摘要:

Eight healthy men performed supine one‐legged training on a bicycle ergometer 45 min per leg four times per week for 4 week. The ergometer and lower body were inside a pressure chamber, the opening of which was sealed at the level of the crotch. One leg trained with impeded leg blood flow (I‐leg), induced by an increased (50 mmHg) chamber pressure, at the highest tolerable intensity. The contralateral leg trained at the same power under normal pressure (N‐leg). Before and after training biopsies were taken from the vastus lateralis of both legs and maximal one‐legged exercise tests were executed with both legs. Biopsies were repeated when the subjects had been back to their habitual physical activity for 3 months. Training increased exercise time to exhaustion, but more in the I‐leg than in the N‐leg. After training, the I‐leg had higher activity of citrate synthase (CS), a marker of oxidative capacity, and lower activity of the M‐subunit of lactate dehydrogenase isoenzymes. It also had a higher percentage of type‐I fibres and a lower percentage of IIB fibres, larger areas of all fibre types and a greater number of capillaries per fibre. It is concluded that ischaemic training changes the muscle metabolic profile in a direction facilitating aerobic metabolism. An altered fibre‐type composition may contribute, but is not enough prerequi

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09554.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The force‐velocity relation has been studied during calcium‐induced contracture of chemically skinned fibres from the semitendinosus muscle ofRana temporariawith special interest focused on the high‐load region. The force‐velocity curve was hyperbolic at low and intermediate loads but departed below the hyperbola as the load exceeded about 80% of the isometric force (Po). The force intercept (P*o) of the hyperbola derived from force‐velocity data truncated at 0.78Powas higher thanPo(P*o/Po= 1.14±0.04). At submaximum Ca2+concentration, where the isometric force of the fibre was 65–75% of the maximum value, the force‐velocity data still departed below the hyperbola at high loads (Po/Po= 1.09±0.04). The departure of the force‐velocity data from the hyperbola at high force was also found at high ionic strength (250 mM), but not at low ionic strength (150 mM) (Po/Po= 1.09±0.03 and 0.98±0.03, respectively). The force‐velocity relations derived under different experimental conditions could be fitted well by a modified version of Hill's (1938) hyperbolic equation (Edman 1988) using similar numerical values ofk1andk2in the latter equation. The results indicate that the force‐velocity relation in skinned muscle fibres is biphasic, and that the two curvatures, as in intact muscle fibres, are closely related to one another. Furthermore the evidence supports the hypothesis that the altered shape of the force‐velocity relation at high loads is not related to the force level per se but rather to the speed of shortening of the contra

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09555.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Lowering myocardial temperature increases contractile force, presumably by increasing intracellular calcium content. To study the mechanisms behind this, we compared the effects of some known inotropic interventions with hypothermia on mechanical restitution and post‐rest contractile force in isolated guinea‐pig papillary muscles. In four groups (n= 6 per group), the effects of: (1) reducing the ability for Na/Ca exchange to extrude Ca2+(a) by increasing [Na+]1with ouabain or (b) by increasing [Ca2+]o; and (2) activation of calcium channels with Bay‐K 8644, were compared with lowering temperature from 37 to 27 °C. Normally (at 37 °C and 2 mm CaCl2), mechanical restitution could be described by a rapid recovery phase with a time constant between 180 and 220 ms, followed by a slowly decaying phase with a time constant between 5000 and 8000 ms and post‐rest contractions (1–10 min rest) were markedly depressed compared to steady‐state contractions. Steady‐state developed force was markedly increased at 27 °C, after 1 μm ouabain, 6 mm CaCl2or 0.1 μM Bay‐K 8644. At 27 °C the rapid recovery phase of restitution was delayed while the slowly decaying phase was not affected. Ouabain and increased [Ca2+]ocaused elevation of the slowly decaying phase of restitution and markedly attenuated the post‐rest depression of developed force, which may be attributed to a reduced diastolic extrusion of Ca2+via the Na/Ca exchanger. Hypothermia and Bay‐K 8644 on the other hand, augmented this post‐rest depression. Hence, this study suggests that increased Ca2+influx due to delayed inactivation of calcium channels may account for the increased developed force during hypothermia rather than reduced diastolic extrusion of

