摘要:

To examine the respective roles of malnutrition and phosphate depletion on muscle exercise capacity and bioenergetics, phosphate‐depleted, either underfed or partly refed rats; phosphate‐supplemented, either underfed or partly refed rats; and well‐nourished control animals were studied, using swim time to exhaustion and31P NMR spectroscopy measurements of muscle phosphocreatine, inorganic phosphate, adenosine triphosphate and intracellular pH. Only partly refed rats displayed hypophosphataemia. Swim time to exhaustion was lower in non‐refed rats than in controls. Among the four groups, both refeeding and phosphate depletion positively affected swim time to exhaustion (both withP<0.02), and swim time to exhaustion was negatively correlated with phosphataemia (P<0.05). At rest, the ratio of muscle phosphocreatine/inorganic phosphate was lower in the phosphate‐supplemented rats than in controls, whereas muscle phosphocreatine/adenosine triphosphate and intracellular pH were comparable. After non‐tetanic stimulation, the muscle phosphocreatine recovery was slower in the four groups than in controls and closely correlated with exhaustion (P<0.01). These findings suggest that malnutrition alters the capacity of muscular work, mainly because of a reduced cell oxidative energy availability. These patterns are improved by partial refeeding and clearly influenced by the level of phosphorus intake, whether depletion is capable of improving metabolic alterations or uncontrolled supplementation is deleterious in malnouris

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09260.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Controversy exists whether recruitment of a large muscle mass in dynamic exercise may outstrip the pumping capacity of the heart and require neurogenic vasoconstriction in exercising muscle to prevent a fall in arterial blood pressure. To elucidate this question, seven healthy young men cycled for 70 minutes at a work load of 5540%VO2max. At 30 to 50 minutes, arm cranking was added and total work load increased to (mean ± SE) 82 ± 4% ofVo2max. During leg exercise, leg blood flow average 6.15 4.511 minutes‐1, mean arterial blood pressure 137 ± 4 mmHg and leg conductance 42.3 ± 2.2 ml minutes‐1mmHg‐1. When arm cranking was added to leg cycling, leg blood flow did not change significantly, mean arterial blood pressure increased transiently to 147 ± 5 mmHg and leg vascular conductance decreased transiently to 33.5 ± 3.1 ml minutes‐1mmHg‐1. Furthermore, arm cranking doubled leg noradrenaline spillover. When arm cranking was discontinued and leg cycling continued, leg blood flow was unchanged but mean arterial blood pressure decreased to values significantly below those measured in the first leg exercise period. Furthermore, leg vascular conductance increased transiently, and noradrenaline spillover decreased towards values measured during the first leg exercise period. It is concluded that addition of arm cranking to leg cycling increases leg noradrenaline spillover and decreases leg vascular conductance but leg blood flow remains unchanged because of a simultaneous increase in mean arterial blood pressure. The decrease in leg vascular conductance observed when arm cranking increased mean arterial blood pressure could be regarded more as a measure to prevent overperfusion than a measure to maintain arterial

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09261.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The degradation of adenosine triphosphate, phosphocreatine and glycogen was determined in type I and type II fibres of the human quadriceps femoris muscle during intermittent electrical stimulation at 20 and 50 Hz, (1.6 seconds stimulation, 1.6 seconds rest). Seven healthy volunteers took part in the study. Muscle biopsy samples were obtained at rest and after 10 and 20 seconds of stimulation (six and 12 contractions, respectively). The resting contents of adenosine triphosphate, phosphocreatine and glycogen were all higher (P<0.05) in type II fibres compared to type I fibres. By the end of stimulation, whole muscle force production had declined to 84 and 77% of the initial force at 20 and 50 Hz, respectively. The phosphocreatine degradation rate after 10 and 20 seconds of stimulation was greater in type II fibres (P<0.05) compared to type I fibres at both 20 and 50 Hz. The rates of glycogenolysis after 20 seconds stimulation in type II fibres were 3.18±1.1 and 6.31±1.39mmol glycosyl units kg‐1s‐1. The corresponding rates in type I fibres were 0.46 ± 0.73 and 0.60 ± 0.39 mmol glycosyl units kg‐1s‐1which were not significantly different from zero. It is hypothesized that the decline in whole muscle force observed during electrical stimulation may be a consequence of the rapid loss of PCr stores in typ

