摘要:

Adenosine, an endogenous vasodilator, induces a cerebral vasodilation at hypotensive infusion rates in anaesthetized humans. At lower doses (15O]butanol as tracer in four of the subject at another occasion. During normoventilation (5.4 ± 0.2 kPa, mean ± s.e.m.), the cerebral blood flow measured by magnetic resonance imaging technique, as the sum of the flows in both carotid and vertebral arteries, was 863 ± 66 mL min−1, equivalent to about 64 ± 5 mL 100 g−1 min−1. The cerebral blood flow measured by positron emmission tomography technique, was 59 ± 4 mL 100 g−1 min−1. All subjects had a normal CO2reactivity. When adenosine was infused (84 ± 7 μg kg−1 min−1) the cerebral blood flow, measured by magnetic resonance imaging was 60 ± 5 mL 100 g−1 min−1. The end tidal CO2level was slightly lower (0.2 ± 0.1 kPa) during adenosine infusion than during normoventilation. In the subgroup there was no difference in cerebral blood flow as measured by magnetic resonance imaging or positron emission tomography. In conclusion, adenosine infusion at tolerable doses in healthy volunteers doe

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00113.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

In brain cortex all capillaries are perfused with plasma at anyone time while the flow of blood cells is heterogenous. Increased blood flow is associated with increased number of moving erythrocytes in the microcirculation, while capillary recruitment in its classical anatomical sense appears not to exist in the brain. Modulation of the concentration of flowing erythrocytes may influence the oxygen supply to the tissue. Therefore, we examined the possibility that laser‐Doppler flowmetry (LDF) could be used to quantify changes in the microvascular concentration of moving blood cells (CMBC) and blood cell velocity () by comparing LDF measurements with electromagnetic flow measurementsin vitro, and confocal laser‐scanning microscopyin vivoin the brain of anaesthetized male Wistar rats.In vitromeasurements showed that CMBC was affected by changes in haematocrit, whilecorrelated almost linearly with blood cell velocity measured electromagnetically within a relevant physiological range.In vivostudies during hypercapnia (Paco2from 39 ± 4 to 66 ± 5 mmHg) with confocal laser scanning microscopy disclosed a 39 ± 10% increase of cortical capillary erythrocytes, while CMBC measured with LDF increased by 37 ± 5%. Erythrocyte flow velocity in brain cortex capillaries increased by 65 ± 17% with confocal microscopy as compared to 72 ± 8% with LDF. Local electrical stimulation of cerebellar cortex, and application of adenosine or sodium‐nitroprusside, increased CMBC andsimultaneously, while during hypercapnia theincrease preceded the CMBC increase by 30 s. The CMBC rise rapidly reached a steady state in response to all types of stimulation, whilecontinued to increase during the major part, or the entire stimulation period. In conclusion, our data support the hypothesis that LDF may b

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00130.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

We have set up a telemetry system and recorded heart rate, electrocardiogram (ECG), body temperature and the locomotor activity in awake freely moving mice. The telemetry system (DATA Sciences, St Paul, MN, USA) comprises a transmitter implanted in the peritoneal cavity and a receiver (RA1010) placed underneath the home cage. The signal from the transmitter includes the electrical activity of the heart and the body temperature. The results show that four days after the surgical procedure the mice have recovered and regained a clear circadian rhythm. The heart rate varied under baseline conditions between 432 and 618 beats min−1and the body temperature between 35.1 and 37.7 °C (based on 60 min mean values). A clear time correlation between heart rate, body temperature and locomotor activity was found. As an evaluation of the method we injected T3 s.c. during a period of 4 days. Further, we were interested in whether it was possible to measure an integrated physiological response to T3and further investigate the time course for the effect. After one day of treatment with triiodothyronine there was a significant increase in body temperature and locomotor activity. The increase in heart rate was seen after 2 days. The ECG recording revealed a significantly shortened QTend‐ and QRS‐time. No significant difference in the PQ‐time was found. This method may be of great importance in studies of genetically ma

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00134.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The effect of rigorous swim training (6 h day−1, 5 days week−1for an average of 191 h) on mitochondrial respiratory function was investigated in rat heart subjected toin vivoischaemia reperfusion (I‐R). Mitochondria was isolated from the risk region of the left ventricle subjected to 60 min occlusion of the main left coronary artery followed by 30 min reperfusion. Heart weight and heart‐to‐body weight ratio was increased by 21 and 28% (P < 0.01), respectively, in the trained (T, n = 15) vs. control rats (C,n = 20). I‐Rper seshowed minimal effect on heart mitochondria regardless of training status. In sham, state 4 respiration rate was 26 and 32% (P < 0.05) lower in T vs. C rats, using malate‐pyruvate (M‐P) and 2‐oxoglutarate (OG) as substrates, respectively. Training also reduced state 3 respiration by 28% (M‐P) and 50% (OG) (P < 0.01). The respiratory control index (RCI) was unaltered in T with M‐P, but decreased with OG (P < 0.01).In vitroexposure to superoxide radicals severely reduced state 4 and 3 respiration and RCI, but T hearts showed greater reductions of state 4 and 3 rates than C. Mitochondria from T hearts also revealed a greater state 4 inhibition by H2O2and HO•compared with C. A lower glutathione content and a higher γ‐glutamyl transpeptidase activity (P < 0.05) was observed in T vs. C. It is concluded that rigorous swim training impairs heart mitochondrial function, making them more susceptible toin vivoandin vitrooxidative stress, and that this da

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00138.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The effect of different rates of fluid ingestion on heart rate, rectal temperature, plasma electrolytes, hormones and performance was examined during prolonged strenuous exercise conducted at 21 °C. Seven well‐trained males (24 ± 1 yr; 68.6 ± 2.9 kg;Vo2peak = 4.69 ± 0.17 L min−1; mean ± SEM) cycled for 2 h at 69 ± 1%Vo2peak while receiving either no fluid replacement (NF), a volume of water estimated to prevent body weight loss (FR‐100 = 2.32 ± 0.10 L 2 h−1) or 50% of this volume (FR‐50 = 1.16 ± 0.05 L 2 h−1). The 2‐h exercise bout was followed by a ride to exhaustion at a workload estimated to be 90%Vo2peak. After 2 h of exercise, NF was associated with a 3.2 ± 0.1% weight loss, while FR‐50 and FR‐100 resulted in losses of 1.8 ± 0.1 and 0.1 ± 0.1%, respectively. Compared with FR‐100, heart rate and rectal temperature were elevated (P < 0.05) during the second hour of exercise in NF, with FR‐50 intermediate. Reductions in plasma volume during exercise were greater in NF and FR‐50, compared with FR‐100 and plasma sodium concentration was elevated in NF, decreased slightly in FR‐100, with FR‐50 intermediate. Plasma renin activity, aldosterone and atrial natriuretic peptide increased to similar extents in the three trials. Plasma vasopressin remained unchanged for FR‐100, increased for NF, with intermediate values for FR‐50. Exercise time to exhaustion at 90%Vo2peak was longer in FR‐100 (328 ± 93 s) than NF (171 ± 75 s) with FR‐50 (248 ± 107 s) not significantly different from either FR‐100 or NF. In conclusion, the responses of heart rate, rectal temperature, plasma sodium, and vasopressin during,

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00139.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

Previous studies have shown that an oral sodium load during sodium deprivation is excreted faster than an intravenous load. We wanted to study whether the renin‐angiotensin‐aldosterone system might be associated with this phenomenon and therefore the influence of the angiotensin converting enzyme (ACE) inhibitor enalapril was investigated. The experiments were performed on four strains of rat: spontaneously hypertensive rats (SHR), Wistar‐Kyoto (WKY) rats, inbred hypertension‐prone (SS/Jr) and hypertension‐resistant (SR/Jr) Dahl rats. In SHR and WKY rats pretreated with enalapril it was observed that an intravenous sodium load induced a renal sodium excretion which was between two and five times larger than that seen after an oral load. In SR/Jr and SS/Jr rats the sodium excretion was the same regardless of the route of administration. In SS/Jr rats sodium excretion increased three‐ to fourfold upon sodium repletion, whereas no significant increase was observed in SR/Jr rats. Thus, the present results indicate that an intact renin‐angiotensin system is necessary for the interplay between the gastrointestinal tra

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00135.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The influence of repeated administration of angiotensin II (AII) on smooth muscle calcium concentration ([ Ca2+]i) was studied in isolated rabbit renal afferent arterioles loaded with the calcium‐sensitive fluorescent probe Fura–2. [Ca2+]iwas evaluated in the proximal and distal parts of the afferent arterioles. AII (10−8m) increased the [Ca2+]iin both these regions. A second administration of AII, however, did not elicit any response in [Ca2+]i. The response to noradrenaline administration at the end of the experiment was not affected, i.e. there was no fading or cross‐desensitization. Since this desensitization was specific for AII, it was of the tachyphylaxis type. Increasing doses of AII (10−11–10−8m) did not reverse the tachyphylaxis. However, in the proximal part, pretreatment with the voltage‐sensitive calcium channel blocker nifedipine (10−6m) blunted the tachyphylactic effect of a second administration of AII. Whenl‐arginine (l‐Arg) was administered to the bath solution, thus activating the NO system, the development of tachyphylaxis was suppressed in the proximal region. Pretreatment with the protein kinase C (PKC) inhibitor chelerythrine (10‐6m) did not affect the tachyphylaxis. We conclude that the calcium response to AII in the isolated rabbit afferent arteriole shows tachyphylaxis. This tachyphylaxis cannot be reversed by applying increasing doses of AII (10−11–10−8m). PKC does not seem to be involved in the tachyphylactic phenomenon in this preparation. It was also found that nifedipine and

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00153.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

摘要:

The background of the bioelectric activity of muscle recorded from the surface of the skin (surface electromyography) in terms of the representation of single motor units of the underlying muscle(s) is not very well documented or understood. An insight into the composition of an electromyogram is essential for the proper interpretation of one of the most widely applied electrophysiological techniques. In the present paper, a study of the contribution of single motor unit potentials to the surface electromyogram is presented. To this end, the decline of different components of the motor unit potential with depth of the motor unit is quantified. Experimentally, the action potentials from motor units at several positions in the muscle were recorded by 30 skin surface electrodes. Simultaneous use of scanning electromyography provided information about the actual position and size of the motor unit. Observed linear log–log relationships between motor unit potential magnitudes and distance indicated the usefulness of a power function to describe the motor unit potential's dependence on recording distance. It is shown that different specific surface motor unit potential characteristics fall off differently with depth. The magnitude–distance relationship is shown to be dependent on the recording configuration (unipolar vs. bipolar recording, including the inter‐electrode distance) and the chosen motor unit potential parameter (negative peak amplitude, positive peak amplitude and

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00152.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.00156.x

出版商:Blackwell Science Ltd.    

年代:1997

数据来源: WILEY