bluuebunny/crossref_metadata_2025_split huggingface dataset:
Respiratory and circulatory responses to sustained positive‐pressure breathing and exercise in man
Authors: Bjurstedt H. , Rosenhamer G. , Lindborg B. , Hesser C. M. 
Published: December 2008

AbstractTo investigate the effects of sustained positive‐pressure breathing (PPB) on the adaptation of respiratory and circulatory functions to exercise, 8 healthy volunteers were exposed to PPB of air at 15 and 30 cm H2O in the supine position at rest and while performing leg exercise at 50% of individual maximal working capacity. PPB was both subjectively and objectively better tolerated when combined with exercise than it was at rest. PPB at 30 cm HaO resulted in marked hyperventilation with alkalosis in the resting condition, but did not significantly affect respiratory minute volume, blood gases or acid‐base balance during exercise. Cardiac output and left ventricular work were reduced by about one fifth and one third, respectively, both at rest and during exercise. In contrast to the case at normal airway pressure, exercise‐induced increase in cardiac output was accompanied by an increment in stroke volume during PPB. Although mean arterial pressure (relative to atmospheric) was elevated by PPB at rest and during exercise, the driving pressure in systemic circuits (arterial minus central venous pressure) was reduced in both conditions. It is concluded that dynamic exercise counteracts deleterious effects of PPB by normalizing respiratory function and by improving cardiac filling by activation of the leg muscle and the abdominal pumps.
Uptake and release of adenosine in isolated rat fat cells
Authors: FREDHOLM BERTIL B. , HJEMDAHL PAUL 
Published: December 2008

AbstractRadioactively labelled adenosine and adenine were rapidly taken up by isolated rat fat cells, and incorporated into nucleotides, of which ATP dominated. The overall process had an apparent Kmof 1–5 μM. During incubation, especially in the presence of lipolytic agents, there was a reduction in labelled ATP with a compensatory increase in ADP, AMP, cAMP and nucleosides. The build‐up of adenosine during incubation was inhibited by theophylline, which inhibits 5′‐nucleotidase. Radioactivity released from perifused fat cells consisted mainly of nucleoside material, of which adenosine predominated. Lipolytic stimulation caused no significant increase in nucleoside outflow from perifused cells, whereas oxygenation was capable of reducing this outflow. It is concluded that adenosine is formed by fat cells as a consequence of ATP breakdown. Stimulation of lipolysis during activation of the sympathetic nerves leads to reversible ATP breakdown and adenosine release. Adenosine might therefore act as a modulator of lipolysisin vivounder these conditions, even though it does not serve as a feed back regulator in the proper sense.
Cardiac receptors with non‐medullated vagal afferents in the rat
Authors: THORÉN PETER , NORESSON EDDY , RICKSTEN SVEN‐ERIK 
Published: December 2008

AbstractThe characteristics of 22 atrial receptors in 15 normotensive adult male Wistar rats were investigated. AH the receptor afferents were included in the C‐fibre group with conduction velocities from 0.4 to 1.2 m/sec. No atrial medullated receptors or ventricular C‐fibre endings were found. Two receptors were located in right atrium and 2 receptors throughout left atrium. Upon elevation of the left atrial pressure the receptor discharge was markedly elevated with thresholds from 2.5 to 9 mmHg in mean left atrial pressure. Ten of the atrial receptors displayed a clear cardiac rhythmicity upon activation and the discharge correlated with the v‐wave, indicating distension as the cause of receptor activation. The maximal firing rate in most receptors was very high (up to 70 Hz), but 8 receptors had maximal firing rates below 25 Hz. These low frequency receptors had higher threshold and showed a more irregular firing. Thus, there is a substantial population of atrial receptors with vagal non‐medullated afferents in the rat heart and the thresholds for many of these receptors are so low that they are likely to be active during normal conditions.
The effect of water temperature on the hormonal response to prolonged swimming
Authors: GALBO H. , HOUSTON M. E. , CHRISTENSEN N. J. , HOLST J. J. , NIELSEN B. , NYGAARD E. , SUZUKI J. 
Published: December 2008

AbstractThe relationship between thermoreception, hormonal secretion and muscular activity was studied. 6 men swam 60 min in 21, 27 and 33°C water at a speed requiring 68 % of Voa max (determined in 27°C water). Rectal temperature increased in 33°C (1.3 ± 0.2°C, mean and S.E.) and 27°C (0.7 ± 0.1°C) expts. but decreased in 21°C expts. (0.8 ± 0.3°C). Changes in esophageal and muscle temperatures parallelled changes in rectal temperature. Plasma noradrenaline was higher in 33°C than in 27°C expts. and growth hormone, Cortisol and glucagon concentrations increased in 27°C and 33°C expts. only. Insulin concentrations were uniformly depressed during swimming at the different water temperatures. In 21°C expts. noradrenaline and adrenaline concentrations were higher than in 27°C expts. VO2, carbohydrate combustion and peak lactate were slightly lower in 33°C expts. Plasma glucose decreased slightly and FFA and glycerol concentrations increased identically in all expts. Heart rate increased continuously during swimming in 27°C and 33°C expts., but not in 21°C expts. In conclusion the rise in body temperatures normally observed during exercise enhances the exercise induced increases in the plasma concentrations of noradrenaline, Cortisol, growth hormone and glucagon. Decreased body temperatures may elicit catecholamine secretion as a direct consequence of thermoreception. Shivering may account for previously observed decreases in insulin secretion during cold stress but not for increases in Cortisol and growth hormone.
The influence of calcium on morphology and histamine content of isolated intact rat mast cell granules
Authors: ANDERSON PER , RÖHLICH PÁL , UVNÄS BÖRJE 
Published: December 2008

AbstractHistamine is released by “sequential exocytosis” in mast cells. The exocytosis involves fusion of the plasma membrane with the perigranular membrane and further fusions of adjacent perigranular membranes. To study a possible direct effect of Ca2+on granule membrane fusions, mast cell granule suspensions were prepared from sonicated rat mast cells. With the sonication method used, more than 60% of the granules obtained were found to be homogeneous, electron dense and surrounded by a perigranular membrane, when observed in the electron microscope. These granules correspond to normal, histamine‐containing granules found in untreated mast cells and are therefore named “intact” granules. The other granules were swollen, less electron dense and without a perigranular membrane. These “changed” granules are formed during the histamine release process. Aliquots of the granule suspension were incubated in 0.34 M sucrose buffered with 10 mM HEPES, pH 7.0, containing different concentrations of CaCl2, MgCl2(10 mM, 1 mM, 100 μM, 10 μM) or NaCl (10 mM). Only with the highest concentration (10 mM) of Ca2+or Mg2+was it possible to visualize an apposition of the perigranular membranes of “intact”, normal granules. No elimination of the individual membrane structures could be observed at the place of membrane contact. Thus, we found no signs of membrane fusions. The histamine content was lower in the suspensions incubated with lower concentrations of these ions or with 10 mM NaCl. Ca2+and Mg2+in high concentrations seemed to stabilize the perigranular membranes instead of initiating histamine release. Therefore, changes in the Ca2+‐ion concentration per se do not explain the membrane fusions seen in mast cells during “sequential exocytosis”.
Fasting and prolonged exercise increase vasoactive intestinal polypeptide (VIP) in plasma
Authors: GALBO H. , HILSTED J. , FAHRENKRUG J. , De MUCKADELL O. B. SCHAFFALITZKY 
Published: December 2008

Abstract6 young men had venous blood drawn during 4 experiments. The concentration of VIP in plasma increased markedly (from 1.8 (0–4.5) to 22.3 (7.8–43.8) pmol‐1−1, mean and range) during 3 h of mild bicycle exercise but not at all during an equivalent period of rest or during short term submaximal and maximal exercise. During 59 h of fasting, VIP increased from 3.6 (0.6‐6.6) to 10.2 (6.6–13.8) pmol‐1−1 (p < 0.05). The concentration of glucose in plasma decreased significantly during the prolonged exercise as well as during fasting. The known metabolic actions of VIP and the demonstrated increases in its plasma concentration during negative energy balance indicate that VIP is “a polypeptide of substrate need”.
Cardiovascular responses during one‐ and two‐legged exercise in middle‐aged men
Authors: MAGNUSSON G. , KAIJSER L. , ISBERG B. , SALTIN B. 
Published: December 2008

Eight healthy and regularly physically active men, 44–69 years old, performed one‐ and two‐legged dynamic knee extension exercise at increasing work intensities, including one leading to exhaustion. Leg blood flow increased linearly in relation to work rate, reaching a peak value of 5.1 ±0.4 1 min‐1. With a mean weight of quadriceps femoris of 2.2 ±0.1 kg, a peak perfusion of 2.3 ±0.11 kg‐1 min‐1 was attained. The maximal leg oxygen uptake was 0.72 ±0.071 min‐1 (0.33 ±0.03 1 kg‐1 min‐1). At submaximal work the elevation in limb oxygen uptake accounted for between 70 and 100% of the rise in pulmonary oxygen uptake. Comparing two‐ with one‐legged knee extension the cardiac output was 1.5 1 min‐1 higher at each work level, reaching 13.7±0.7 and 12.3 ± 1.0, respectively at exhaustion, leaving 3.5 and 7.2 1 min‐1 of blood flow to the remaining body (cardiac output –leg blood flow). The mean arterial pressure was 119 ±5 mmHg at rest and increased to 155 mmHg for both test modes at the maximal work rate. The femoral arterial and venous plasma concentrations of lactate, ammonia and noradrenaline were significantly higher for two‐legged as compared with one‐legged exercise at the maximal load performed. However, the rate of release per leg, for both lactate and ammonia, did not differ between the two test conditions.It is concluded that physically active middle‐aged men, with a well‐retained muscle mass, can maintain a high skeletal muscle perfusion, similar to that of young males. However, the blood flow is achieved with a higher mean arterial pressure and an elevated sympathetic activity, as reflected by noradrenaline in plasma and spillover from the exercising limb.
Cortisone‐induced changes in myosin heavy chain distribution in respiratory and hindlimb muscles
Authors: POLLA B. , BOTTINELLI R. , SANDOLI D. , SARDI C. , REGGIANI C. 
Published: December 2008

In this study the effects of administration of cortisone acetate (100 mg kg‐1 body weight subcutaneously for 11 days) on distribution and cross‐sectional area of different fibre types of rat skeletal muscles were investigated. Diaphragm, parasternal intercostal (PI), extensor digitorum longus (EDL) and soleus muscles were examined in cortisone treated animals (CA) in comparison with ad libitum controls (CTRL) and pair‐fed (PF) controls. Four fibre types (I or slow and IIA, IIX, IIB or fast) were identified on the basis of their myosin heavy chain composition using a set of monoclonal antibodies.In CA rats the reduction of cross‐sectional area was above 30% in IIX fibres of diaphragm, IIB fibres of PI and in all fast fibres of EDL. In all muscles slow fibres were spared from atrophy.Significant variations in fibre type distribution were found in the muscles of CA rats when compared to CTRL. The percentage of IIB fibres decreased in EDL, PI and diaphragm. This decrease was accompanied by an increase in the percentage of IIA fibres in the same muscles. No changes in the percentage of slow fibres and of fast IIX fibres were observed in EDL, PI and diaphragm of CA rats in comparison with CTRL. In soleus of CA rats the proportion of IIA fibres was lower than in CTRL. In EDL of PF rats atrophy of IIA fibres and changes in fibre type distribution were similar to those observed in CA rats. In diaphragm, PI and soleus of PF rats no significant decrease in fibre cross‐sectional area nor significant changes in fibre distribution were found in comparison with CTRL rats.
The role of volume‐sensitive CI channels in the stimulation of chloride absorption by short‐chain fatty acids in the rat colon
Authors: DIENER M. , PETER A. , SCHARRER E. 
Published: December 2008

The short‐chain fatty acids acetate, propionate and butyrate induced a concentration‐dependent decrease in short‐circuit current (Isc) of the rat colonin vitro.The decrease inIsc, being more pronounced in the distal than in the proximal colon, was dependent on the presence of CI‐ions and partly on the presence of HCO‐3. In the distal colon, the fall inIsccould be inhibited by amiloride, indicating that the activity of the Na+/H+exchanger is necessary for the induction of this response. The decrease inIscwas diminished by the CI‐channel blocker, 5‐nitro‐2‐(3‐phenylpropylamino)‐benzoate, and the lipoxygenase inhibitor, nordihydroguaiaretic acid. In contrast, inhibitors of the leukotriene pathway or a CI‐channel blocker did not affect theIscresponse in the proximal colon.Measurements of unidirectional fluxes revealed that butyrate caused a stimulation of the mucosa to serosa fluxes (Jms) of Na+and CI‐in the distal, but only of jmsNain the proximal colon. Unidirectional Rb+fluxes were not altered. The stimulation of jmsclcorrelated with the degree of metabolism of the short‐chain fatty acid. The increase in jmsclwas most pronounced for butyrate, smaller for acetate and not observed with the poorly metabolizable short‐chain fatty acid, isobutyrate. Consequently, two factors seem to be responsible for the stimulation of CI‐absorption by short‐chain fatty acids in the distal colon: (1) the intracellular production of HCO‐3during the oxidation of short‐chain fatty acids as substrate for the apical Cr/HCO‐3exchanger, and (2) the activation of volume‐sensitive basolateral CI‐channels.
Rhythmic contractions of isolated, pressurized small arteries from rat
Authors: GUSTAFSSON H. , BÜLOW A. , NILSSON H. 
Published: December 2008

The present study was undertaken to examine the influence of transmural pressure on vasomotion and to determine if any such influence was endothelium–dependent. Responses to changes in intravascular pressure of cannulated mesenteric small arteries were investigated under no–flow conditions. Both intact and endothelium–denuded arteries dilated passively when intravascular pressure was increased stepwise from 20 to 140 mmHg. When tone was induced by noradrenaline, pressure increase resulted only in dilatation, independent of endothelium. The sensitivity to noradrenaline was significantly increased in vessels without endothelium, indicating a relaxing influence of the endothelium. Rhythmic contractions in response to noradrenaline occurred in all intact arteries, but were absent when the endothelium was removed. The amplitude of the rhythmic contractions decreased significantly when transmural pressure was elevated. The frequency increased when pressure was elevated from 20 to 80 mmHg and then remained rather constant during further pressure increases. As shown previously in non–pressurized arteries, exogenous cyclic GMP induced oscillations in endothelium–denuded arteries. Pressure–related effects on vasomotion were not dependent on an intact endothelium. Ryanodine, ouabain or verapamil inhibited the rhythmic activity, confirming previous results in non–pressurized arteries.Thus, changes in transmural pressure can modulate vasomotion, but this effect does not appear to be mediated by the endothelium. Generation of vasomotion may depend on release of Ca2+ from intracellular stores, the activity of the Na+, K+–pump and transmembrane Ca2+ inflow in a pressurized artery as shown previously in these arteries under isometric conditions.
Effects of NIC, receptor antagonists on vasodilation induced by chemical and electrical activation of sensory C–fibre afferents in different organs
Authors: STJÄRNE P. , RINDER J. , DELAY–GOYET P. 
Published: December 2008

The effects of the non–peptide NK, receptor antagonists, CP96,345 and RP–67,580, were investigated in a model using anaesthetized pigs. Both the blood flow in the internal maxillary and the bronchial artery (ultrasonic flowmetry) and the superficial blood flow in nasal mucosa and the skin (laser–Doppler flowmetry) were monitored simultaneously. Vasodilation induced by substance P administered i.v. systemically was blocked by pretreatment with CP–96,345, 3 mg kg1 but not by RP–67,580. CP–96,345 had no effects on the vasodilationo induced by calcitonin gene–related peptide or vasoactive intestinal polypeptide. The capsaicin–induced vasodilation in the superficial blood flow of the nasal mucosa and the skin, was reduced after the CP–96,345 pretreatment. The vasodilation induced by capsaicin infusion in the internal maxillary or the bronchial artery was not affected by the CP–96,345 pretreatment. Electrical stimulation of the vagal nerve induced a vasodilation in the bronchial circulation which was not attenuated by pretreatment with CP–96,345.In the nasal mucosa and the skin NK1 receptors seem to be involved in the vasodilation in the superficial small vessels, due to chemical activation of sensory C–fibre afferents. Furthermore, CP–96,345 is a useful tool in the evaluation of NKX receptor–mediated responses. RP–67,580 which has been shown to have NK1 antagonistic properties in the rat has no such effects in the domestic pig.
Role of the endothelium in regulation of vascular functions in two teleosts
Authors: SVERDRUP A. , KRUGER P. G. , HELLE K. B. 
Published: December 2008

Functional and structural aspects of the vascular endothelium were studied in major blood vessels from two distantly related species, the Atlantic salmon(S. salar)and the cod (G.morhua.) The ventral aorta (VA) of both teleosts and the dorsal aorta (DA) and the coeliaco mesenteric artery (CMA) of the cod and the salmon respectively were examined for endothelium dependent and independent responses to acetylcholine (ACh), adrenaline (A) and endothelin–1 (ET–1).In the salmon, endothelial probing resulted in reduced contractile responses to high K+in both VA and CMA while the responses to ACh and A were reduced only in CMA. Indomethacin, but not L–NMMA, enhanced vasoconstrictions to high K+, ACh and A in the unprobed CMA.In the cod vessels the endothelial probing caused reduced contractile responsestothe two effective vasoconstrictors in both vessels, to high K+and A in VA and to high K+and ET–1 in DA. Both indomethacin and L–NMMA enhanced contractile tension to A in VA, while indomethacin, but not L–NMMA, enhanced the constrictions by high K+in VA and by ET–1 in DA.These experiments have revealed heterogeneous patterns of endothelial function in blood vessels of two teleosts, reflecting differences in endothelial morphology and in production of potent endothelial derived contracting factors as well as prostanoic and non–prostanoic endothelium–derived dilating factors.
Membrane stretch evoked by cell swelling increases contractile activity in vascular smooth muscle through dihydropyridine‐sensitive pathways
Authors: BÜLOW A. , JOHANSSON B. 
Published: December 2008

Effects of the dihydropyridine calcium antagonist felodipine and of calcium reduction were studied on osmotically induced contractile responses in the vascular smooth muscle of the rat isolated portal vein. Previous studies have shown that changes in osmolarity that cause cell swelling are accompanied by increased contractile activity in this smooth muscle (Johansson & Jonsson 1968). A transient enhancement of the contractile activity developed in the portal vein on return to standard Krebs solution after exposure to 60 mM urea. This osmotic response was dependent on extracellular Ca2+ (abolished in Ca2+ free solution+ 0.1 mM EGTA) and was reduced in proportion to the decrease in spontaneous phasic contractile activity when Ca2+ was lowered from the standard 2.5 mM concentration. Felodipine, 3 nM, reduced the spontaneous activity to approximately 50% but showed an even more pronounced inhibitory effect on the osmotic responses which were reduced to less than 20% of control. Other calcium antagonists such as verapamil, 60 nM and diltiazem, 300 nM, were also more effective in inhibiting the osmotic responses than the spontaneous activity. In contrast, the K+ channel opener, pinacidil, 100–200 nM, reduced the spontaneous activity to 50% but had only minor inhibitory effect on the osmotic responses, about 75% still persisting.It is suggested that stretch of the cell membrane in response to variations in osmolarity induces contractile activity in vascular smooth muscle by mechano‐electrical coupling involving dihydropyridine‐sensitive pathways.
Influence of coronary venous retroinfusion and vasodilatation on regional myocardial blood flow measurement with microspheres. An analysis of ‘microsphere loss’ from ischaemic and reperfused porcine hearts
Authors: HAGA Y. , NORDLANDER R. , SJÖQUIST P.‐O. , RYDÉN L. 
Published: December 2008

The influence of coronary venous retroinfusion and a vasoselective calcium antagonist felodipine on the microsphere loss in a porcine model of myocardial ischaemia and reperfusion was studied.Sixteen open‐chest pigs underwent 45 min of myocardial ischaemia induced by occlusion of the left anterior descending coronary artery followed by 4 h of reperfusion. Either felodipine (felo‐retro group, 7 nmol kg‐1, n= 6) or the corresponding amount of vehicle (vehicle‐retro group, n= 5) was infused retrogradely into the coronary veins over 30 min, starting 5 min before reperfusion. In a third group, the same amount of felodipine was administered intravenously (felo‐iv group, n= 5). Myocardial regional blood flow was measured with radiolabelled microspheres (ø= 15 μm) injected before ischaemia to investigate a possible loss during ischaemia.In the felo‐retro group, the apparent blood flow in the ischaemic areas, expressed as a percentage of the corresponding values in the non‐ischaemic areas (%‐flow), were 73±15, 73±11 and 75±19 in the subendocardial, midmyocardial and subepicardial layers, respectively. The corresponding percentage flows were 64±11, 70±11 and 62±9 in the vehicle‐retro group and 75±18, 77±15 and 76±11 in the felo‐iv group. The differences between the groups were not satistically significant.It is concluded that in this open‐chest preparation microsphere loss observed in the ischaemic and reperfused myocardium is not increased by coronary venous retroinfusion or by a concomitantly administered vasodilative agent like felodipine.