摘要:

The purpose of this study was to evaluate the effects of short‐term sympathetic inhibition with clonidine on blood pressure and renal responses to central hypervolaemia induced by thermoneutral head‐out water immersion. Eleven healthy subjects were randomly studied on two occasions, during a 1 h pre‐immersion period, 2 h of water immersion and a 1 h post‐immersion period, after either placebo or clonidine treatment. Clonidine caused a significant suppression of plasma adrenaline, plasma noradrenaline, urinary noradrenaline excretion and mean arterial blood pressure. Blood pressure remained constant during water immersion after both placebo and clonidine, compared with the respective pre‐immersion control values. The suppression pattern of plasma catecholamines and urinary noradrenaline in response to water immersion during placebo was similar after clonidine treatment. Renal volume excretion was not affected by clonidine. In contrast, clonidine caused a significant attenuation of the immersion‐induced stimulation of natriuresis (maximum ‐33±12%,P<0.01, compared with placebo). These data indicate that the renal capacity to excrete sodium is impaired during moderate blood pressure reduction by short‐term sympathetic inhibition with clonidine, whereas the regulation of arterial blood pressure in response to central hypervolaem

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.433146000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Elevation of an organ above the heart reduces the arterial and venous hydrostatic pressures in proportion to the height of elevation. Intact autoregulation protects organs, such as the brain and skeletal muscle, from significant alterations in blood flow and hydrostatic capillary pressure due to the decrease in arterial inflow pressure during such a manoeuvre. However, the consequences of the decreased hydrostatic pressure on the venous side are far from clarified.The present study analyses the local haemodynamic effects of the decrease in arterial and venous hydrostatic pressures that occur during vertical elevation of an organ above the heart at atmospheric and raised tissue pressures (0, 10 and 30 mmHg). A sympathectomized cat skeletal muscle enclosed in a plethysmograph and perfused from the animal was used as the experimental model.The results show that elevation of the muscle above the heart at atmospheric tissue pressure created a variable vascular resistance starting at the venous outlet of the organ, and related to the difference between tissue pressure and venous outflow pressure. This resistance completely protects the organ from the hydrostatic pressure alterations on the venous side. The results also show that arterial pressure variations will exert the same haemodynamic influences on the organ as tissue pressure variations, except for the formation of the venous outflow resistance at raised tissue pressure.The application of these results to normal and injured organs, e.g. normal and injured skeletal muscle and brain, with various tissue pressures, is discussed.

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.444165000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The C‐peptide has recently been suggested to have beneficial effects in several organs and improve glycaemic control in human type I diabetes, while there were no such effects in healthy controls. The exact mechanisms behind these effects are, however, not clear. In an attempt to study the actions of C‐peptide on the microvasculature in normal rats during more controlled conditions, isolated rat hindquarters and kidneys were perfused with albumin solutions in order to obtain low basal concentrations of C‐peptide. In rat hindquarters, infusion of C‐peptide significantly increased the capillary filtration coefficients (CFC) from 0.035±0.002 to 0.044±0.002 mL min‐1100 g‐1mmHg‐1(P<0.001,n=9) and the permeability surface area product (PS) for vitamin B12from 3.48±0.29 to 4.02±0.37 mL min‐1100 g‐1(P<0.01, n=6). Addition of C‐peptide to the perfusate during infusion of sodium nitroprusside did not induce any additional alteration of CFC or PS. The vascular resistance was slightly decreased from 2.74±0.17 to 2.64±0.17 mmHg min 100 g mL‐1(P<0.01, n=9). These effects of C‐peptide are compatible with increases in capillary surface area without alteration of the permeabilityper se.In isolated rat kidneys perfused at low temperature (8 °C) prepared to inhibit all metabolic processes, C‐peptide induced no changes in glomerular filtration rate, total vascular resistance or fractional albumin clearance. Therefore, C‐peptide causes active vasodilation of the normothermic microvasculature and hence recruitment of capillaries. These findings support the previous observations in man that C‐p

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.426147000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The threshold for activation of the humoral renal antihypertensive system, presumably residing in the renomedullary interstitial cells (RIC), is substantially reset upwards in the spontaneously hypertensive rat (SHR). Depressor reactions, normally elicited by an increased renal perfusion pressure, can be inhibited either by high frequency renal nerve stimulation or blockade of nitric oxide synthesis, i.e. manoeuvres decreasing renal blood flow at this high perfusion pressure. The present study was designed to explore the effects on regional renal haemodynamics of blocking NO synthesis withN‐ω‐nitro‐l‐arginine (l‐NNA) in chloralose anaesthetized SHR and Wistar rats. Mean arterial blood pressure (MAP), heart rate (HR), renal blood flow (RBF), cortical blood perfusion (CBP) and papillary blood perfusion (PBP) were measured in renally innervated and denervated SHR (Sin=8, Sdn=8) and in Wistar rats (Win=10, Wdn=10). An innervated non‐treated Wistar group served as control (Cin=12). The laser Doppler technique was used to record CBP and PBP. MAP increased in all groups receivingl‐NNA while HR, RBF and CBP simultaneously decreased. The relative decreases in RBF were more marked into the two SHR groups than in the corresponding Wistar groups. Afterl‐NNA PBP also decreased in all four groups despite the increased MAP and more so in the Sigroup; Wi‐19±8 (P<0.05), Wd‐17±6 (P=0.07), Si‐50±9 (P<0.01) and Sd‐25±9% (P<0.05). We conclude that NO is important for maintaining PBP especially in SHR. The more marked decrease in PBP in the innervated SHR suggests a NO/renal nerve interaction in the control of renomedullary blood flow in SHR. This finding may be of importance for the regulation of the humor

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.429150000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The protective effect ofl‐arginine on ischaemia/reperfusion‐induced myocardial injury was investigated in the rat isolated Langendorff perfused heart. Six groups of hearts subjected to 30 min global ischaemia and 30 min reperfusion received either vehicle,d‐arginine,l‐arginine, the nitric oxide (NO)‐donorS‐Nitroso‐N‐Acetyl‐d, l‐Penicillamine (SNAP), the inhibitor of NO formationNG‐nitro‐l‐arginine (l‐NNA), orl‐arginine plusl‐NNA. The recoveries of left ventricular double product and coronary flow at the end of reperfusion were significantly higher in thel‐arginine group (85±5 and 75±6%, respectively) than in the vehicle group (37±6 and 34±5%, respectively,P<0.05). During both the ischaemic and reperfusion periods, left ventricular end diastolic pressure was lower in thel‐arginine group than in the vehicle group. Creatine kinase outflow and the area of no‐reflow were smaller in thel‐arginine treated hearts (P<0.01). There were no differences between vehicle andd‐arginine treated groups.l‐NNA did not affect recoveryper sebut abolished the protective actions ofl‐arginine. SNAP produced the same protective effects asl‐arginine. Acetylcholine‐induced endothelium‐dependent vasodilation was reduced after ischaemia and reperfusion in the vehicle group but not in thel‐arginine group. It is concluded thatl‐arginine reduces ischaemia/reperfusion‐induced myocardial and endothelial injury. The results suggest that the beneficial effects ofl

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.432152000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Experiments were made on preparations of the rabbit right atrium maintained at 37 °C in oxygenated Krebs–Henseleit solution. Baseline diastolic transmural pressure was held at 2 mmHg. A step increase in diastolic pressure was accompanied by an immediate and rapid increase in atrial rate (fast response), followed by a slower increase (t1/2∼0.5 min) (slow response). The slow response to pressure steps was graded, approaching a maximum increase after a 12 mmHg step (44±4 min‐1from a baseline of 196±5 min‐1; mean±SEM;n=7;P<0.01). In preparations where baseline atrial rate had been reduced 50% by application of carbamylcholine, the slow response to an increase in pressure was augmented (n=7;P<0.01); an increase of 55±9 min‐1for a 12 mmHg step in atrial pressure. In preparations where baseline rate had been increased 63% by the application of isoprenaline, the slow response was attenuated (n=5,P<0.01), an increase of 22±7 min‐1for a 12 mmHg step. During sinusoidal pressure forcing (0.002–1.0 Hz), rate responses of control and carbamylcholine‐treated preparations had a high gain at frequencies 0.02 Hz. Carbamylcholine‐treated preparations also showed a high gain at frequencies 0.2 Hz. There appear to be two distinct intrinsic responses to changes in right atrial pressure; a rapid response which is augmented by cholinergic stimulation, and a slower response which is augmented by cholinergic stimulation and reduced by

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.430151000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

The impact ofin vivoischaemia and ischaemia‐reperfusion (I‐R) on mitochondrial respiratory function was investigated in hypertrophied (HP) hearts with aortic constriction compared with control hearts using an open‐chest rat surgical model. Moreover, mitochondrial susceptibility to superoxide radicals (O2P‐)in vitrowas examined in HP and control hearts with or without I‐R. With the site I substrates pyruvate‐malate, mitochondrial state 4 (basal) respiration and the respiratory control index (RCI) were not affected by either ischaemia alone or I‐R in both HP and control hearts. State 3 (ADP‐stimulated) respiration was increased with I‐R in control hearts, but showed a reduction after I‐R in the HP hearts. Exposure of mitochondria to O2P‐(20 nmhypoxanthine in the presence of 0.13 unit mL‐1xanthine oxidase) significantly increased state 4 respiration, whereas state 3 respiration and RCI were decreased in all treatment groups. I‐R hearts in both HP and control showed greater increases in state 4 respiration with O2P‐than either sham or ischaemic hearts. HP hearts exhibited a significantly lesser extent of inhibition in state 3 respiration and RCI by O2P‐compared with control hearts. These changes in mitochondrial respiratory properties were not observed with the site II substrate succinate. Myocardial reduced vs. oxidized glutathione ratio was significantly decreased after I‐R in both control and HP hearts. Malondialdehyde content showed an increase with I‐R, but the increase was significant only in control hearts. These data indicate that short‐termin vivoI‐R does not impair heart mitochondrial respiratory function, but renders the organelles more vulnerable to imposed oxidative stress. Mitochondria from the HP hearts are more resistant to free radical damage under normal and ischaemic conditions; however, this advantage is s

