bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on the Mechanism of Action of Lithium Ions
Authors: Giacobini E. , Hovmark S. , Stepita‐Klauco M. 
Published: December 2008

AbstractThe complete replacement of the extracellular Na+ by lithium (Li+) (in 7.8 mM K+ medium) leads to an accumulation of Li+, and a simultaneous decrease in Na+ and K+ in the stretch receptor neuron. Li+ replacement in a medium with a lower K+ concentration (2.4 mM) decreases the quantities of both K+ and Li+. The possibility of a K+ sensitive carrier transporting Li+ into the cell is suggested.
Regional Distribution of Red Cells, Plasma and Blood Volume in the Intestinal Wall of the Cat
Authors: Jodal Mats , Lundgren Ove 
Published: December 2008

AbstractThe distribution of red cells, plasma and blood volume in the wall of the small intestine and in the colon was determined by means of 51Cr‐labelled red cells and 125I‐labelled serum albumin. It was demonstrated that the submucosal tissue layer was the most vascularized. Assuming a total blood content in the intestinal and colonic wall of 5 ml blood/100 g tissue, the regional blood content in the submucosa could be calculated to 10–20 ml/100 g tissue, while the blood content of the mucosa and muscularis amounted to approximately 3 ml/100 g.
Ventilatory Responses to Hypoxia and Hypercapnia with External Airway Resistance
Authors: Barnett Thomas B. , Rasmussen Birger 
Published: December 2008

AbstractThe effects of added external airway resistance upon the steady state ventilatory response to hypoxia and hypercapnia were studied in three normal human subjects. The slope of the stimulus‐response line for CO2 was reduced in all subjects when this resistance was added to the airway. The ventilatory response to eucapnic hypoxia was measured in the same subjects with and without the same added external airway resistance. When end‐tidal carbon dioxide tension was maintained at the normal level by addition of CO2 to the inspired air, the ventilatory response to hypoxia was less in all subjects with added airway resistance than without. For purposes of comparison the level of hypoxia and of hypercapnia that were associated with hyper‐ventilation of 12 1/min were considered to be physiologically equivalent stimuli. At this stimulus level the magnitude of the effect of the same added airway resistance was greater in all subjects during hypercapnia than during hypoxia. These observations suggest that the ventilatory response to hypoxia is less dependent upon the resistive work of breathing than is the response to hypercapnia.
Discharge Patterns in Human Muscle Spindle Afferents during Isometric Voluntary Contractions
Authors: Vallbo Å. B. 
Published: December 2008

AbstractUnitary nerve impulses were recorded from the median nerve of waking human subjects with percutaneously inserted tungsten electrodes. Activities from 63 muscle spindle endings were studied during isometric voluntary contractions. Three main types of response patterns were encountered: a sustained increase of the discharge, a sustained decrease, and a weak discharge consisting of a few impulses. It was concluded that the sustained increase of the discharge was accounted for by an increase of the fusimotor activity, whereas the sustained decrease was accounted for by mechanical unloading. The weak discharge might be accounted for by either mechanical or fusimotor mechanisms. Fusimotor activation concomitant with the skeletomotor activity could be demonstrated for 81% of the spindle afferents. One particular response pattern was not characteristic for certain endings but many units responded with different patterns depending upon the intensity and spatial extent of the contraction. Analyses of the unitary responses to the contraction of different muscle portions indicated that there was a close spatial correspondence in the muscle between the skeletomotor activity and the fusimotor activity.
Metabolic Effects of Prolonged Sympathetic Nerve Stimulation in Canine Subcutaneous Adipose Tissue
Authors: Fredholm Bertil B. , Karlsson Jan 
Published: December 2008

