ventricular trabeculae. [3H]Ouabain binding to myocardium was measured in right and left ventricular strips obtained from diabetic animals and their age‐matched controls. Both the maximum [3H]ouabain binding capacity (Bmax) and the Kd for [3H]ouabain binding, as well as maximum 86Rb+ uptake and rate of contraction, were decreased in IDDM myocardium compared with controls. Insulin or thyroxin substitution reversed the reduction in Bmax and contraction rate, but not the decrease in Kd. In young, but not old, control animals, both Bmax and maximum 86Rb+ uptake were higher in the right ventricular myocardium than in the left one. In contrast to changes observed in IDDM, both Bmax and Kd for [3H]oubain binding were increased in the left but not in the right ventricle of NIDDM animals. NIDDM caused no alterations in contractile properties. Prominent differences were observed in [3H]ouabain binding characteristics and myocardial contractility between young and old control animals. Bmax of [3H]ouabain binding and rate of contraction were inversely proportional in all preparations studied. It is concluded that IDDM and NIDDM induce different alterations in myocardial Na+,K(+)‐ATPase, and these changes may influence the contractile properties of cardiac muscle.
Membrane‐bound glyceraldehyde‐3‐phosphate dehydrogenase and multiphasic erythrocyte sugar transport
Authors: Heard KS , Diguette M , Heard AC , Carruthers A
Published: December 2014

Net sugar import by human erythrocytes consists of ATP‐modulated rapid and slow phases while sugar export consists of a single slow phase. We have proposed that this behaviour results from obligate substrate tunnelling from transporter to bulk cytosol through a complex containing high‐affinity, low‐capacity sugar binding sites (Cloherty, Sultzman, Zottola & Carruthers, 1995). Glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) is known to compartmentalize ATP delivery to erythrocyte membrane ATPases and interact directly with the erythrocyte glucose transporter in vitro. The present study examines the possibility that GAPDH is an obligate component of the hypothesized sugar‐binding complex. GAPDH remains associated with the erythrocyte membrane following cell lysis and remains associated with the cytoskeleton under conditions where more than 99% of the membrane glucose transport protein (GLUT1) is released by detergent (Triton X‐100). GAPDH is released from erythrocyte membranes upon exposure to Mg.ATP or to NADH. ATP displacement of membrane‐bound GAPDH is half‐maximal at 200 microM ATP and appears to involve ATP interaction with multiple, co‐operative sites. GAPDH interaction with purified tetrameric GLUT1 is saturable, co‐operative and also inhibited by ATP. ATP inhibition of GAPDH binding to purified tetrameric GLUT1 is less effective than ATP inhibition of GAPDH binding to intact erythrocyte membranes. Removal of cellular GAPDH by exposing erythrocyte membranes to NADH prior to membrane resealing neither affects ATP modulation of sugar transport nor reduces biphasic net sugar uptake to a single phase. We conclude that ATP‐sensitive GAPDH interaction with the cytoplasmic surface of erythrocyte membranes and GLUT1 is responsible neither for ATP modulation of sugar transport nor for multiphasic net sugar import by human red cells.
Evidence from temperature studies that the human erythrocyte hexose transporter has a transient memory of its dissociated ligands
Authors: Naftalin RJ
Published: December 2014

The inhibition constant of L‐sorbose efflux (Ki(sorbose)) from human erythrocytes for inhibition by D‐glucose increases from 5.15 +/− 0.89 to 12.24 +/− 1.9 mM on cooling from 50 degrees C to 30 degrees C; the Ki(sorbose) of D‐mannose increases similarly on cooling. The activation energy Ea(sorbose) of net L‐sorbose exit from human erythrocytes is 62.9 +/− 3.1 kJ mol‐1; but in the co‐presence of 5 mM D−glucose Ea(sorbose) is reduced to 41.7 +/− 1.6 kJ mol‐1 (P < 0.005). These data are consistent with the view that when D‐glucose binds to the hexose transporter it leads to an activated transporter state which remains transiently activated after glucose dissociates; if L‐sorbose binds to the excited state it is more mobile than otherwise and consequently the apparent Ki(sorbose) of D‐glucose is raised. Cooling prolongs the decay time of the activated state; hence the Ki(sorbose) of D‐glucose rises as temperature is reduced.
Comparison of extrinsic and intrinsic neuromodulation in two central pattern generator circuits in invertebrates
Authors: Katz PS
Published: December 2014

There are many sources of modulatory input to CPGs and other types of neuronal circuits. These inputs can change the properties of cells and synapses and dramatically alter the production of motor patterns. Sometimes this enables the production of motor patterns by the circuit. At other times, the modulation allows alternate motor patterns to be produced by a single circuit. Modulatory neurones have fast as well as slow actions. In some cases, such as with GPR, the two types of effects are due to the release of co‐transmitters. In other cases, such as with the DSIs, a single substance can act at different receptors to cause fast and slow postsynaptic actions. The effect of a neuromodulatory neurone is determined by the type of receptor on the target neurone. Thus a single modulatory neurone evokes a suite of actions in a circuit and thereby produces a co‐ordinated output. Extrinsic and intrinsic sources of neuromodulation have different sets of constraints acting upon them. For example, extrinsic neuromodulation can easily be used for motor pattern selection; a different pattern is produced depending upon which modulatory inputs are active. However, intrinsic neuromodulation is not well suited to that task. Instead, it is useful for self‐organizing properties and experience‐dependent effects. One clear conclusion from this work and other work in the field is that neuromodulation by neurones intrinsic and extrinsic to CPGs is not uncommon (Katz, 1995; Katz & Frost, 1996). It is part of the normal process of motor pattern generation. As such, it needs to be considered when discussing mechanisms for neuronal circuit actions.
Calcium‐inhibitable current in cultured embryonic chick cardiac myocytes: possibly via a novel chloride channel
Authors: Liu SJ , Stimers
Published: December 2014

The role of extracellular Ca2+ (Ca(2+)o) in the modulation of cardiac Cl‐ currents (I(Cl)) such as those activated by cAMP or swelling is uncertain. The effects of Ca(2+)o and extracellular cadmium (Cd(2+)o) on Cl‐ currents in cultured chick cardiac myocytes were investigated in Na+− and K+−free internal and external solutions using the whole‐cell patch‐clamp technique. In the absence of Na+ and K+ internally and externally, the whole‐cell current was predominantly I(Cl). In the absence of cAMP, removal of Ca(2+)o (+ 1 mM EGTA) resulted in an increase in the current that was suppressed by reduction of Cl(o)‐ with a rightward shift of the zero‐current potential towards the CI‐ reversal potential. We designated this current as a Ca2+−inhibitable I(Cl). Addition of 0.5 mM Cd(2+)o with or without removal of Ca(2+)o also resulted in a 1.5− to 2.0‐fold increase in I(Cl) that was attenuated by 1 mM DIDS (4,4'−diisothiocyanatostilbene−2,2'−disulphonic acid). Under similar conditions, I(Cl) activated by Cd(2+)o (in 1 mM Ca(2+)o solution) was not further increased by subsequent removal of Ca(2+)o, suggesting that addition of Cd(2+)o and removal of Ca(2+)o activated the same I(Cl). In contrast, exposure to 1 microM forskolin further enhanced I(Cl) in the presence of Cd(2+)o. With 10 microM cAMP in the pipette solution, Ca2+−inhibitable I(Cl) could be activated in myocytes that do not possess cAMP‐activated Cl‐ channels, indicating that activation of Ca2+−inhibitable I(Cl) does not require cAMP. In the presence of cAMP, in cells that display the cAMP‐activated I(Cl), removal of Ca(2+)o resulted in a further increase in I(Cl) comparable to the Ca2+−inhibitable I(Cl). The Ca2+−inhibitable I(Cl) was minimized when pipette solutions contained 1.5 microM Ca2+. These results suggest that removal of Ca(2+)o or application of Cd(2+)o activates a Ca2+−inhibitable I(Cl) that is distinct from the cAMP‐activated I(Cl).
Differential effects of hypoxia on the intracellular Ca2+ concentration of myocytes isolated from different regions of the rat pulmonary arterial tree
Authors: Bakhramov A , Evans AM , Kozlowski RZ
Published: December 2014

Hypoxic pulmonary vasoconstriction (HPV) may be mediated, in part, by an oxygen‐sensing mechanism intrinsic to pulmonary arterial smooth muscle. It has been proposed that hypoxia inhibits a K+ conductance, which promotes membrane depolarization, subsequent activation of L‐type Ca2+ channels and ultimately constriction. We have monitored hypoxia‐induced changes in the intracellular Ca2+ concentration ([Ca2+]i) of single myocytes isolated from the rat pulmonary arterial tree using microspectrofluorimetry and ratiometric measurement of indo‐1 fluorescence. The basal level of [Ca2+]i was in the range 35–80 nM and cells were quiescent at rest exhibiting no spontaneous oscillations in [Ca2+]i. When the extracellular K+ concentration ([K+]o) was raised to 20 mM, the [Ca2+]i increased from approximately 60 to approximately 100 nM. This increase was abolished by nifedipine, demonstrating the presence, and need for activation, of functional voltage‐gated L‐type Ca2+ channels. Hypoxia (PO2 < or = 30 mmHg; throughout) had little effect on the resting [Ca2+]i in myocytes isolated from either the main intrapulmonary artery, or its primary, secondary or tertiary branches. However, upon raising the [Ca2+]i by increasing [K+]o to 20 mM, hypoxia was found to lower [Ca2+]i from approximately 110 to approximately 70 nM, in cells isolated from the main conduit and primary branches of the intrapulmonary artery. In marked contrast, when [Ca2+]i was raised, by increasing [K+]o to 20 mM, in myocytes isolated from secondary and tertiary branches of the intrapulmonary artery, hypoxia induced a further reversible increase in the [Ca2+]i from approximately 160 to approximately 240 nM. Neither hypoxia alone nor in combination with 20 mM K(+)o induced any increase in the [Ca2+]i in the presence of nifedipine. We conclude that hypoxia may modulate [Ca2+]i in rat pulmonary artery myocytes only following its elevation by a depolarizing stimulus.
Site of catecholamine modulation of feto‐maternal electric potential difference in the pig
Authors: Ward BS , Glazier JD , Sibley CP , Boyd RD
Published: December 2014

Feto‐maternal vascular (PD(F‐M)) and amniotic maternal (PD(A‐M)) potential differences were measured simultaneously on seven occasions in six conscious pigs of 100–106 days gestation. Resting values of PD(F‐M) and PD(A‐M) were not significantly different although the range was wide. Fetal intravascular injection of 20 microg adrenaline, but not of saline, was associated with a prompt reversible change, of equal magnitude, in both PD(F‐M) and PD(A‐M). In some experiments polarity was reversed. Feto‐amniotic potential difference did not change. There was no change in fetal plasma K+ and Na+ concentrations. Because of the simultaneous and equal alterations in PD(F‐M) and PD(A‐M) following adrenaline and the anatomical configuration of the pig conceptus, we conclude that the catecholamine modifiable component of PD(F‐M) is generated by electrogenesis in the pig placenta, probably by its chorionic (trophoblastic) cell layer.
An improved technique for studying pleural fluid pressure and composition in rabbits
Authors: Del Fabbro M
Published: December 2014

Knowledge of pleural liquid pressure (Pliq) and composition is crucial for studies concerning intrapleural fluid dynamics, and pleural fluid turnover. We measured Pliq at intercostal and costal levels in anaesthetized spontaneously breathing rabbits using a minimally invasive method that assures a long‐lasting hydraulic continuity between the pleural liquid and the recording system. Polyethylene tubes were glued either to the exposed endothoracic fascia or inserted into a rib to provide a scaled connection to the recording system. After inducing a pneumothorax with nitrous oxide (N2O) via an intrapleural cannula, a hole (approximately 0.7 mm2) was pierced in the parietal pleura through the tube lumen. The tubes were then connected to pressure transducers and the whole system was filled with heparinized saline to the level of the parietal pleura; finally the pneumo‐thorax was removed after N2O washout and Pliq recordings were performed. A different kind of tube was used to obtain microsamples of pleural fluid (2.5‐3 microliters) during spontaneous breathing; colloid osmotic pressure of the microsamples (pi liq) was measured with an osmometer, and averaged 9.3 +/− 1.5 cm H2o (n = 70 samples). When pooled and plotted against lung height end‐expiratory intercostal and costal Pliq data scattered along a single regression line with a slope of ‐0.83 and ‐0.90 cm H2O cm(‐1) in supine and prone animals, respectively. End‐inspiratory costal Pliq was significantly more subatmospheric than intercostal in the ventral region of the chest (P < 0.05), and less subatmospheric in the dorsal region, regardless of posture. The techniques presented here could be helpful in gaining a greater insight into the physiology and pathophysiology of the pleural space in terms of pleural fluid dynamics and turnover.
The role of nitric oxide in the control by the vagal nerves of the heart of the ferret
Authors: Conlon K , Collins T , Kidd C
Published: December 2014

This study focuses on the potential role for nitric oxide on the actions of the parasympathetic innervation to the heart. Earlier, we showed that the nitric oxide synthase (NOS) inhibitor N omega‐nitro‐L‐arginine methyl ester (L‐NAME) reduced the bradycardia induced by stimulation of vagal efferent motor fibres and that these effects are reversible through administration of the NOS substrate L‐arginine. In the present study, we show that D‐arginine does not reverse the effects of the inhibitors and confirm that they are reversed by L‐arginine. Another NOS inhibitor, NG‐nitro‐L‐arginine (L‐NOARG), produced similar effects which were not reversed by L‐arginine. In an examination of the effect of increasing NO availability with the NO donor sodium nitroprusside the vagally induced bradycardia was enhanced at all frequencies tested. In a separate series, the effects of NOS inhibitors and NO donors on the dromotropic actions of the vagus were examined. The NOS inhibitor L‐NAME, reduced the increase in atrio‐ventricular conduction delay normally induced by efferent vagal stimulation at all frequencies tested both in the ‘paced’ and ‘unpaced’ heart. Further, sodium nitroprusside enhanced this delay. Overall the study indicates that NO has an important facilitatory role on both the chronotropic and dromotropic actions of the vagus nerve on the heart and that NO may be a rate‐limiting factor in the cardiac responses to vagal stimulation.
Blood mobilization from the liver of the anaesthetized dog
Authors: Noble BJ , Drinkhill MJ , Myers DS , Hainsworth R
Published: December 2014

The abdominal circulation contains a high proportion of the total blood volume and this can change either passively in response to changes in vascular distending pressure or actively (termed a capacitance response) to changes in sympathetic nervous activity. The liver is the largest abdominal organ and this study was designed to evaluate its potential contribution to overall vascular capacitance and compliance. In chloralose anaesthetized dogs, the liver was vascularly isolated, perfused through the portal vein and hepatic artery at either constant pressures or constant flows and drained from the hepatic veins at constant pressure. Changes in vascular resistance were assessed from changes in inflow pressures or flows and hepatic blood volume was determined by differences between net inflow and outflow. During constant flow perfusion the change in hepatic volume (capacitance change) in response to supramaximal stimulation of sympathetic nerves at 16 Hz was (mean +/− S.E.M.) ‐2.40 +/− 0.61 ml (kg body weight)‐1. This response was not significantly different during constant pressure perfusion. The changes in portal venous and hepatic arterial pressures during stimulation at constant flow perfusion were +0.67 +/− 0.13 and +4.92 +/− 0.67 kPa, respectively. The compliance of the liver, assessed as the change in volume to a change in hepatic venous pressure, was +5.44 +/− 0.18 ml kg‐1 kPa‐1. These results indicate that the liver has a major capacitance role, comparable to that of the canine spleen and, in addition, is highly compliant. No evidence was found to suggest that a sphincter on the hepatic outflow exists. Assuming similar responses occur in humans, who do not possess a large contractile spleen, the liver would be the most important controllable blood reservoir in the body.
The role of nitric oxide in the control of protein secretion in the parotid gland of anaesthetized sheep
Authors: Hanna SJ , Edwards AV
Published: December 2014

Parotid secretion has been investigated in anaesthetized lambs in the presence and absence of N omega‐nitro‐L‐arginine methyl ester (L‐NAME) and sodium nitroprusside to block de novo synthesis of nitric oxide (NO). Following administration of L‐NAME the basal rate of flow was unaffected and changes in electrolyte secretion failed to achieve statistical significance but there was a significant fall in the basal rate of protein secretion. The flow of parotid saliva which occurred in response to stimulation of the parasympathetic innervation was reduced by 34% and sodium output was reduced in approximately the same proportion. L‐NAME had no significant effect on these parameters during stimulation of the sympathetic innervation. During combined stimulation of the parasympathetic and sympathetic innervations L‐NAME caused a reduction in parotid salivary flow and sodium output which was roughly the same as that observed during parasympathetic stimulation alone. However, L‐NAME caused a much greater reduction in protein output during each of these experimental protocols: ‐92% during parasympathetic stimulation, =63% during sympathetic stimulation, and ‐60% during combined stimulation. Whereas the absolute amount of protein secreted was reduced after L‐NAME in each instance, the extent of potentiation of protein output recorded during combined stimulation was increased roughly fivefold. It is concluded that the output of protein in response to autonomic stimulation exhibits a greater No dependence than either the flow of saliva or secretion of electrolytes in this gland.