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.427148000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Chemical renal medullectomy with 2‐bromo‐ethylamine hydrobromide (BEA) has been used to study the importance of the renal medulla in blood pressure regulation. However, conclusive evidence as to whether BEA treatment affects the glomerular barrier is lacking. In the present study, the effects of BEA upon glomerular permselectivity for albumin were studied using isolated kidneys (IPK) perfused at a low temperature (8 °C) to inhibit tubular reabsorption of proteins. Sixteen WKY rats (WB) received an i.v. injection of BEA (150 mg kg‐1) while 10 rats served as controls (WC). Volume balance, urinary osmolality and creatinine clearance (GFR) were measured in metabolic cages. Acute paired experiments (n=9) were performed 5–7 weeks after BEA. The rats were anaesthetized and the totalin vivoalbumin excretion was recorded. The kidneys were then isolated and perfused for measurements of inulin clearance (GFR) and fractional albumin clearance without tubular reabsorption of protein. The nine BEA treated rats showed polyuria and hypoosmotic urine.In vivoGFR was lower in the BEA treated groups when measured with creatinine clearance (459±22 vs. 213±41 μL min‐1100 g‐1body wt,P<0.001), while GFR was not significantly changed in the IPK (WC=135±27, WB=92±14 μL min‐1100 g‐1body wt, n.s.) when perfused at identical pressures. The fractional albumin clearance was increased three times in the BEA group (WB=9.6±3.4J,P<0.05). Moreover, albumin excretionin vivowas similar in the two groups despite low GFR in the BEA group. We conclude that BEA treatment affects glomerular perm

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.435160000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

A change of interstitial fluid volume (IFV) will normally change the interstitial fluid pressure (Pif) so as to counteract further fluid movement across the capillaries and changes in IFV. Contrary to this, several acute inflammatory reactions in the trachea are associated with increased negativity ofPif, which will interstitial fluid balance in the trachea, interstitial compliance (ΔIFV/ΔPif) was measured in pentobarbital anaesthetized rats. IFV was measured as the plasma equivalent extravascular distribution space of [51Cr]EDTA.Pifwas measured in the same animal with sharpened glass pipettes (diameter 3–6 μm) connected to a servocontrolled counterpressure system. In dehydration (30 mL saline i.v.,n=10) interstitial compliance was 0.083 mL g dry wt‐1mmHg‐1. Since control IFV was 1.046 mL g dry wt‐1(n=10) the interstitial compliance is 8% of IFV per mmHg. In overhydration (30 mL NaCl,n=10) and dextran anaphylaxis (1 mL dextran 70,n=10) compliance remained the same for the first 15% increase in IFV and then increased several‐fold sincePifdid not increase more than 2 mmHg above control level. The increased negativity ofPifby ‐10 mmHg associated with acute inflammation will require a reduction of IFV by 80% when interstitial compliance is 8% per mmHg. A more likely explanation is therefore that structural rearrangements are responsible for the events leading to increased negativity ofPifin acut

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.439161000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY

摘要:

Rats pretreated with atropine and adrenoceptor antagonists show secretion of saliva upon electrical stimulation of the parasympathetic nerve of the parotid gland. The protein composition of this secretion has been analysed by sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS–PAGE) and compared with the protein profiles obtained with secretions evoked by parasympathetic stimulation (in the absence of atropine) or infusion of bethanechol with or without vasoactive intestinal peptide (VIP, a probable transmitter conveying parasympathetic secretory impulses). The SDS–PAGE patterns were highly reproducible for an individual rat although minor differences were detected between different rats. The method requires only microlitre volumes of unconcentrated rat saliva and thus is ideal for monitoring sequential aliquots collected from the same rat. The SDS–PAGE patterns indicated (i) little change in the protein profile during prolonged stimulation, (ii) a similar profile with parasympathetic stimulation or infusion of bethanechol, and (iii) a quantitative, rather than qualitative, response to administration of atropine (during parasympathetic stimulation) or VIP (during bethanechol infusion). Thus, the salivary protein composition associated with non‐adrenergic, non‐cholinergic (NANC) secretion appears similar to that evoked in response to parasympathetic nerve stimulation in the absence of muscarinic recept

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1996.428149000.x

出版商:Blackwell Science Ltd    

年代:1996

数据来源: WILEY