摘要:

The mechanical efficiency of positive work was studied in six subjects performing three different types of exercises. On the first occasion the subjects ran on a motor‐driven treadmill at 3.33 m s‐1;the second and the third exercises consisted of performing rhythmical vertical jumps for 1 min both in rebound (RJ) and no‐rebound (NRJ) conditions. The mechanical efficiency calculated in NRJ, which reflects only the conversion of biochemical energy into mechanical work, was found to be lower than the corresponding observation in RJ, 17.2vs. 27.8% (P<0.001), respectively. These differences could not be explained by only the storage and recoil of elastic energy occurring in RJ compared with NRJ. The calculated extra work delivered ‘free’ was greater than the potential elastic energy which could be stored within the leg extensor muscles (187vs. 124 J for each jump,P<0.05). It is likely that other factors might be responsible for the extra work found in NRJ. It was suggested that the difference in the length of time to perform positive work between a simple shortening contraction and a stretch‐shortening muscular activity could be also responsible for the enhanced efficiency observed in RJ. This suggestion was supported by the high relationship (P<0.001) found between the time to perform positive work and the mechanical efficiency measured in jumping and estimated dur

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08246.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Internal and external mechanical work, energy consumption and mechanical efficiency were studied in constant‐load ergometer bicycling at five different power outputs below, equal to, and above the aerobic (AerT) and anaerobic (AnT) thresholds. The gross, net and true efficiencies of the whole body in five male subjects were calculated. The work against the external load was defined as the external mechanical work. The internal mechanical work was calculated as the sum of the increments of kinetic and potential energy in all body segments by using methods of film analysis. Total energy consumption was measured by combining aerobic and anaerobic energy production. When the power output of the bicycle ergometer was increased from 146+15 to 283 ± 17 W, oxygen consumption increased from 2.20 ± 0.98 to 4.22 ± 0.201 min‐1(P<0.001), while the oxygen consumption at rest was 0.30 ± 0.03 l min‐1. The concentration of blood lactate increased from 2.2 ± 0.4 at the lowest work load to 8.6 ± 1.2 mmol 1‐1at the highest work load (P<0.001). The amount of external work done per revolution increased from 139 ± 20 to 277 ± 29 J (P<0.001), while the amount of internal work per revolution remained almost constant (56 ± 12 J). The gross efficiency in the present study was 17–20%, net efficiency 18–22% and true efficiency 21–30%, respectively. The highest gross and net efficiencies were reached at the AerT. The lowest efficiencies were obtained at highest work load. Oxygen uptake and total energy consumption were significantly higher and true efficiency lower at the

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08247.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The effects of reduced muscle perfusion pressure on dynamic exercise performance and cardiovascular and respiratory functions were investigated. Eight subjects were studied during supine cycle ergometry at stepwise increasing workloads until exhaustion with and without the legs exposed to a supra‐atmospheric pressure of 50 mmHg (Leg Positive Pressure, LPP), a novel and convenient means of reducing the perfusion pressure in the working muscles. In the LPP condition exercise performance was reduced by 40% which, judging from assessments of perceived exertion, was due to premature muscle fatigue, indicating local or overall underperfusion of the working muscles. At any given work load, the arterial pressure response was considerably stronger during LPP than in the control condition. LPP also caused greater increases in blood lactate concentration and pulmonary ventilation, the differences from control increasing with the work load. Furthermore, the ventilatory equivalent for O2at a given work load was markedly higher in the LPP than in the control condition, while exercise‐induced decreases in end‐tidalPCO2were considerably exaggerated by LPP. The augmented pressor response during flow‐restricted exercise, together with the strong ventilatory response which was out of proportion to overall O2uptake, suggests increased activation of muscle chemoreflexes by accumulation of metabolic end products, the increased pressor response tending to reduce the local flow error in the working

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08248.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The qualitative characteristics of the inotropic response to increase in extracellular calcium (Ca0) were studied in isolated, electrically driven, isometrically contracting rat papillary muscles. All experiments were done in the presence of adrenergic receptor blockers. Ca0was increased in a cumulative way by exchanging a small fraction of the incubation solution with a corresponding solution with higher calcium concentration (8 mmol 1–1). At any Ca0level there was an almost proportional increase in parameters describing different parts of the contraction‐relaxation cycle as compared with results at the preceding lower Ca0level. Time to peak tension was prolonged at high compared with low Ca0levels. The response to increased Ca0was very similar to the cyclic AMP (cAMP)‐independent inotropic response elicited through activation ofα‐adrenergic receptors (α‐type response, Skomedalet al. 1982) and strikingly different from the cAMP‐dependent inotropic response elicited, for example, through activation ofβ‐adrenergic receptors (β‐type response, Skomedalet al. 1982). As the inotropic response to increased Ca0is known to be cAMP‐independent (Döngeset al. 1977), the present results demonstrate the interrelationship between the regulatory function(s) and the direct effector function(s) of cal

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08249.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Thermogenesis in human skeletal muscle was monitored by measurement of heat production using perfusion microcalorimetry. Heat production significantly correlated with relative body weight. The energy expenditure of the Na–K‐pump (ΔP), assessed after inhibition by ouabain in Krebs‐Ringer phosphate buffer containing glucose and insulin, amounted to 6% of the total heat production in vastus lateralis muscle. Muscle potassium positively correlated with ΔP (r= 0.84,P<0.005). For rectus abdominis muscle ΔP was 8–15%; 95% confidence interval for the difference was 3–5% when comparison was made with vastus lateralis. The finding of a positive relationship between ΔP and muscle magnesium (r= 0.68,P<0.04) is possibly explained by the dependence of ATP hydrolysis on internal magnesium. Our data on resting thermogenesis in small muscle samples agree to previous estimates of O2consumption in human skeletal

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08250.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Mechanical characteristics and electrical activity were studied in the extraocular muscles of the catfish,Ictalurus punctatus. The contractile properties were determined by stimulation of the individual muscle nerve branches to lateral and medial rectii and the superior and inferior oblique muscles. The speed of contraction was higher than in most other fish muscle, with a twitch contraction time of about 12 ms and a tetanus fusion frequency of 150–170 Hz in all four eye muscles. The fatigue resistance was also high. These properties were the same in fully innervated and partially innervated muscle, largely irrespective of what part of the muscle that was activated. Although different fibre types are known to exist in fish extraocular muscle, it was not possible to obtain functional separation of the mechanical force profile even in the lateral rectus with two distinct motoneuronal innervations. We suggest that polyneuronal innervation of the muscle fibres produces the mechanical responses. Since EMG activity during spontaneous eye movements was similar in the global and the orbital parts of the muscle, all types of fibres in fish extraocular muscle are probably recruited for all types of eye movement

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08251.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

In the rat eye, intracameral injections of substance P in doses of 10–30 pmol caused a maximal long‐lasting miosis and a leakage of plasma proteins into the aqueous humor, indicating a breakdown of the blood‐aqueous barrier. Neurokinin A seemed equipotent to SP, but calcitonin‐gene‐related peptide (CGRP) (17 pmol) caused neither moisis nor protein leakage into the aqueous humor. The same result was obtained when CGRP was administered intravenously. Intracameral injection of capsaicin caused only a transient moisis which could not be repeated with further injections, even though the pupillary sphincter was still able to react to exogenous SP.Antidromic electrical stimulation of the trigeminal nerve caused plasma extravasation in the skin and a breakdown of the blood‐aqueous barrier with an increased protein content in the aqueous humor. The stimulation did not affect the pupil size. The results indicate that in rat eyes SP and NKA are miotics, but the amounts that can be released from sensory nerve endings are too small to cause persistent miosis. These peptides are more likely to play a role in the neurogenic breakdown of the blood‐aqueous barrier. CGRP at the same dose affects neither the pupillary sphincter muscle no

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08252.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Duodenal HCO3‐secretion in anaesthetized rabbits was measured by continuous titration of the recirculating luminal perfusate at pH 7.4. The segment under study started 3–4 cm distal to the pylorus and was devoid of pancreatic and biliary HCO3‐secretion. On histological examination the submucosa was seen to contain Brunner's glands, mainly of a mucous type. Duodenum in rabbit secreted HCO3‐at a considerably higher basal rate (100–125μequiv h‐1cm‐1of intestine) than has previously been found in the rat, cat or dog. The cyclo‐oxygenase inhibitor indomethacin (20 mg kg‐1) reduced the secretion by 30%, while prostaglandin E2(5–80μm, luminal) caused a dose‐dependent increase. Prostaglandins thus seem to be important in regulation of duodenal HCO3‐secretion in the rabbit and may play a role in duodenal protection against acid. Carbachol (1 and 10μg kg‐1) and atropine (0.5 and 1 mg kg‐1) had no effects whereas hexamethonium (to mg kg‐1) caused a persistent decrease (25%) in secretion. Effects of electrical stimulation of the vagal nerves or injection of the alpha2‐adrenergic agonist clonidine markedly depended on the agent used for anaesthesia. In urethane‐anaesthetized animals, clonidine (0.75–75μg kg‐1) tended to increase the secretion whereas with nembutal, clonidine (5–150μg kg‐1) decreased it significantly. Electrical stimulation of the cervical vagal nerves decreased the HCO3‐secretion in urethane‐anaesthetized animals but had no significant effect during nembutal anaesthesia. The responses in the nembutal‐anaesthetized rabbit are similar

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08253.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The effect of weaning on plasma levels of insulin and glucagon as well as on plasma glucose levels was studied in sows after final weaning (all the piglets removed in week 5 of lactation) and fractionated weaning (7 out of 12 piglets removed in week 3 of lactation). Insulin levels rose from 24 ± 6 to 106 ± 22μU ml‐14 days after final weaning and from i i ± 1 to 128 ± 20μU ml‐17 days after fractionated weaning. Glucagon levels fell from 60 ± 20 and 42 ± 8 to 35 ± to and 24 ± 5 pM in the two groups, respectively. Plasma glucose levels increased from 4.5 ± 0.5 to 7.2 ± 1.2 mmafter fractionated weaning and remained unchanged after final weaning. One possible mechanism that can explain this pronounced insulin increase and decrease of glucagon is the elevation of plasma glucose, since milk is no longer emptied from the mammary gland and since insulin resistance occurs after weaning in rats. Another possible explanation could be a decreased number of insulin receptors in the mammary gland, since prolactin which is known to increase insulin receptors is decreased

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08254.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The aim of the present investigation was to study changes in insulin, glucagon and plasma glucose levels in response to suckling in lactating dogs. Blood samples were drawn from a peripheral vein during suckling in weeks 1 and 3 of lactation in 10 lactating beagles. Insulin‐ and glucagon‐like immunoreactivity (below referred to as insulin and glucagon) were determined by radio‐immunoassay, and plasma glucose levels by the glucose oxidase method. Insulin and glucagon levels rose following onset of suckling. However, only the rises recorded in week 3 of lactation were statistically significant. Plasma glucose levels were not affected. The mechansim by which suckling influences the levels of insulin and glucagon is not known. However, the release of both hormones is under vagal control and it is possible that touching of the teats reflexly elicits a vagally mediated release of these hormones. Alternatively, since oxytocin stimulates the secretion of insulin and glucagon, the effects might be secondary to the oxytocin released by suckling. The physiological function of the suckling‐related release of insulin may be to stimulate milk production. Furthermore, since glucagon is also released, each suckling period may be accompanied by a transfer of glucose to the mammary glands from other maternal

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08255.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY