摘要:

1,1‐dimethylguanidine (DMG) is an endogenous nitric oxide (NO) synthesis inhibitor. This study investigates the effects of exogenous DMG administration, in anaesthetized spontaneously hypertensive rats (SHR) and Wistar‐Kyoto rats (WKY). Mean blood pressure (MBP), heart rate (HR) and renal sympathetic nerve activity (SNA) were recorded in 12‐ to 14‐week old, anaesthetized SHR and WKY. Each rat received increasing bolus injections of DMG intravenously (1.03, 2.05, 6.39, 20.45 and 51.15 mg kg‐1). In separate experiments, SHR receivedL‐arginine orD‐arginine in a dose of 300 mg kg‐1followed by DMG at 6.39 mg kg‐1. Thirty minutes later they received the same doses of the respective arginines followed by DMG at 20.45 mg kg‐1. DMG induced dose‐dependant increases in MBP in SHR and WKY. In SHR, HR increased with increasing doses of DMG (except at the near‐toxic doses of 51.15 mg kg‐1), whereas in WKY, HR decreased with increasing doses of DMG. The net change of renal SNA ranged from ‐5±3 to ‐55±12% in SHR and from ‐6±8 to ‐66±8% in WKY. Pre‐treatment withL‐arginine in SHR partly inhibited the pressor effect and attenuated the inhibition of renal SNA induced by DMG, but had little effect on HR. Thus the administration of NO inhibitor DMG could alter cardiovascular function and sympathetic nerve activity, and subsequently resulted in

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.571334000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

Role of endogenous endothelins (ET) in the control of cardiovascular system and renal function, and ET interaction with urodilatin (URO) were studied in anaesthetized rats. Activity of ET was blocked using PD 145065 (5 mg kg‐1body wt i.v.), a non‐selective antagonist of ETAand ETBreceptors. PD 145065 decreased mean arterial blood pressure (MBP) from 114±4 to 109±4 mmHg and the renal blood flow (RBF) from 6.6±0.3 to 5.8±0.4 mL min‐1(P<0.02) and increased renal vascular resistance (RVR) from 17.7±1.2 to 20.1±2.1 mmHg min mL‐1. Heart rate (HR) and renal function were not affected. URO was infused i.v. at 0.1 nmol min‐1  kg‐1body wt without or with previous ET receptor blockade. After pre‐treatment with PD 145065, infusion of URO decreased MBP more than did URO alone: 15±3% vs. 7±2% (P<0.05). RVR and HR did not change after URO alone but decreased with URO given to PD 145065 treated rats (19±5% and 14±3%, respectively,P<0.01). It is concluded that in anaesthetized surgically prepared rats endogenous ET can cause renal vasodilation, in contrast to constriction of systemic vasculature. Enhancement by ET blockade of vascular systemic and renal effects of URO supports ET interaction with natriuretic peptides in the control of cardiovas

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.583331000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

A novel application of laser Doppler flowmetry (LDF), laser Doppler perfusion imaging (LDPI), was used to study cerebral cortical blood flow (CBFcortex). In contrast to the conventional laser Doppler perfusion monitor, LDPI creates two‐dimensional maps of the tissue perfusion in a well defined area of up to 120×120 mm comprising 4096 measurement points. Measurements of CBFcortexwere made through an optically transparent polyester film applied to a cranial window preparation in ventilated anaesthetized pigs. Temporal and spatial heterogeneity in CBFcortexwere visualized by LDPI during provocations which are known to alter CBF (varying arterialPCO2or MABP, or infusion of adenosine at constant MABP (concomitant angiotensin administration) or by hyperoxemia). During hypercapnia the recorded CBFcortexincreased homogeneously. The adenosine‐mediated increase in recorded CBFcortexwas concentrated on the lower flow interval, as was the hyperoxemia‐caused decline. At decreasing MABP the autoregulatory threshold was found to vary locally within the cortex. The results suggest that LDPI, apart from detecting localized changes in CBFcortex, also visualizes flow changes within different vascular segments. Together with the practical advantages of the system, i.e. not necessitating direct contact with the tissues, this feature makes the technique suitable for studies of CBFcortexdistrib

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.560333000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

Adenine nucleotides, lactate and pyruvate were monitored by microdialysis in pig hearts, comprising four experimental groups. Two preconditioned groups, one β‐blocked by metoprolol (0.3 mg kg‐1body wt;n=6) and the other (n=7) without β‐blockade. Two groups were not preconditioned, one β‐blocked (n=6) and one without β‐blockade (n=7). Probes were inserted into ischaemic and non‐ischaemic myocardium. Preconditioning consisted of four consecutive 10 min periods of ischaemia each separated by 20 min of reperfusion. All animals were subjected to 40 min of index ischaemia followed by 25 min of reperfusion. Myocardial cAMP content was determined in biopsies after the final reperfusion and was found low in the β‐blocked groups. Lactate levels during index ischaemia exceeded the basal level 4–6‐fold in dialysate. Adenosine concentration reached 12 μmolL‐1during the first preconditioning period while an attenuation was typical for the following three preconditioning periods. The sum of the concentrations of adenosine, inosine and hypoxanthine was significantly lower during index ischaemia in the preconditioned groups displaying a peak value of 115 μmolL‐1. The corresponding value for unpreconditioned hearts was 230 μmolL‐1. The part of adenosine was 5% and less than 1%, respectively. Pyruvate concentration decreased during each brief ischaemic period of preconditioning rising to a higher level of reperfusion. The decrease in pyruvate was smaller in the controls during index ischaemia. The effects of β‐blockade and preconditioning on ischaemic metabolism were comparable and the results of the two treatments

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.558336000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

The aim of study was to assess acute effects of the divalent manganese ion (Mn2+) in an intact but isolated heart preparation. Rat hearts were perfused in the Langendorff mode at constant flow rate. Left ventricular (LV) developed pressure (LVDP), LV pressure first derivatives (LVdp/dtmax and min), heart rate (HR) and aortic pressure (AoP) were recorded. Ventricular contents of high energy phosphate compounds (HEP) and Mn metal were measured at the end of experiment. Infusion of MnCl2for 5 min with perfusate concentrations 1–3000 μMinduced an immediate depression of contractile function at and above 30 μMand negative chronotropy at and above 300 μM. These EC50values were found (μM): LVDP 250; LVdp/dtmax 160; LVdp/dpmin 120; HR 1000; and increase in AoP 80. Recovery of function during a 14 min washout period was rapid and extensive, except for Mn2+3000 μM. Somewhat unexpected, Mn2+30–1000 μMraised coronary vascular resistance up to about twice the control level, whereas the vasoconstrictory response was overcome at 3000 μM. Mn2+3000 μMreduced tissue HEP. Ventricular Mn content rose stepwise for perfusate Mn2+above 1 μMup to about 55 times the control level for perfusate Mn2+3000 μM. It is concluded that: acute effects of Mn2+like depression of contractility and rate is rapidly reversible; and rat hearts accumulate and buffer large amounts of Mn2+without affecting cardiac function or energy metabolism in th

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.d01-841.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

On two occasions, seven male endurance‐trained cyclists performed exhaustive exercise on a cycle ergometer in the morning after they had performed a bout of exercise the preceding evening in an attempt to lower the muscle glycogen stores. The subjects exercised at a work rate corresponding to ≈70% of their maximal oxygen uptake for 60 min, followed by another 20 min of maximal exercise. During exercise the subjects were given either a solution of branched‐chain amino acids (BCAAs) or flavoured water (placebo). Every 10 min during exercise the subjects rated their perceived exertion and mental fatigue on two different Borg scales. During the 60 min exercise at a given work rate, the subjects' ratings of perceived exertion when they were given BCAAs were 7% lower, and their ratings of mental fatigue were 15% lower, than when they were given placebo. In addition, the performance in the colour task of Stroops' Colour Word Test performed after exercise was improved when BCAAs had been ingested during exercise, compared with the results from the placebo trial. There was no difference in the physical performance between the two trials, measured as the amount of work done during the last 20 min of exercise when the subjects performed at their maximum. The plasma concentration ratio of free tryptophan/BCAAs, which increased by 45% during exercise and by 150% 5 min after exercise in the placebo trial, remained unchanged or even decreased when BCAAs were ing

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.547327000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

A continuous production of nitric oxide (NO) takes place in human nasal airways. NO in the nasal airways is mainly derived from the paranasal sinuses. The factors that regulate NO synthesis in the upper airways are presently not known. We have investigated the effects of physical exercise on NO levels in the nasal airways. Nasal cavity NO levels were measured by chemiluminescence technique in five healthy non‐smoking male subjects before, during and after 5 min of maximal exercise (245 W) on an ergometer cycle. In addition, in one subject NO levels were measured directly in the maxillary sinus during exercise. Nasal cavity NO levels were decreased by 47% after only 1 min of exercise compared with the control situation. A maximal 76% reduction was found at the end of the exercise period and thereafter NO levels slowly increased, reaching basal levels again in about 15–20 min. NO levels in the sinus decreased in a similar manner during exercise. The decrease in nasal cavity NO levels cannot be explained merely by dilution of nasal air due to changes in nasal cavity volume or increased ventilation. We conclude that the excretion of NO in the nasal airways is decreased acutely during heavy short term physical exerc

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.68339000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

Positive end‐exspiratory pressure (PEEP) and nitric oxide (NO) can influence lung VA/Q‐matching and pulmonary vascular resistance, and application of PEEP can increase exhaled NO in animals. To obtain a better understanding of these mechanisms, we examined how different types of ventilation or changes in CO2affect the formation of endogenous NO. Exhaled NO in pentobarbital‐anaesthetized rabbits was monitored by chemiluminescence. The animals were enclosed in a chamber and subjected to various modes of positive as well as negative pressure ventilation which was adjusted to induce similar changes in functional residual capacity (FRC) with maintained ventilatory rate and tidal volume. In addition, stepwise increase in FiCO2(1.0–10%) was studied. Negative extrathoracic end‐exspiratory pressure during negative extrathoracic pressure ventilation produced an increase in NO production similar to that of positive end‐exspiratory pressure during positive pressure ventilation, the increase consisting of an initial peak followed by a plateau. The faster the FRC was increased, the higher was the initial peak in NO. The greater the increase in FRC, the higher was the plateau NO concentration. Increased FiCO2caused a dose‐dependent reduction in exhaled NO. The observations of lung distension effects on exhaled NO suggest the possibility of stretch‐receptors or ‐receptive mechanisms coupled to NO formation within the lung. In addition, NO formation in the lung is influenced by CO2in a r

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.568335000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

In the present study we have characterized receptor‐mediated Ca2+signalling patterns as well as Ca2+‐mediated ion transport mechanisms in collagenase isolated rat pancreatic acini. Measurements of the initial Ca2+response to maximal carbachol stimulation revealed a rapid increase in [Ca2+]i, which, in general, occurred synchronously throughout the cells. Less frequently, not all cells in the acinus responded to carbachol, but did respond to subsequent stimulation with bombesin, indicating that not all cells possess receptors for all the applied agonists. In view of the heterogeneity in the agonist‐evoked Ca2+responses, ionomycin was used to assess the role of Ca2+in activating K+, Na+and Cl‐transport mechanisms. Ionomycin induced a rise in [Ca2+]i, thereby increasing Cl‐permeability as well as stimulating K+efflux, probably through non‐specific cation channels. However, the resting K+efflux was insensitive to blockers of non‐specific cation channels, indicating the existence of a selective resting K+conductance. Ionomycin also stimulated influx of Na+, which in part was mediated by non‐specific cation channels. The changes in ion fluxes measured in the present study revealed that when [Ca2+]iis raised in rat pancreatic acini, they gain Na+and Cl‐and lose K+, with non‐specific cation channels being essenti

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.545329000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY

摘要:

The effects of 4 weeks of thyroid hormone (3,5,3′‐triiodothyronine, T3) treatment on the expression of myosin heavy chain (MyHC) isoforms were examined in young (3–6 months) and old (20–24 months) female rats, and compared with those in age‐matched male rats (Larssonet al.1995). In control rats, ageing was associated with a type IIA to I MyHC isoform switching in the slow‐twitch soleus and a type IIB to IIX MyHC isoform switching in the fast‐twitch extensor digitorum longus muscle (EDL). Gender‐ and muscle‐specific differences were observed in the regulation of MyHC isoforms by T3. In the soleus, dramatic downregulation of the type I and upregulation of the type IIA MyHC isoform were observed in both females and males, but upregulation of the IIX MyHC isoform was observed only in male rats. In EDL, T3 treatment had no significant influence on the MyHC isoform composition in the males irrespective of the age of the animal. In the females, on the other hand, T3 treatment resulted in a significant MyHC transformation from IIA to IIB, probably via IIX myosin, in spite of the fact that type IIA mRNA has been reported to be downregulated in both females and males. It is concluded that the regulation of MyHC isoforms by thyroid hormone differs between females and males, presumably as a result of a gender‐related difference in the translational or post‐translational regulat

ISSN:0001-6772    

DOI:10.1046/j.1365-201X.1997.559328000.x

出版商:Blackwell Science    

年代:1997

数据来源: WILEY