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09262.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Healthy males were examined before and after 12 weeks of accommodated resistance training (three week‐1) and after 12 weeks of detraining. Training consisted of four to five sets of six coupled maximum voluntary bilateral concentric and eccentric (Grp ECCON;n= 10) or 12 concentric (Grp CON;n= 8) quadriceps muscle actions. Concentric and eccentric peak torque at various constant angular velocities and three repetition maximum half‐squat and vertical jump height were measured.Grp ECCON showed greater (P<0.05) overall increase in peak torque after training and detraining than Grp CON. Thus, concentric peak torque (0.52 rad s‐1) increased more (P<0.05) over the experimental period in Grp ECCON and increases in eccentric peak torque were preserved in Grp ECCON only. Increases in peak torque in response to training were greater (P<0.05) at 0.52 than at 2.62 rad s‐1. Alterations in the torque‐velocity patterns induced by training remained after detraining in Grp ECCON but not in Grp CON. The retained increases (P<0.05) in half‐squat were 12 and 18% in Grps CON and ECCON, respectively. Neither group showed increased vertical jump height after detraining.This study showed greater preservation of concentric and eccentric peak torque after detraining following coupled concentric and eccentric than concentric resistance training. Only the former regime induced a change in the shape of torque‐velocity curves that was manifest after detraining. These results suggest that the performance of eccentric muscle actions is critical to optimize increases in muscular strength in response to heavy resistance training, because it probably induce greater and more long‐lived neural adaptations than the performance of con

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09263.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Seven subjects underwent a standard localized exercise of calf muscles in order to investigate whether the metabolic exercise‐induced steady‐state, as revealed by the evaluation of inorganic phosphate/phosphocreatine ratio, depends on the conditioning of the muscle just prior to the exercise. The experimental protocols consisted of two separate experiments using first [31P]nuclear magnetic resonance spectroscopy and second (on 3 subjects) infrared oxyphotometry to respectively follow variation of energy metabolism and tissular deoxygenation. The exercise consisted of 240 successive plantar flexions (0.5 Hz frequency) against a high load equivalent to SO% of the maximal voluntary contraction. This exercise was accomplished before cold exercise and after warm exercise, a warming‐up period bringing to approximately 50% ofVo2max. The results showed that: (1) steady‐state level of phosphate/phosphocreatine and intracellular acidosis was significantly lowered by warming‐up; (2) cold and warm exercise steady‐state of calculated adenosine diphosphate values were not significantly different; (3) cold exercise rapidly induced a high tissular deoxygenation that is not observed during warm exercise; and (4) time‐constant of phosphocreatine resynthesis is lowered after warm exercise but the initial slope of time‐evolution is not modified. Parallel experiments also showed that phosphate/phosphocreatine steady‐state was not modified in comparison with warm exercise when the same power of exercise was reached by stepwise incrementation of the charge. From these results we postulate that a better tissue oxygenation due to a global or localized warming‐up allows to reach the same mechanical performance with a lower decrease of PCr content, owing to a faster adjustment of oxidative metabolism during the transitional period. However the aerobic pathway flux during the steady‐state is probably the same before and after the warming‐up despite different values of phosphate/phosphocreatine. As a consequence it can be assumed that this ratio is not a good indicator of the rate of muscle oxidative metabolism during the steady‐st

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09264.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The relationship between myocardial lactate extraction and blood lactate concentration and the possibility that simultaneous uptake and release of lactate occur in the normal human heart was investigated by measuring arterial‐coronary sinus differences of lactate and of labelled lactate during infusion of14C lactate in 13 healthy young male volunteers. Measurements were done at rest, during increased cardiac work with unaltered arterial lactate concentration achieved by atrial pacing and during increased cardiac work and increased arterial lactate concentration achieved by supine cycle ergometer exercise. There was on no occasion a significant difference in14C lactate specific activity between arterial and coronary sinus blood, i.e. no significant admixture of non‐labelled lactate occurred in the coronary sinus indicating that on no occasion was there any sign of lactate release. The myocardial extraction of lactate seemed to be a linear function of arterial lactate concentration. During exercise with an arterial lactate concentration of 6 mmol l‐1and above, lactate could have covered approximately 75–100% of the oxidative metabolism. Thus, during short‐term heavy work myocardial lactate extraction dominates over other substrates (mainly free fatty acids and glucose) taken up by the heart, and used for oxidation by the heart mus

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09265.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

To determine the acute effect of reduced barometric pressure and hypoxia on renal nerve activity, urethane‐anaesthetized and mechanically ventilated rabbits were randomly exposed to the following four separate conditions in a decompression chamber: hypoxic hypoharia (n=71, hypoxic normobaria (n= 5), normoxic hypoharia (n= 8) and slow normoxic hypobaria (n= 7). A combination of rapid decompression and simultaneous adjustment of inspiredPO2was used to simulate an altitude of 6600 m, and renal nerve activity and haemodynamics, such as systemic blood pressure and heart rate, were measured. During both hypoxic hypobaria and hypoxic normobaria, there were significant and similar increases in renal nerve activity at 6600 m (54 ± 7% and 61 ± 13% from each baseline, respectively). However, there were no changes in renal nerve activity during normoxic hypoharia or slow normoxic hypoharia with decompression rates of 1000 or 400 m min‐l, respectively. From these results, we conclude that a reduction in barometric pressure without hypoxia does not affect renal nerve activity in anaesthetized ra

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09266.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

In human D384 astrocytoma cells, cyclic AMP accumulation can be conveniently studied after labelling of the adenosine triphosphate pool (15 fmol cell‐1) with [3H]adenine. In this study, adenosine had a biphasic effect on cyclic AMP accumulation, which was scarcely altered by blocking adenosine uptake and metabolism. Low concentrations of adenosine led to an inhibition of cyclic AMP accumulation, and higher concentrations led to stimulation. No effect of adenosine on cyclic AMP was observed unless phosphodiesterase was inhibited by rolipram.The A1receptor antagonist DPCPX attenuated the inhibitory phase of adenosine response, and enhanced the cyclic AMP accumulation induced by adenosine analogues. The cyclic AMP accumulation was stimulated by NECA>ADO>CGS 21680>CV 1808>CPA ≥ CHA, indicating mediation by A, receptors. The stimulatory effect of NECA was much more effectively blocked by the combined A1and A2receptor antagonist CGS 15943 (KB4 nmol I‐1) than by theA1antagonist DPCPX (KB110 nmol 1‐l). Treatment of the cells with pertussis toxin (0.2 μgml‐1for 2.5 h) potentiated the cyclic AMP response to adenosine analogues significantly. The cyclic AMP response to NECA was enhanced by the protein kinase C activator phorbol dibutyrate even after pertussis toxin treatment. By contrast, nanomolar concentrations of bradykinin, which increases Ca2+‐levels and protein kinase C activity in D384 cells, reduced NECA‐induced cyclic AMP accumulation in control and pertussis toxin‐treated cells.Thus, D384 cells possess both A1and A2adenosine receptors influencing cyclic AMP in opposite directions. A2receptor‐mediated cyclic AMP accumulation can be stimulated by activating protein kinase C and inhibited by raising Ca2+. Neither the effects of protein kinase C activation nor those of bradykinin required pertussis toxin‐

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09267.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The aim of the present investigation was to modify the widely used isolated perfused rat kidney preparation to make it more suitable for studies of glomerular permeability to macromolecules. Both kidneys were perfusedin situusing separate pumps in two of each other independent systems with Tyrode‐solution containing human serum albumin (18.2 g 1‐1). Sodium nitroprusside was administered to induce dilatation and to maintain constant vascular resistance (PRU100) during the experiments. The addition of sodium nitroprusside decreased vascular resistance from 0.17 ± 0.05 to 0.09 ± 0.02 mmHg min‐l100 g‐1ml‐1and increased urine flow and glomerular filtration rate. The temperature of the perfusate was reduced from 37°C to 8°C to inhibit tubular reabsorption of protein and fluid, resulting in a urine to plasma concentration ratio of [51Cr]EDTA of 1.26 ± 0.07. Furosemide reduced the urine to plasma concentration ratio for [51Cr]EDTA further to 1.15 ± 0.02 and increased glomerular filtration rate. Moreover, by performing the studies at low temperatures (8°C) in the presence of sodium nitroprusside and furosemide it was possible to achieve low and stable albumin fractional clearance values close to those prevailingin vivo. Thus, the described technique, allowing simultaneous perfusions of both kidneys with different solutions, pressures and flows, seem to be well suited for studies of macromolecular transport across glomer

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09268.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Centrally administered thyrotropin‐releasing hormone exerts a well documented hypertensive effect. In this study, the possible physiological role of thyrotropin‐releasing hormone in the central cardiovascular regulation was evaluated in spontaneously hypertensive rats receiving long‐term (8–14 days) intracerebroventricular infusion of a heterologous antiserum to thyrotropin‐releasing hormone. The effect of this passive immunization on the blood pressure was monitored from conscious animals by the tail‐cuff method. Thyrotropin‐releasing hormone antiserum significantly decreased the systolic arterial pressure in adult rats with established hypertension. No alterations in serum thyroid hormone status were observed indicating that the antihypertensive effect of immunological blockade of thyrotropin‐releasing hormone was not due to changes in the serum thyroid hormone levels. These results provide evidence for a role of endogenous brain thyrotropin‐releasing hormone in the maintenance of hypertension in spontaneously

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1992.tb09269.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY