摘要:

The effects of focal activation of serotonergic receptors in motorneurones were investigated in a slice preparation of the turtle spinal cord. The test response to glutamate evoked from a dendrite by iontophoresis was attenuated by serotonin or 8‐hydroxy‐dipropyl‐aminotetralin (8‐OH‐DPAT) applied from an independent pipette within 100 μm of the glutamate pipette. This effect was not associated with a conductance change and did not affect glutamate responses evoked more than 100 μm from the serotonin pipette. The effect of serotonin was not reproduced by H+ions. Plateau potentials were rarely facilitated by serotonin when applied in the dendritic field. Plateau potentials were readily facilitated by serotonin applied near the soma. This effect was preceded by attenuation of the slow after‐hyperpolarization following an action potential. Applied near the soma, serotonin inhibited the response to a depolarizing current pulse of moderate strength and enhanced the response to a current pulse of high amplitude. These effects were associated with a conductance increase. We conclude that serotonin has spatially diverse effects on

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.558326000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

摘要:

Local actions of acetylcholine on vasomotor regulation in rat incisor pulp were investigated in anaesthetized animals. Pulpal blood flow was measured with laser Doppler flowmetry. Iontophoresis (40 or 60 μA for 20 s) with acetylcholine or carbachol on an exposed dentin surface caused a biphasic response: an initial vasoconstriction was followed by an atropine‐sensitive vasodilation. The vasoconstrictor response was enhanced by 171% in the presence of atropine, whereas in control experiments, using isotonic saline as a medium for the direct current, similar vasoconstriction was unaffected by atropine. Carbachol‐induced vasodilation was significantly reduced by 30% after intravenous injection of the nitric oxide synthesis blockerNωw‐nitro‐L‐arginine methyl ester (10 mg kg‐1), and the remaining vasodilation was abolished by atropine. The present results support the concept of a cholinergic modulation of sympathetic vasoconstrictor function and of a partial contribution of nitric oxide in carbachol‐induced vasodilation in r

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.69319000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

摘要:

Hypocapnia is known to have an antiphosphaturic effect that overcomes the phosphaturic effect of hypoxia. The objective of this study was to examine whether conscious rats exposed to acute hypoxia show a decrease in phosphate excretion due to the concomitant hypocapnia. Wistar rats weighing 200 g were exposed to hypoxia (inspired oxygen fraction=0.10) or normoxia (inspired oxygen fraction=0.21) for 6 h; and rats were alternately exposed to hypoxia or normoxia every 12 h for a total 36 h. Renal clearance and hormone studies were performed. Rats exposed to 6 h of hypoxia (n= 11) showed significant hypophosphaturia and decreases in absolute and fractional excretion of phosphate (0.38±0.10 μg min‐1, mean ±SE,P<0.0001 and 0.59±0.15%,P<0.0001) as compared with normoxic rats (n= 11, 3.91±0.68 μg min‐1and 5.62±0.85%). In addition, nephrogenous adenosine 3′,5′‐cyclic monophosphate level per glomerular filtrate was significantly decreased (‐0.87±0.64 nmol dL GF‐1,P<0.05) and plasma parathyroid hormone level was unchanged (45.2±9.5 pg mL‐1) after 6 h of hypoxia as compared with normoxic rats (4.03±1.83 nmol dL GF‐1and 54.3±10.4 pg mL‐1). A parallel increase in urinary noradrenaline and a decrease in dopamine excretion was observed in rats after 6 h of hypoxia. The decreased phosphate and adenosine 3′,5′‐cyclic monophosphate excretion during acute hypoxia were restored to normoxic levels by reoxygenation with 21% oxygen in the study of 12‐h intermittent hypoxia. In summary, (1) hypoxia produced by inhalation of 10% oxygen for 12 h or less causes reduced phosphate and adenosine 3′,5′‐cyclic monophosphate (cAMP) excretion by spontaneously breathing rats; (2) these effects are reversed by reoxygenation and (3) hypoxia elicits a parallel increase in noradrenaline excretion and a decrease in dopamine excretion. These data suggest that renal adrenergic and dopaminergic systems play important roles in hypophospha

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.555318000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

摘要:

Performance of intense dynamic exercise in highly trained athletes is associated with a reduced arterial haemoglobin saturation for O2(SaO2) and lower arterialPO2(PaO2). We hypothesized that compared with upright exercise, supine exercise would be accompanied by a smaller reduction inSaO2because of a lower maximal O2uptake (VPO2max) and/or a more even ventilation–perfusion distribution. Eight elite bicyclists completed progressive cycle ergometry to exhaustion in both positions with concomitant determinations of ventilatory data, arterial blood gases and pH. During upright cyclingVPO2maxaveraged 75±1.6 mL O2min‐1kg‐1(±SEM) and it was 10.6±1.7% lower during supine cycling (P<0.001). Also the maximal pulmonary and alveolar ventilation were lower during supine cycling (by 15±2% and 21±3%, respectively;P<0.001) which related to a 0.8±0.1 L lower tidal volume (P<0.001). In all subjects and independent of work posturePaO2andSaO2decreased from rest to exhaustion (from 99±3 to 82±2 Torr and 98.1±0.2 to 95.2±0.4%, respectively;P<0.001); alveolar–arterialPO2difference increased from 6±2 to 37±3 Torr in both body positions. At exhaustion arterialPCO2was lower in upright than in supine (33.4±0.6 vs. 35.9±0.9 Torr;P<0.01), suggesting a greater relative hyperventilation in upright. Arterial pH was similar in upright and supine at rest (both 7.41±0.01) and at exhaustion (7.31±0.01 vs. 7.32±0.01, respectively). We conclude that despite a lowerVPO2maxand supposedly an improved ventilation–perfusion distribution, altering body position from upright to supine does not influence arterial O2desaturati

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.575323000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

摘要:

The aim of the study was to compare breathing pattern, mouth occlusion pressure, mean inspiratory flow and the ratio of mouth occlusion pressure to mean inspiratory flow at the same power output and carbon dioxide output during arm and leg incremental exercise. Mouth occlusion pressure was used as an index of inspiratory neuromuscular activity and its ratio to mean inspiratory flow as an index of the ‘effective’ impedance of the respiratory system. Eight normal subjects performed two incremental exercise tests, one with arms, the other with legs, on different weeks and in randomized order, and on two identical cycle ergometers. The power output was increased by steps of 25 W for arms and 50 W for legs every 4 min until exhaustion. At the same power output, oxygen consumption, carbon dioxide output, ventilation, mean inspiratory flow, mouth occlusion pressure, ‘effective’ impedance (P<0.001) and respiratory frequency (P<0.01) were higher during arm exercise than during leg exercise, whereas inspiratory time (P<0.05) and expiratory time (P<0.01) were lower. At the same carbon dioxide output, mouth occlusion pressure, ventilation, ‘effective’ impedance (P<0.001) and respiratory frequency (P<0.01) were higher and expiratory time (P<0.05) was lower during arm exercise. In conclusion, the higher inspiratory neuromuscular activity and impedance of the respiratory system during arm exercise and the differences observed in ventilation and breathing pattern at equal carbon dioxide output seem related to the differences in exercising muscle afferents and the presence of an increased load due to contraction of rib cage muscles to stabil

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.551317000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

摘要:

The vasodilator gas nitric oxide (NO) is produced in the paranasal sinuses and is excreted continuously into the nasal airways of humans. This NO will normally reach the lungs with inspiration, especially during nasal breathing. We wanted to investigate the possible effects of low‐dose inhalation of NO from the nasal airways on pulmonary function. The effects of nasal and oral breathing on transcutaneous oxygen tension (tcPO2) were studied in healthy subjects. Furthermore, we also investigated whether restoring low‐dose NO inhalation would influence pulmonary vascular resistance index (PVRI) and arterial oxygenation (PaO2) in intubated patients who are deprived of NO produced in the nasal airways. Thus, air derived from the patient's own nose was aspirated and led into the inhalation limb of the ventilator. In six out of eight healthy subjects tcPO2was 10% higher during periods of nasal breathing when compared with periods of oral breathing. In six out of six long‐term intubated patientsPaO2increased by 18% in response to the addition of nasal air samples. PVRI was reduced by 11% in four of 12 short‐term intubated patients when nasal air was added to the inhaled air. The present study demonstrates that tcPO2increases during nasal breathing compared with oral breathing in healthy subjects. Furthermore, in intubated patients, who are deprived of self‐inhalation of endogenous NO,PaO2increases and pulmonary vascular resistance may decrease by adding NO‐containing air, derived from the patient's own nose, to the inspired air. The involvement of self‐inhaled NO in the regulation of pulmonary function may represent a novel physiological principle, namely that of an enzymatically produced airborne messenger. Furthermore, our findings may help to explain one biological role of the human para

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.557321000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

摘要:

During dynamic exercise, mean blood velocity (Vmean) in the middle cerebral artery (MCA) demonstrates a graded increase to work rate and reflects regional cerebral blood flow. At a high work rate, however, vasoactive levels of plasma catecholamines could mediate vasoconstriction of the MCA and thereby elevateVmeanat a given volume flow. To evaluate transcranial Doppler‐determinedVmeanat high plasma catecholamine levels, seven elite cyclists performed a maximal performance test on a bicycle ergometer. Results were compared with those elicited during five incremental exercise bouts and during rhythmic handgrip when plasma catecholamines are low. During rhythmic handgrip theVmeanwas elevated by 21±3% (mean±SE), which was not statistically different from that established during moderate cycling. However, at the highest submaximal and maximal work intensities on the bicycle ergometer,Vmeanincreased by 31±3% and 48±4%, respectively, and this was significantly higher compared to handgrip (P<0.05). During maximal cycling, plasma adrenaline increased from 0.21±0.04 nmol L‐1at rest to 4.18±1.46 nmol L‐1, and noradrenaline increased from 0.79±0.08 to 12.70±1.79 nmol L‐1. These levels were 12‐ to 16‐fold higher than those during rhythmic handgrip (adrenaline: 0.34±0.03 nmol L‐1; noradrenaline: 0.78±0.05 nmol L‐1). The increase inVmeanduring intense ergometer cycling conforms to some middle cerebral artery constriction elicited by plasma catecholamines. Such an influence is unlikely during rhythmic handgrip compared w

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.564325000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

摘要:

The stimulation of transepithelial sodium transport by arginine vasotocin (AVT) and the ability of prostaglandin E2(PGE2) to inhibit the AVT dependent sodium transport was examined on pieces of frog skin taken from different regions of the frog. The basal sodium transport was of the same magnitude in the abdominal, thoracal and upper and lower dorsal region. In all regions the sodium transport could be stimulated by AVT, though the stimulation was highest in the abdomen. Subsequent addition of PGE2caused a significant inhibition of the AVT dependent sodium transport in the abdomen but had only minor effects on the other parts of the skin. Therefore, pieces of skin from the abdomen were selected for the remaining experiments. Addition of PGE2to skin pieces in the presence of AVT resulted in a hyperpolarization of the cellular potential and a decrease in the transepithelial sodium transport, indicating a decreased apical sodium permeability. This was correlated with a decrease in cellular cAMP contents. We conclude that frog skin exhibits large regional differences in sensitivity to AVT and that PGE2only modulates the natriferic effect of AVT in the abdomen.

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.554316000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

摘要:

This project sought to evaluate the importance of skin temperature during heat acclimation, using an isothermal‐strain model. Two groups of seven matched males, participated (1 h per day, 10 days) in one of two conditions: (i) temperate physical training (TEMP: 22.4±0.7 °C, relative humidity (r.h.) 41.0±0.9%); or (ii) combined physical training and heat acclimation (HEAT: 38.2±0.7 °C, r.h. 39.7±1.3%). Isothermal strain was induced in both groups by rapidly elevating rectal temperature by 1 °C (cycling), then holding it constant by manipulating external work. Subjects completed two three‐phase heat stress tests (39.8±0.1 °C, r.h. 38.6±1.2), consisting of 20 min rest, then 20 min cycling at each of 30% and 45% of peak power, before and after each regimen. While there was a difference of 4.2 °C in mean skin temperature between treatments, both regimens elicited a similar peripheral sudomotor increase, indicating a core temperature dependent adaptation. However, based on significant pre‐ vs. post‐acclimation decreases in average auditory canal temperature (0.4±0.1 °C), average forehead skin blood flow (26%), average perceived exertion (11%), and a 5% increase in average forehead sweat rate (0.1±0.04 mg cm−2min−1), the HEAT regimen elicited a more complete acclimation. While elevation in core temperature is critical to acclimation, it also appears necessary to expose subjects to an external thermal stress. This observation has not been previously demonstrated under conditions of isothermal strain, and verifies the importance of skin temperature elevation i

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.561311000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.58340000.x

出版商:Blackwell Science    

年代:1996

数据来源: WILEY