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Biomedical subjects

A de Haan

Publications and source records attributed to A de Haan.

At least 19 recordsLinked to original sources
PubMed1992

The influence of different beta-blocking drugs on the peripheral circulation in Raynaud's phenomenon and in hypertension.

In a double-blind, randomized, placebo-controlled study, the authors investigated the effects of different beta-adrenoceptor blocking drugs on the peripheral circulation. A single intravenous injection of the nonselective beta-blocker propranolol (0.20 mg/kg), the beta 1-selective adrenoceptor blocker metoprolol (0.25 mg/kg), and the nonselective beta-blocker with partial agonistic activity (PAA) pindolol (0.04 mg/kg) and of placebo (saline) was given to eight patients with a primary Raynaud's phenomenon and to nine untreated patients with primary hypertension. The authors measured finger skin temperature (FST), and laser Doppler estimated finger skin blood flux (LDF) before, during, and after a standardized finger cooling test, performed 25 minutes after the administration of the drugs. In both patients groups propranolol, metoprolol, and pindolol had no significant effect on FST and LDF in the first 25 minutes after administration both in comparison to baseline value and to placebo. Also, no significant differences were found in the recoveries of FST and LDF after cold challenge between all drugs and placebo in both groups. The authors conclude that no adverse effect of any type of beta-adrenoceptor blocker in comparison to placebo could be detected after a single administration on both the baseline finger skin perfusion and the recovery after cold-induced vasoconstriction. In addition, the authors could not demonstrate a favorable effect of beta 1-selectivity or PAA in comparison to a nonselective beta-adrenoceptor blocker without PAA, in any group.

Adrenergic beta-Antagonists↗
PubMed1992

Muscle fatigue and efficiency in relation to interval duration of successive contractions.

The work output, energy consumption and efficiency during repetitive dynamic contractions were calculated for rat extensor digitorum longus muscle. The muscles performed 40 successive dynamic contractions at 37 degrees C (with occluded bloodflow) with interval durations of either 500, 250 or 167 ms. The muscle-tendon complexes were allowed to shorten at the velocity at which they could exert their highest power output (50 mm.s-1). Work output in the first contraction was the same among the three groups with different interval durations. The reduction in work output during the series of contractions differed among the groups, mainly in the last part of the exercise period. In the group with the longest interval duration, work output steadily decreased over the whole contraction period and at the end was approximately 72% of the output in the first contraction. In contrast, after the 30th contraction, work output decreased at a significantly higher rate of approximately 3% of each contraction in the groups with the intermediate and the shortest interval duration. After the last contraction, work output in these groups was approximately 52% of the work output in the first contraction. These differences in fatigue coincided with differences in the reduction in adenosine 5'-triphosphate and the production of inosine-5'-monophosphate. Total work output was not significantly different among the three groups with different interval durations, indicating that the different reductions in work output in the last contractions only had a minor influence on total work output of all 40 contractions. Also high-energy phosphate consumption and efficiency were not significantly different over these three exercise periods. Thus with the protocol used no interval dependent pattern of efficiency could be detected.

Adenosine Triphosphate↗
PubMed1992

The nucleotide sequence of the variable region in Trypanosoma brucei completes the sequence analysis of the maxicircle component of mitochondrial kinetoplast DNA.

The nucleotide sequence of two non-contiguous DNA fragments of 4.0 and 2.2 kb, respectively, of the kinetoplast maxicircle of Trypanosoma brucei brucei EATRO strain 427 has been determined, completing the sequence analysis of the so-called variable region (see also de Vries et al., 1988, Mol. Biochem. Parasitol. 27, 71-82). Analysis of the entire 8-kb variable region sequence revealed the presence of a 5.2-kb cluster of imperfect, tandemly repeated sequences, flanked by DNA of unique sequence. Both repetitive and unique DNA evolve rapidly, but comparison to the closely related strain EATRO 164 indicated that the repetitive cluster is more prone to sequence and size divergence. The variable region is transcribed into RNAs of varying lengths but appears to be devoid of genes encoding mitochondrial proteins or tRNAs, as judged from computer analysis. Moreover, genes that could encode guide RNAs involved in producing the known edited mitochondrial mRNA sequences are also absent. The repetitive DNA cluster within this region consists of 14 blocks each containing one 130 bp repeat and a variable number of 19 bp repeats. A duplicated sequence was identified (5'-GGGGTTGGTGT) which proved to be identical to the eleven 5'-terminal residues of the universal minicircle dodecamer involved in initiation of leading strand synthesis. This suggests a role for these sequences in the initiation of maxicircle DNA replication. With the data presented in this report, the nucleotide sequence analysis of the 23016 bp maxicircle of T. brucei brucei EATRO strain 427 has been completed.

Animals↗
PubMed1992

Growth-related change in specific force but not in specific power of rat fast skeletal muscle.

The effect of growth on the dynamic performance of rat medial gastrocnemius muscle was studied. From approximately 1.5 to 5 months of age specific force increased by 18%. Reductions were found in both optimal stimulation frequency (from 120 to 100 Hz) and optimal shortening velocity (by 16%) indicating that the fibres became slower. Specific power did not change during growth but was obtained at a lower shortening velocity. Possible mechanisms for the observed changes are discussed.

Aging↗
PubMed1992

The potentiating effect of prestretch on the contractile performance of rat gastrocnemius medialis muscle during subsequent shortening and isometric contractions.

The aim of the present study was to investigate the effect of an active stretch during the onset of a muscle contraction on subsequent active behaviour of the contractile machinery within an intact mammalian muscle-tendon complex. Muscle length and shortening velocity were studied because they may be important variables affecting this so-called prestretch effect. Seven gastrocnemius medialis (GM) muscles of the rat were examined. Tetanic, isovelocity shortening contractions from 3 mm above muscle optimum length (l0) to l0 - 2 mm, at velocities of 10-50 mm s-1 (dynamic experiments), were preceded by either an isometric contraction (PI) or an active stretch (PS). By imposing quick length decreases between the prephase and the concentric phase, all excess force generated in the prephase was instantaneously eliminated. This procedure only allowed small force changes during subsequent shortening (caused by the intrinsic properties of the contractile machinery). In this way, the influence of series elastic structures on subsequent muscle performance was minimized. Experiments were also performed at lengths ranging from l0 + 2.5 mm to l0 - 1.5 mm, keeping the length constant after the initial quick length changes (isometric experiments). For the dynamic experiments, enhancement of the performance of the contractile machinery (potentiation) was calculated as the ratio of the average force level over each millimetre of shortening during PS to that during PI conditions (PS/PI). For the isometric experiments, the PS/PI force ratio after 300 ms of stimulation was used. The main result of the present study confirmed results reported in the literature and experiments on isolated muscle fibres. For all conditions, a potentiation effect was found, ranging from about 2 to 16%. Muscle length appeared to have a large positive effect on the degree of potentiation. At the greatest lengths potentiation was largest, but at lengths below optimum a small effect was also found. A negative influence of shortening velocity was mainly present at increased muscle lengths (l0 + 2.5 mm and l0 + 1.5 mm). For the dynamic experiments, no interaction was found between the effects of muscle length and shortening velocity on potentiation. However, there was a clear difference between the isometric and dynamic responses: the dependence of potentiation on muscle length was significantly greater for the isometric contractions than for the dynamic ones. These isometric-dynamic differences indicate that the processes underlying prestretch effects operate differently under isometric and dynamic conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

Sequences of three dsRNAs associated with La France disease of the cultivated mushroom (Agaricus bisporus).

La France disease of the cultivated mushroom, Agaricus bisporus, is known to be associated with the presence of a number of dsRNA segments. The nucleotide sequences of the dsRNAs M2 (1.3 kb), M1 (1.55 kb) and L3 (2.8 kb), invariably associated with the disease, were determined. Putative coding sequences for proteins with molecular weights of 38, 40 and 87 kDa were found for M2, M1 and L3 dsRNAs, respectively. The average G + C content of these dsRNAs was 43%, close to that of A. bisporus nuclear DNA. The nucleotide sequences, as well as the amino acid sequences, appear to be unique, as no matching sequences could be found among databases. S3 dsRNA (0.39 kb), which is occasionally found in large amounts in diseased mushrooms, is an internally deleted variant of M2 dsRNA and is largely composed of the non-coding ends of that dsRNA.

Agaricus↗
PubMed1991

Influence of an active pre-stretch on fatigue of skeletal muscle.

In activities such as running, many muscles of the lower extremities appear to be actively stretched before they are allowed to shorten. In this study we investigated the effect of an active pre-stretch on the fatigability of muscles. Thus muscle contractions were compared in which shortening was preceded by an active isometric phase or by an active stretch. Rat medial gastrocnemius muscle-tendon complexes (with arrested blood flow) performed a series of ten repeated contractions (1.s-1) with either an active stretch or an isometric phase preceding the shortening. Contraction duration (0.45 s), and shortening duration (0.3 s), distance (6 mm) and velocity (20 mm.s-1) were the same in both types of contraction. Work output during the ten shortening phases was approximately 40% higher in the contractions with an active pre-stretch; in contrast, high-energy phosphate utilization was similar. Over the ten repeated contractions reduction of work output during the shortening phases of both types of contraction was similar in absolute terms (approx. 9.5 mJ). It is suggested that all the extra work performed during the shortening phases after a pre-stretch originated from sources other than cross-bridge cycling, which are hardly affected by fatigue. However, reduction of work output in relative terms, which is how the reduction is often expressed in voluntary exercise, was less after a pre-stretch (26% vs 32%), giving the impression of protection against fatigue by an active pre-stretch.

Animals↗
PubMed1991

Effect of shortening velocity on work output and energy cost during repeated contractions of the rat EDL muscle.

The effect of shortening velocity on the reduction in work output, energy consumption and efficiency during repetitive contractions has been determined in rat extensor digitorum longus muscle. Muscles in situ (with occluded blood flow, 37 degrees C) were stimulated to perform 40 successive contractions (at 4 Hz) with a total duration of the exercise period of 10 s and shortening velocities of either 25, 50 or 75 mm.s-1 (whole muscle-tendon complex). Care was taken that work output during the shortening phase of the first contraction was the same for the different velocities used. Total work output of the 40 contractions was not significantly different between the three groups with different shortening velocities; nor was there a significant difference in the high-energy phosphate consumption over this 10-s exercise period. However, when the ratio of total work output and total energy consumption was calculated a significantly higher efficiency (25-30% in comparison with the efficiency of the other two velocities) was found with the shortening velocity of 50 mm.s-1. There was no significant difference in efficiency between shortening velocities of 25 and 75 mm.s-1. This suggests that with this protocol efficiency showed a velocity-dependent pattern that may have the same shape as the power/velocity curve. Whereas total work output during the 10-s exercise period was not significantly different between the velocities studied, the time course of the changes in work output was quite different. With shortening velocities of 50 and 75 mm.s-1 work output initially increased by maximally 6% and 12% respectively in contrast to a steady level in the contractions with a velocity of 25 mm.s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

High-energy phosphates and fatigue during repeated dynamic contractions of rat muscle.

Reductions in work output during repeated contractions of rat medial gastrocnemius muscles (37 degrees C) were compared with changes in muscle metabolite concentrations. Three different exercise protocols were used in which the total number of stimuli and the length excursion were the same. The muscles performed a series of either 10, 25 or 40 repeated contractions at velocities of 20, 50 and 80 mm/s for groups A, B and C, respectively. In group A work output decreased steadily to 66% of the output in the first contraction. In groups B and C work output decreased to less than 10% of the first contraction. Changes in phosphocreatine and lactate concentrations were similar for all groups. However, very low ATP concentrations (approximately 35% of the resting value) were observed in groups B and C, compared with approximately 65% in group A. Inosine 5'-monophosphate (IMP) production was 9.9 mumol/g dry wt in group A and approximately 18 mumol/g dry wt in groups B and C. The results suggest fatigue does not depend on changes in intracellular inorganic phosphate and pH but possibly on changes in nucleotide metabolism.

Adenosine Triphosphate↗
PubMed1990

Effects of prestretch at the onset of stimulation on mechanical work output of rat medial gastrocnemius muscle-tendon complex.

Work output of rat gastrocnemius medialis (GM) muscle (N = 5) was measured for stretch-shortening contractions, in which initiation of stretch occurred prior to the onset of activation, and for contractions with an isometric prephase. Duration of the active prephase (prestretch and pre-isometric) varied from 20 to 200 ms. Subsequent shortening (from optimum length + 4 mm to optimum length -2mm) lasted 150 ms. Stretch velocities of 5, 10 and 20 mm s-1 were used, and the shortening velocity was 40 mm s-1. The effects of several combinations of active stretch duration and active stretch amplitude were compared. Using force-compliance characteristics, the work of the contractile element (CE), elastic energy storage and release of the undamped series elastic component (SEC) were distinguished. During shortening, an extra amount of work output was produced, induced by active stretch, of which the largest contribution (70-80%) was due to higher elastic energy release. Enhancement of the storage and utilization of elastic energy during the stretch-shortening cycle, caused by higher transition-point forces (i.e. force at onset of shortening), increased with active stretch amplitude and was associated with a net loss of work, probably due to cross-bridge detachment during active stretch. Net work over the stretch-shortening cycle remained positive for all prestretch contractions, indicating that when a muscle performs this type of contraction, it is able to contribute to work performance on body segments. It is concluded that, in stretch-shortening movements of rat GM muscle, maximal positive work output is incompatible with maximal net work output. Consequences for complex movements in vivo are discussed.

Animals↗
PubMed1989

Changes in velocity of shortening, power output and relaxation rate during fatigue of rat medial gastrocnemius muscle.

The force-velocity characteristics of rat medial gastrocnemius muscle have been determined by measuring the force sustained during constant velocity releases of the muscle stimulated in situ at an ambient temperature of 26 degrees C. The velocity of unloaded shortening was determined using the "slack" test and rate of relaxation from the half time of force loss at the end of stimulation. Measurements were first made on fresh muscles using short contractions and then during a series which consisted of a 15 s contraction (fatigued muscle), followed by 15 min recovery and a 1 s contraction (recovered muscle). After a 5 min recovery period the sequence was repeated. Comparison was made between the fatigued and recovered state in each preparation in order to allow for any change in the preparation during the course of the experiment. After 15 s contraction the fatigued muscles showed a marked reduction in all parameters measured. In fatigued muscles the isometric force fell to 48 +/- 15% (mean +/- SD) and there was a decrease in maximum velocity of shortening to 66%. These changes in the force-velocity relationship were accompanied by slowing of relaxation so that the half time of relaxation nearly doubled. The consequence of these changes was that the maximum power output was reduced by a much greater extent than was the isometric force (75% vs. 52%). It is suggested that the changes in force-velocity characteristics reflect a reduction in cross-bridge cycling in fatigued muscle.

Animals↗
PubMed1989

Age-related effects of fatigue and recovery from fatigue in rat medial gastrocnemius muscle.

Force-velocity, power-velocity and unloaded shortening data were obtained from in situ medial gastrocnemius muscle-tendon complexes (stimulated at 60 Hz) with intact circulation of mature male rats (approximately 125 days old). Measurements were carried out at the end of a long (15 s) contraction (fatigued muscles) or with a short (1 s) contraction either in the fresh state (fresh muscles) or in muscles which had recovered for 15 min after a long contraction. Compared to the fresh state fatigue reduced isometric force by 57%, maximal shortening velocity by approximately 40% and maximal power output by 81%. These reductions were similar to data previously obtained with younger rats (40 days old). However, the velocity data of the muscles which had recovered for 15 min after a long contraction showed a greater reduction in the mature rats. This difference between the two age groups together with a difference in the changes in the initial parts of the isometric force time curves suggest an age-dependent response of the fast-fatigable fibre population of these mixed muscles. In a separate series of experiments the underlying mechanism of the recovery from fatigue was studied in a group of young rats. Fatigue was induced with five long (15 s) contractions (each at 5 min intervals). The recovery of isometric force and power output was monitored with short contractions which indicated a plateau of recovery but the absolute values were still reduced after 60 min (85 and 71% of prefatigue values, respectively). Phosphocreatine concentration recovered rapidly, whereas the ATP concentration was still markedly reduced after 1 h of recovery. The time courses of recovery of inosine-5'-monophosphate (IMP) and lactate concentrations resembled those of force and power output. Thus it is possible that age-dependent differences in IMP and/or lactate production may play a role in fatigue and recovery from fatigue.

Adenosine Monophosphate↗
PubMed1988

Anaerobic chemical changes and mechanical output during isometric tetani of rat skeletal muscle in situ.

The time course was examined of the energy-rich phosphate usage and exerted isometric tetanic force in electrically stimulated rat quadriceps muscle. The maximal rate of energy-rich phosphate usage was calculated from the changes in the intramuscular concentrations of phosphocreatine, lactate, ATP and inosine monophosphate (IMP) and was somewhat higher than those calculated on the basis of exercise in vivo. The IMP concentration increased directly from the onset of the contraction until after about 11 s it remained constant. The increase in the IMP concentration coincided with a decrease in the ATP concentration. The relationship between mechanical output and energy usage was examined in two ways (i) by calculating the ratio time integral of the force (FTI) and the total energy-rich usage (Ptot) and (ii) by calculating the ratio Force (Ft) to the energy flux (dPtot/dt) at a certain time t. Whereas the ratio FTI/Ptot showed a hyperbolic relationship, the ratio Ft/(dPtot/dt) showed a parabolic relationship. From the latter finding and from the results described in the literature it is concluded that the ratio mechanical output/energy-rich phosphate usage depends on the conditions under which exercise is carried out. Recovery under aerobic conditions from a maximal tetanic isometric contraction sustained for 15 s was slow compared to results of experiments in vivo.

Anaerobiosis↗
PubMed1988

Age-related changes in power output during repetitive contractions of rat medial gastrocnemius muscle.

Changes in isometric force, power output and relaxation rate have been measured during repetitive tetanic contractions in 2 groups of rats of different ages. During the first 5 contractions there were no differences between a young and mature group. In contrast to isometric force production, which decreased about 3% per contraction, power output initially increased to 108% of the power output in the first contraction. A greater reduction in power output and relaxation rate after the 5th contraction indicated a greater reduction of the cross-bridge cycling rate in the younger rats. ATP, phosphocreatine and lactate concentrations after the last contraction were not different between the age-groups. In contrast IMP production, which has been suggested may play a regulatory role during fatigue was twice as high in the young rats. Judged by isometric force production there is no age-related difference in fatiguability. However, profound differences were observed in power output, which indicates that quantification of fatigue as a loss of isometric force may be seriously misleading when considering the functional status of the muscle for normal dynamic contractions.

Actins↗
PubMed1988

Influence of muscle dimensions on economy of isometric exercise in rat medial gastrocnemius muscles in situ.

The effect of muscle dimensions on economy (force-time integral divided by the amount of energy utilized) was investigated in male rats (body mass range 95-490 g), anaesthetized with pentobarbital. The medial gastrocnemius muscle in situ performed 6 maximal isometric contractions of 350 ms duration (1.s-1) at twitch optimum length at 35 degrees C. The areas under the 6 time-force curves were added to obtain force-time integral of the experiment. Differences of concentrations of ATP, phosphocreatine and lactate between experimental and contralateral (resting) muscles were used to calculate high-energy phosphate consumption due to stimulation. Muscle mass and cross-sectional area increased (approximately +400% and +300%, respectively) over the rat body mass range studied. Muscle length and length of the most distal fibre bundle increased by approximately 17 mm and 4 mm, respectively. Force-time integral (N.s) increased proportional to cross-sectional area whereas high-energy phosphate consumption (mumoles) increased proportional to muscle mass. The relative fraction of the total energy consumption utilized for force-independent processes was independent of rat body mass. The economy of the actomyosin system was unaffected during growth, whereas economy of the whole muscle decreased during growth by approximately 30% (p less than 0.001). The effect of muscle dimensions on economy is discussed with respect to human endurance capacity measured by voluntary isometric contractions.

Animals↗
PubMed1988

Comparison of force-velocity characteristics obtained using twitches and tetani from in situ rat skeletal muscles.

Force-velocity and power-velocity characteristics of three different rat skeletal muscle-tendon complexes (soleus, extensor digitorum longus and medial gastrocnemius) were obtained using twitch and tetanic contractions. No differences were found between twitches and tetani with respect to the shape of the force-velocity curves, or to the velocity at which the highest power output occurs. The results indicate that twitch contractions can be used to standardize muscle preparations in experiments aimed to study muscle energetics during dynamic contractions.

Animals↗
PubMed1988

Microbial production and metabolism of epoxides.

Epoxides are intermediates in the metabolism of many alkenes and aromatic compounds in higher organisms and in microorganisms. In microbial formation of epoxides, and further metabolism or excretion of these reactive compounds, many different enzymes are involved. Bacteria and fungi sometimes form optically active epoxides or are able to degrade epoxides enantioselectively, allowing the biotechnological production of these chiral building blocks in organic synthesis.

Bacteria↗