AbstractThe release of glycerol, free fatty acids (FFA), lactate, pyruvate and CO2as well as the uptake of glucose and O2was investigated in canine subcutaneous adipose tissue perfused with blood at a constant rate. Biopsy specimens were analyzed for lactate and glycogen content. Water was found to constitute 17±4 per cent of the wet weight. In unstimulated adipose tissue net glycerol release was 0.25±0.03 and net FFA release 0.12±0.06 μmoles/min/100 g adipose tissue. Both increased during sympathetic nerve stimulation for 50 min. The release of FFA and glycerol was enhanced by inhibition of adrenergic α‐receptors (dihydroergotamine 75–150 μg i.a.) and abolished by blockade of adrenergic β‐receptors (propranolol 400 μg i.a.). Basal glucose uptake averaged 1.4 μmoles/min/100 g tissue and was not significantly affected by nerve stimulation either before or after receptor blockade. The glycogen content, which averaged 3 μmoles glucose/g tissue during basal conditions, decreased by 30 per cent during sympathetic nerve stimulation, provided β‐receptors were not inhibited. During nerve stimulation lactate accumulated in adipose tissue and there was an increased net release of lactate into the blood. These effects were inhibited by either α‐ or β‐receptor blockade. During basal conditions 2.4±0.6 μmoles O2were extracted per min per 100 g tissue. The extraction decreased upon nerve stimulation provided α‐receptors were intact and increased if they were inhibited.The results indicate that stimulation of adrenergic β‐receptors in adipose tissue causes lipolysis and glycogenolysis and that this mobilization when combined with α‐adrenergic vasoconstriction leads to increased production and accumulation of lactate.
Adrenocorticoid regulation of Na+, K+‐ATPase in adult rat kidney: effects on post‐translational processing and mRNA abundance
Authors: CELSI G. , STÅHL J. , WANG Z. ‐M. , NISHI A. 
Published: December 2008

The mechanisms by which adreno‐corticoid hormones regulate Na+, K+‐ATPase in adult kidney were studied in adrenalectomized (Adx) rats. Five days after adrenalectomy, Na+, K+‐ATPase activity was significantly reduced in the renal cortex homogenate (C = 13.0±0.8 vs. Adx = 7.1±0.7 μmol Pi mg‐1 protein h‐1) and in renal microsomes (C = 30.3 ± 1.9 vs Adx = 14.6 ± 1.3 μmol Pi mg‐1 protein h‐1). Glucocorticoid replacement treatment of adrenalectomized rats with betamethasone (20 μg kg‐1 body wt twice daily for 5 days) effectively counteracted the observed reduction in Na+, K+‐ATPase activity. In cortical homogenate the protein level of α1 and β1 subunits measured in immunoblots was not significantly different in Adx and control rats, indicating that 5 days after adrenalectomy the α1 and β1 subunits were present in renal cortical cells to almost normal extent but could not be assembled into a transmembrane functional unit. In support of this conclusion we found that the protein level of both the α1 and β1 subunits was significantly lower (P < 0.001 for both subunits) in microsomes from Adx than in control rats. The mRNA abundance for α1 and β1 subunits were not lower in Adx as compared to control rats 1 and 5 days after surgery. However, if Adx rats were given a single dose of betamethasone (600 μg kg‐1 body wt), a significant 2‐fold increase in both α1 and β1 mRNAs was observed (P < 0.05 for both subunits).These data suggest that glucocorticoids can upregulate the mRNA of both Na+, K+‐ATPase subunits but that the low renal Na+, K+‐ATPase activity in adult Adx rats is mainly due to loss of glucocorticoid regulation of the post‐translational processing of the enzyme.
Postural changes in atrial natriuretic peptide (ANP) and fluid balance in conscious goats
Authors: KOKKONEN U.‐M. 
Published: December 2008

To gain insight into how weak physiological stimuli suffice to release ANP, the effects of 15° head‐up and head‐down tilt, 90 min each in succession, on plasma atrial natriuretic peptide (ANP), plasma cortisol, plasma and urinary Na, K and osmolality, plasma proteins and haematocrit were studied in five conscious goats before and after 2 wk daily training for the tilting procedure.In the trained goats the 15° tilt did not affect the plasma ANP, cortisol or the urine excretion significantly. Total plasma proteins decreased significantly. In the untrained goats, on the other hand, an increasing trend was observed in the plasma ANP and cortisol as well as in the urine Na excretion during the head‐up tilt. During the head‐down tilt, the levels of ANP and Na excretion remained elevated. The plasma ANP was significantly increased after 40 min, by 28% as compared to the pre‐tilting level. The plasma cortisol was first elevated, but then returned to the starting level. The results suggest that in the trained goats the responses to tilting were unmasked. Despite minor effects of the 15° tilt in itself, increased plasma ANP seemed to be associated with increased natriuresis.
Is the mean power frequency shift of the EMG a selective indicator of fatigue of the fast twitch motor units?
Authors: GERDLE B. , FUGL‐MEYER A. R. 
Published: December 2008

During repeated maximum isokinetic contractions parallel decreases in output and the mean power frequency (MPF) of the electromyogram (EMG) occur, followed by stable levels (the endurance level). This study aimed to investigate if hypoxia of the plantar flexors will result in a shift in MPF during the endurance level.Mechanical performance and simultaneous surface EMG activity of three plantar flexors (m. soleus, m. gastrocnemius medialis and m. gastrocnemius lateralis) were recorded during repeated isokinetic plantar flexions at 1.05 rad s‐1 in 10 healthy women. The study consisted of two tests with 14 days in between:(1) a maximum test consisting of 125 maximum plantar flexions. After 100 contractions, using a tourniquet, a relative ischaemia (hypoxia) was induced.(2) a submaximum test performed at the level established between contractions 70–100 of the maximum test, consisting of 125 plantar flexions.During the maximum test mechanical performance output, the signal amplitude (RMS) of the EMG and the MPF decreased in parallel during the initial 50 contractions followed by stable levels during the subsequent 50 contractions. When hypoxia was induced decreases in mechanical performance and RMS appeared without significant decreases in MPF.The present study indicates that the MPF shift is mainly sensitive to biochemical changes in the type 2 fibres. Hypoxia mainly located to the type 1 fibres will not be detected using the MPF variable.
Differential responses in post‐ and pre‐ganglionic adrenal sympathetic nerve activity and renal sympathetic nerve activity after injection of 2‐deoxy‐d‐glucose and insulin in rats
Authors: CARLSSON S. , SKARPHEDINSSON J. O. , DELLE M. , HOFFMAN P. , THORÉN P. 
Published: December 2008

The aim of the study was to compare pre‐ganglionic adrenal nerve activity (pre‐aSNA) to post‐ganglionic adrenal nerve activity (post‐aSNA) in rats after administration of 2‐deoxy‐d‐glucose (2‐DG, 500 mg kg‐1, i.v.), which mimicks a central hypoglycaemia or to the response in pre‐aSNA and post‐aSNA to hypoglycaemia after injection of insulin (5U). Renal postganglionic sympathetic nerve recordings (rSNA) in a separate group was used as a reference.Adrenal or renal multifibre nerve activity was recorded in chloralose‐anaesthetized Wistar‐rats. Trimethaphan, a short‐lasting ganglionic blocker, was administered i.v. (10 mg kg‐1) in order to test for pre‐ or post‐aSNA in the adrenal nerves. The adrenal nerves was considered to contain predominantly post or preganglionic fibres, respectively if the nerve activity in the adrenal nerve decreased (post‐aSNA) or increased (pre‐aSNA). In contrast, all renal nerves showed almost a pure postganglionic activity.Post‐aSNA responded with a tendency to increase after the 2‐DG injection. The highest value (percentage change from control) 5 min after injection was 12 ± 9%. The pre‐aSNA increased with values of 99 ± 52% at 3 min and 86 ± 31% at 5 min (percentage change from control). The activity in the rSNA was only slightly decreased after the injection of 2‐DG when compared to pre‐drug control activity. There was a significant difference between the pre‐aSNA vs. post‐aSNA at 1 min (P < 0.05), 3 min (P < 0.01) and 5 min (P < 0.05).Insulin caused an increase in post‐aSNA with the maximum level of 154 ± 8% reached at 40 min compared to pre‐aSNA, which increased substantially and reached a peak value of 349 ± 43% at 50 min. RSNA was also increased with a maximum level, 160 ± 29% at 50 min (P < 0.01). There was a significant difference in the main effect in pre‐aSNA vs. post‐aSNA.Thus, this study gives further evidence that the adrenal gland is innervated by both post‐ and pre‐ganglionic fibres with different characteristics.
Myocardial force interval relationships: influence of external sodium and calcium, muscle length, muscle diameter and stimulation frequency
Authors: MÖRNER S. E. J. N. , WOHLFART B. 
Published: December 2008

Several inotropic interventions were studied in thin papillary muscles under dynamic conditions. The effects on mechanical restitution and postextrasystolic potentiation were analysed. The decay of postextrasystolic potentiation was taken as a measure of recirculation fraction of activator calcium. The mechanical restitution curve had a plateau phase on its rising phase which was abolished in low extracellular sodium hut pronounced in increased extracellular calcium. The recirculation fraction (RF) in control was 0.35±0.03; lowering the extracellular sodium by 200, increased the RF to 0.46±0.04 (n= 10). A reduction of sodium by 40%, increased the RF to 0.57±0.04, whereas increasing extracellular calcium to 4 mm gave an RF of 0.48±0.05 (n= 10 in all cases). There was no significant effect on RF of changing basic stimulation frequency or muscle preparation length. These findings support RF as a good index of myocardial contractility. Furthermore, at muscle diameters above 0.65 mm the RF was found to he reduced, suggesting this diameter as critical for muscle function. Also, postextrasystolic potentiation in relation to preceding steady state contraction was markedly increased at these diameters.In conclusion, this study shows that RF is independent of stimulation frequency and muscle length, and that it is increased when calcium extrusion by the sodium/calcium exchange is reduced. Furthermore, RF is critically dependent upon the diameter of the preparation and mechanical restitution is changed by altered extracellular sodium concentration.
Pressure/flow relation in the peripheral pulmonary vascular bed in dogs: a preliminary study
Authors: SCHRIJEN F. , SAUNIER C. , HENRIQUEZ A. 
Published: December 2008

In order to test a technique for the determination of the pressure/flow relationship in the peripheral pulmonary vascular bed, the perfusion pressure changes with increasing and then decreasing flow in a small part of the lung (around 1 ml) were studied in anaesthetized supine dogs, after insertion of a specially designed double distal lumen Swan–Ganz catheter. One lumen was used for the pressure measurement, one for infusion of saline by a pump with variable flow, from 0.1 to 1.0 ml s‐1. A conventional thermodilution Swan–Ganz catheter was also advanced in the pulmonary artery, to measure pressures in the pulmonary circulation as well as cardiac output. During infusion in the wedged catheter, right atrial, pulmonary arterial and balloon occlusion wedge pressures did not change. The pressure/flow curve of the occluded vascular bed showed a shape similar to that of collapsible tubes, with a pressure plateau at high flow, but this could also be due to vascular recruitment. The curve exhibited hysteresis, with a lower pressure when flow decreased. The slope of the initial part of the curve increased, on average, from 54±9 during normoxia to 91±27 mmHg s ml‐1during hypoxia (FIO2= 0.10); this difference was not significant, but the perfusion pressure at high flow was significantly higher during hypoxia (P < 0.05).Using blood instead of saline would allow the determination of the peripheral pulmonary vascular resistance under physiological conditions, and further work is needed to estimate the sensitivity and the reproducibility of this technique.
Effects of cromakalim (BRL 34915) on resting and evoked activity in frog semicircular canals
Authors: ZUCCA G. , BOTTA L. , BARBIERI A. , GRANA E. , VALLI P. 
Published: December 2008

The effects of endolymphatic administration of cromakalim and glibenclamide were tested in isolated semicircular canals of the frog. The actions of the drugs were evaluated by recording: (1) the transepithelial potential between the endolymphatic and the perilymphatic sides of the crista ampullaris; (2) the slow nerve potential from the ampullar nerve; (3) the action potential discharge in afferent ampullar nerve fibres; and (4) the perilympathatic potassium concentration in the fluid bathing the outer surface of the crista ampullaris.The above mentioned parameters were recorded both at rest and during mechanical stimulation of the sensory organ.The results demonstrated that the endolymphatic administration of cromakalim (10‐4M) produced an increase in both ampullar receptor resting activity and in perilymphatic K+resting levels. By contrast all the parameters related to the mechanically evoked responses were practically unaffected. Glibenclamide (10‐4M) proved able to cancel or to prevent cromakalim effects. These data suggest that the membrane of the hair cells is endowed with K+channels regulated by internal ATP whose activation is mainly involved in the processes sustaining ampullar receptors' resting firing rate.
Functional and stereologic estimations of myocardial capillary exchange capacity in treated and untreated spontaneously hypertensive rats
Authors: WÅHLANDER H. , NORDBORG C. , NORDLANDER M. , FRIBERG P. 
Published: December 2008

Myocardial capillary exchange capacity was investigated by stereologic and functional techniques in parallel during pressure‐overload cardiac hypertrophy and after long‐term antihypertensive therapy with the vasodilator felodipine. In 26‐week‐old female spontaneously hypertensive rats (SHR) blood pressure increased by 25 % and left ventricular weight (LVW/BW) increased by 18% compared to Wistar‐Kyoto rats (WKY). Myocardial capillary surface and volume densities normalized for organ weight were similar in both ventricles for both strains. Moreover, capillary surface density was higher sub‐epicardially (EPI) than in the subendocardium (ENDO) in the left ventricle of SHR. Thirteen weeks of felodipine‐therapy (SHR‐Felo) normalized blood pressure without affecting LVW/BW although a transition from concentric to eccentric hypertrophy is known to occur. Myocardial capillary surface and volume densities and the left ventricular ENDO‐EPI‐gradient in surface density were similar to untreated SHR. However, felodipine‐treatment increased right ventricular weight and capillary volume density.Functional capillary exchange was estimated in terms of permeability surface area products (PS) for Cr‐EDTA and vitamin B12 and normalized for organ weight. PScr‐EDTA, PSB12 and the ratio PScr‐EDTA/PSB12 (an index of capillary permeability) were similar in SHR and WKY. Furthermore, the relation between functional and stereological indices of exchange capacity was investigated in a multiple linear regression analysis. However, no significant correlation between PS and neither capillary surface nor volume density was found.In conclusion, myocardial capillary exchange capacity was well adapted to the pressure overload cardiac hypertrophy present in female SHR. Despite induction of right ventricular hypertrophy, felodipine‐treatment did not affect capillary exchange capacity. Furthermore, when functional and stereologic estimates were performed in parallel, the importance of dynamic factors for myocardial capillary exchange capacity (e.g. heterogeneity) was illustrated.
Effects, release and disposal of endothelin‐1 in conscious dogs
Authors: EMMELUTH C. , BIE P. 
Published: December 2008

Cardiovascular and renal responses to a step‐up infusion of endothelin‐1 (ET‐1) (1, 5, and 15 ng kg‐1 min‐1) were investigated in conscious dogs. In addition, the disappearance of ET‐l in arterial and central venous plasma after an infusion of 10 ng kg‐1 min‐1 was quantified, and the effects of vasopressin (AVP, 10 ng kg‐1 min‐1) and angiotensin II (AII, 2, 5, and 10 ng kg‐1 min‐1) on plasma ET‐1 were investigated. The step‐up infusion of ET‐1 increased the plasma level from 3.6 ± 0.3 to 243 ± 23 pg ml‐1. Concomitantly, arterial blood pressure increased and heart rate (HR) decreased dose‐dependently. Diuresis, sodium, and potassium excretion did not change significantly. However, free water clearance increased during the infusion. Clearance of creatinine and excretion of urea decreased (39 ± 4 to 29 ± 3 ml min‐1 and 87 ± 16 to 71 ± 14 μmol min‐1, respectively). Decay curves for ET‐1 in venous and arterial plasma were identical, and initial t½ was 1.1 ± 0.1 min. Vasopressin increased arterial blood pressure (107 ± 4 to 136 ± 3 mmHg) beyond the infusion period and increased plasma ET‐1 (85%). An equipressor dose of AII tended to decrease plasma ET‐1.It is concluded that the lung is apparently not important in the removal of ET‐1, that the disappearance of ET‐1 follows a complex pattern, and vasopressin – in contrast to angiotensin II – is able to increase the plasma concentration of ET‐1. The latter may suggest that ET‐1 is involved in the prolonged pressor action of AVP observed.
Luminal and basolateral uptake and degradation of insulin in the proximal tubules of the dog kidney
Authors: HYSING J. , ØSTENSEN J. , TOLLESHAUG H. , ANDERSEN K.J. , KIIL F. 
Published: December 2008

In order to determine the major routes of insulin degradation in the body, insulin was labelled with a ‘trapped’ or ‘residualizing’ label: [125I]tyramine‐cellobiose ([125I]TC) and injected intravenously in dogs. In contrast to conventional iodine‐labelled insulin (131I‐insulin), the [125I]TC‐insulin allows measurements of total uptake in specific organs in vivo because the radioactive degradation products do not leave the cells. One h after the injection of trace doses, the amount of radioactivity recovered in the kidney from [125I]TC‐insulin was nine times higher than when conventional [131I]insulin was used. In the blood, the amount of acid‐precipitable radioactivity was the same for both labelled preparations, indicating similar clearance rates.A comparison of the uptake of insulin in filtering vs. non‐filtering (ureter‐occluded) kidneys indicated that the uptake of insulin is twice as high through the luminal than through the basolateral cell membrane; after 60 min, 8.9 ± 0.8% of the injected [125I]TC‐insulin dose remained in the filtering kidney and 3.2 ± 0.2% of the dose was accumulated in the contralateral kidney, with occluded ureter but normal blood perfusion.In both filtering and non‐filtering (ureter‐occluded) kidneys, the subcellular distributions of [125I]TC‐insulin were studied after various times by isopycnic sedimentation in sucrose gradients. No difference between peritubular and tubular uptake was discernible. The intracellular transport was rapid, leading to accumulation of radioactive label in dense lysosomes within 10 min.