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09556.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Contractions in the rat portal vein, evoked by spontaneous action potentials or depolarizing high‐K+solution, are rapidly and reversibly inhibited by hypoxia or respiratory blockade. Intracellular free calcium ([Ca2+]i) was measured using Fura‐2 to evaluate the effects of metabolic blockade on excitation–contraction coupling. Spontaneous contractions were associated with transient increases in [Ca2+]i. During exposure to cyanide (0.2–0.4 mm) or 2,4‐dinitrophenol (30μm) the duration and amplitude of the Ca2+transients were decreased, leading to a decreased mean time integral of the individual [Ca2+]itransient, and corresponding decrease in the duration and amplitude of the contraction. Basal [Ca2+]iwas increased in the presence of the metabolic inhibitors. High‐K+(40 mM) contractions caused a sustained increase in [Ca2+]i, which was not inhibited by exposure to cyanide, although the amplitude of the associated contraction was greatly reduced. Together with the earlier demonstration of decreased 20 kD myosin light chain phosphorylation under these conditions, this indicates that the activation of contraction is influenced by metabolism via the energy dependence of the light chain phosphorylation reaction. Thus at least three steps in the excitation–contraction sequence are influenced by inhibition of oxidative metabolism: membrane excitation, light chain phosphorylation, and the cross‐bridge cycle. This provides mechanisms for a high degree of metabolic sensitivity of vascular tone, of importance for the adaptation of blood flow to tissue m

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09557.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Results fromin vitrostudies have indicated that endothelin‐1 is a main candidate for endothelium‐derived contracting factors. The aim of thisin vivostudy was to describe in quantitative terms the effects of endothelin‐1 (ET‐1), and of ETareceptor blockade, on vascular tone (resistance) in large‐bore arterial resistance vessels (>25 μm), small arterioles (<25 μm) and the veins, as well as on capillary pressure and fluid exchange in cat gastrocnemius muscle. Endothelin‐1 (100–1600 ng kg‐1 min‐1, i.a.) elicited, after an initial transient dilation, a strong dose‐dependent constrictor response in all three consecutive vascular sections, yet with a preferential action on the small arterioles and the veins. The vasoconstriction developed very slowly over about 1 h and was also long‐lasting after cessation of the infusion. Our main quantitative analysis refers to effects elicited by 20 min long i.a. infusions of ET‐1 at a dose of 400 ng kg‐1 min‐1. At the end of this period, the peptide caused, on average, a three‐fold increase in total regional vascular resistance, in turn explained by a 70% increase in large‐bore arterial resistance, a 280% increase in arteriolar resistance and a 220% increase in venous resistance. The latter effect was also manifested as a pronounced capacitance response, and as a decrease in the pre‐ to post‐capillary resistance ratio leading regularly to a rise in capillary pressure, net transcapillary fluid filtration and oedema formation which is unusual for a vasoconstrictor. The new specific competitive ETAreceptor antagonist FR 139317 was found to be fully effectivein vivo, insofar as it abolished the constrictor response to endothelin‐1. ETAreceptor blockade, or administration of phosphoramidon, an inhibitor of ET‐1 production, did not influence the level of basal vascular tone, indicating no significant endogenous release of ET‐1 under resting conditions. This contrasts to the established pronounced endogenous release of endothelium‐derived nitric oxide. Finally, vascular myogenic regulation was found not to be mediated by ET‐1. The results, taken together, suggest a possible role of ET‐1 in long‐term, rather than short‐term, regulation of vascular tonein vivo, pe

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09558.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The aim of this study was to clear up whether the flow‐induced dilation of arteries is sufficient to ensure invariability of pressure drop along these vessels under many‐fold increase in blood flow rate. In anaesthetized rats an arteriovenous shunt was constructed by connecting the saphenous artery and the femoral vein. Resistance of the shunt was changed by a device creating either rectangular flow pulses of different amplitude or slow linear ramps of flow rate. Pressure drop along the arterial cascade, from the aortic arch up to distal saphenous artery, was recorded and the steady‐state flow‐pressure drop relationship was determined. At low flow rates (<0.25–0.3 ml min‐1) the pressure drop rose proportionally to flow, i.e. as in a system of ordinary tubes with non‐regulated diameter. In contrast, at higher flow rates (up to 1.5 ml min‐1) the pressure drop either remained unchanged under 3‐ to 5‐fold increases of flow rate or rose far less than the flow. Thus, the pressure drop stabilization effect has been evidenced. The threshold of this effect was about 0.3 ml min‐1, corresponding to the ‘resting’ flow in the saphenous artery, i.e. the narrowest of all the cascade vessels. This coincidence suggests that the pressure drop stabilization is determined by the flow‐induced dil

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09559.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

To ascertain whether the relative invariance of the pressure drop along the arterial cascade—from the aortic arch down to include the saphenous artery—during increases of saphenous outflow (Khayutinet al. 1993), is determined mainly by dilation of the latter, and to discover whether this invariability is a manifestation of endothelium‐mediated vasodilation, the pressure drop along the rat saphenous artery was measuredin situduring exposure of the artery to rectangular pulses or slow ramps of blood flow. At flow rates below a critical value of about 0.3 ml min‐1, flow increase was followed by a proportional increase of pressure drop. In contrast, with further flow increase, up to the values five to six times beyond the critical one, the steady state pressure drop did not increase at all, or only to a minor extent. This ‘pressure drop stabilization’ was shown to be unrelated to the decline of distending pressure, but to result from a true artery dilation commensurate with the flow increase. Interference with the endothelium by way of 90 mm hydrogen peroxide eliminated the stabilization effect, whereas noradrenaline‐induced constrictions could be increased about three‐fold. The ‘threshold’ shear stress on the endothelium, needed to initiate saphenous artery dilation, was estimated to be 74±4 dyn cm‐2. The functional importance of stabilizing the pressure drop along the arterial conductance and resistanc

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09560.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

To examine the hypothesis that hypoxic pulmonary vasoconstriction may have a slower time course and greater intensity than is currently recognized, experiments were conducted in twelve anaesthetized rabbits subjected to unilateral lung hypoxia for 6 h. Endobronchial cannulation was used to maintain apnoea of one lung at constant airway pressure whilst inflating the lung with nitrogen or liquid. The second lung was ventilated with oxygen to maintain normocapnia and oxygen transfer. A pulmonary artery catheter was introduced non‐invasively. Pulmonary shunt was derived from mixed venous and arterial blood gas parameters. Pulmonary artery pressure was monitored continuously and cardiac output was estimated from oxygen uptake measurements before and after 6 h unilateral hypoxia. The experiments show that a rapid phase of hypoxic pulmonary vasoconstriction is followed by a slow phase which develops over hours. The slow phase is associated with a massive blood flow diversion from the hypoxic lung, such that pulmonary shunt after 6 h unilateral hypoxia is indistinguishable from baseline shunt during bilateral ventilation with oxygen. The response is reversible, but with a similarly slow time course. Results from nitrogen and liquid filling of the lung are similar. These findings are consistent with early experiments by Dirken and Heemstra in 1948 (Quart J Exp Physiol34, 193–211), and challenge the prevailing notion that hypoxic pulmonary vasoconstriction is always a rapid and relatively weak physiological response to hypo

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09561.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The rostral ventrolateral medulla (rVLM) is known to play an important role in cardiorespiratory control. In the rVLM an ‘apnoea region’, in which unilateral focal blocks induce strong depressant effects on inspiratory activity up to complete apnoea, has been described. This study was designed to systematically investigate the effects provoked by unilateral micro‐injections (10–30 nl) ofd,l‐homocysteic acid 160 mm into this region on respiratory activity and arterial blood pressure in pentobarbitone anaesthetized, vagotomized, paralyzed and artificially ventilated cats. Micro‐injections into the rostral portion of this area caused depressant respiratory responses up to complete apnoea, while micro‐injections into more caudally located sites induced excitatory respiratory responses. Similar effects were observed in the activity of phrenic nerves and inspiration‐related medullary neurons of both the dorsal and ventral respiratory group. The respiratory responses could be accompanied by marked increases in blood pressure (≥30 mmHg), especially at locations ventral to the retrofacial and facial nucleus; however, they could also occur in the absence of appreciable changes or even in association with slight decreases in blood pressure. Similar respiratory and pressor effects were observed in carotid sinus denervated cats. The results indicate that two distinct rVLM neuronal populations, one located more rostrally and the other more caudally, may have an important role in the genesis and/or maintenance of respiratory rhythm by exerting respectively inhibitory and excitatory influences on inspiratory activity. Furthermore, they support the hypothesis that different neural substrates of the rVLM are involved in the regulation of respiratory and cardiov

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09562.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The possible role of humoral factors in the control of shivering in the common eider duck (Somateria mollissima) was investigated using a cross‐circulation technique. Pairs of animals were coupled so that the arterial system of one animal was connected to the venous system of the other. The rate of blood transferral was 12.8 ml min‐1. By adequate heparinization of the extracorporeal blood supply, cross‐circulation could be maintained for periods of up to 12 h. The temperature of blood entering each animal (Tinlet) was controlled by heat exchangers. During control experimentsTinletwas maintained at a temperature close to normal body temperature. During cooling experimentsTinletwas maintained atc. 20 °C. Changes in metabolic heat production and oesophageal temperature in response to blood cooling were measured in cross‐circulated pairs of animals cooled simultaneously or individually. Based on analysis of the metabolic responses under the different experimental situations, no evidence was found to indicate that blood‐borne substances are involved in the shivering response in the

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1993.tb09563.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY