摘要:

The isolated rat hindquarter preparation perfused at constant flow was used to determine resistance and capacitance responses from pressure and weight recordings. In response to noradrenaline at low concentrations, the capacitance effect was greater than the relative increase in total vascular resistance. 8‐L‐Arginine vasopressin showed capacitance responses only when the resistance vessel constriction was pronounced. Oxytocin and two synthetic analogues, 2‐phenylalanine‐8‐ornithine vasopressin (Phe‐Orn‐VP) and 2‐phenylalanine‐8‐ornithine oxytocin, showed varying potency for resistance vessel constriction but hardly any capacitance responses. However, when Phe‐Orn‐VP induced a small increase in total vascular resistance, a marked increase in post‐capillary resistance was observed. The results are discussed in relation to a study in which the effects of vasopressin analogues were studied with intravital

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08900.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Variations in left ventricular (LV) wall tension during changes in LV end‐diastolic volume significantly affect myocardial oxygen consumption (MVO2). In the present study we examined if the reduction in MVO2) per beat accompanying a decline in LV end‐diastolic volume at constant LV systolic pressure (LVSP) is dependent on the level of myocardial inotropy. In six anaesthetized open‐chest pigs, the blood volume was expanded by i. v. infusion of a Ringer solution. At constant heart rate (by atrial pacing) and LVSP (by adjustments of a proximal aortic snare), LV end‐diastolic volume was reduced in steps by withdrawals of blood. This procedure was performed at high inotropy (during a continuous intracoronary infusion of isoproterenol, 0.40 ± 0.08 μg min‐1), and at low inotropy (after i. v. injection of 3.4 ± 0.2 mg propranolol).LVSP was about 25 mmHg higher at high than at low inotropy. The fall in LV tension was therefore greater during blood volume reductions at high than at low inotropy because the fall in LV end‐diastolic volume was almost identical and was initiated from the same level at both high and low inotropy. Nevertheless, the slope of the MVO2/LV end‐diastolic volume relationship was significantly (P<0.05) less steep at high (1.26 ± 0.30 μmol 100 g‐1mm‐1) than at low inotropy (2.06 ± 0.48 μmol 100 g‐1mm‐1). MVO2per beat fell by only 0.79 ± 0.17 μmol 100 g‐1(from 6.03 ± 0–4±5 μmol 100 g‐1= 13.8 ± 3.1%) at high inotropy compared with 1.21 ± 0.19 μmol 100 g‐1(from 3.79 ± 0.29 μmmol 100 g‐1= 30.5 ± 3.4%) at low inotropy.The greater reduction in MVO2per beat at low inotropy was associated with a reduction in LVdP/dtof 24 ± 4%, whereas LVdP/dtremained unchanged at high inotropy. Thus, the changes in MVO2per beat and LVdP/dtwere closely correlated (r= 0.94), and because the reduction in contractility was present only after propranolol administration it appeared to be induced by mechanisms

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08901.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Endothelin‐I (ET‐I), a peptide produced by the vascular endothelium, has been found to produce strong and persistent contractions of various blood vessels. In the present study, the effects of ET‐I were studied on isolated pulmonary arteries from four different levels (main pulmonary artery, large lobar arteries, small lobar arteries and intrasegmental arteries) of the guinea‐pig. In addition, the effects of ET‐I on pulmonary arteries were compared with those of pulmonary veins and trachea. ET‐I elicited a strong concentration‐dependent contraction of pulmonary arteries, veins and trachea. The effects of ET‐I were more pronounced in pulmonary arteries than in corresponding veins. Significant regional variations within the pulmonary arterial system were disclosed. The tracheal segments showed the same sensitivity and the same degree of relative maximal contraction as the pulmonary veins. Although the cellular mechanisms behind the action of ET still are not clear, our results favour a direct action of ET‐I on the vascular smooth muscle during vasoconstriction. Furthermore, the ET‐I‐induced contraction in guinea‐pig lung seems to be independent o

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08902.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The effects of endothelin, a vasoconstrictor peptide produced by vascular endothelial cells, were investigated in isolated rabbit and human corpus cavernosum (CC). Preparations from both rabbit and man were potently contracted by endothelin in a concentration‐dependent manner. The contractions developed slowly, could not be reversed despite frequent washings, and were only partly inhibited by the Ca2+channel blocker nimodipine. Even in Ca2+‐free medium containing the chelator EGTA a small contractile component persisted. In rabbit CC, the contractions in Ca2+‐free medium were not affected by nimodipine, the Ca2+‐channel agonist BAY K 8644, or by depletion of intracellular Ca2+stores sensitive to noradrenaline (NA) and caffeine, but were almost abolished by the protein kinase C inhibitor H7. In both rabbit and man, carbachol and vasoactive intestinal polypeptide concentration‐dependently relaxed preparations contracted by endothelin. The relaxations induced by carbachol were antagonized by atropine. Endothelin enhanced concentration‐dependently the contractions induced by exogenously applied NA in rabbit CC. The enhancement was more pronounced at low concentrations of NA.This study shows that endothelin potently contracts isolated penile erectile tissue. The contraction seems to be mediated mainly by influx of Ca2+through the cell membrane, which partly occurs through a pathway other than voltage‐operated calcium channels. However, involvement of other mechanisms cannot be excluded. The results suggest that endothelin can play a role in penile erecti

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08903.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The human trunk is a complex mechanical system comprised of large and small segments interconnected with several layers of muscles. An accurate control of this system is important during a variety of everyday tasks such as voluntary movements of the trunk, walking and running. This study was designed to investigate the interaction between muscles controlling the pelvis and the trunk during a variety of movements requiring a finely tuned coordination.Four subjects carried out seven different forms of fast oscillatory movements of the pelvis and trunk in the sagittal and transverse planes. Electromyographical activity (EMG) was recorded with surface electrodes from the abdominal muscles rectus abdominis (RA), obliquus externus (OE), obliquus internus (OI) and erector spinae (ES), from the hip flexor muscle rectus femoris (RF), the hip extensor muscle gluteus maximus (GM) and from the hip extensor/knee flexor muscles of the hamstrings group (HAM). Movements were recorded with an optoelectronic system (Selspot).The results indicate that during spontaneous flexion‐extension movements of the trunk there was a basic alternating activation between a pure flexor (RF‐RA‐OE‐OI) and an extensor synergy (ES‐GM‐HAM). Different mixed synergies appeared when more specific patterns of coordination of the pelvis and spine were performed. For example, during pelvic tilts in the sagittal plane, RA‐OE‐OI‐GM formed a synergy which was activated reciprocally with ES.The neural circuitry controlling muscles of the pelvis and trunk is apparently adaptable to a variety of different tasks. Individual muscles were shown to either cause, brake or prevent a movement and to be integrated in several different task‐specific motor synergies. Such a flexibility of the motor system is important for an accurate control of postural equilibrium and coordinative movements of t

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08904.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The effect of hydration status on plasma vasopressin release was studied in six healthy volunteers undergoing a 15‐min bicycle ergometer exercise. The hydration states were dehydration, produced by a 14‐h abstinence from fluids, euhydration, and hyperhydration caused by drinking 20 ml kg‐1water 2 h before the exercise. The exercise load was individually adjusted to 70% of maximal oxygen uptake. Exercise resulted in a significant increase in plasma vasopressin only during euhydration, in spite of the marked increase in plasma osmolality in all hydration states. The vasopressin concentrations during hyperhydration were significantly lower than during euhydration. Plasma volume and serum sodium were significantly affected by the exercise. The highest responses were obtained in euhydration and the lowest in hyperhydration. On this basis, the body's drive towards normal homeostasis and to the best ability to respond to the challenges of the environment is rat

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08905.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The activities of prolyl 4‐hydroxylase (PH) and galactosylhydroxylysyl glucosyl‐transferase (GGT), and the concentration of hydroxyproline (Hyp) were measured in the Achilles and tibialis anterior tendons of rats after periods of o, 3, 7 and 14 days remobilization following a 7‐day cast immobilization. PH, GGT and Hyp were also observed in the soleus and tibialis anterior muscles and the Achilles tendon 2, 5 and 10 days after a single bout of exhaustive exercise. During immobilization, the specific activity of PH decreased by 23% (P<0.05) and 54% (P<0.01) in the Achilles and tibialis anterior tendons. A less pronounced decrease was observed in GGT activity. During the remobilization experiment the specific activity of PH increased gradually, whereas GGT activity increased rapidly. The GGT activity was 61–66% (P<0.01) above the control value in the Achilles and tibialis anterior tendons after 3 days, decreasing to the control level after 14 days. Hyp concentration did not change significantly. In the exercise experiment, the specific activity of PH in the soleus muscle increased by 64% (P<0.05) 2 days after the prolonged exercise and then decreased gradually to the control level. There were no significant changes in PH or GGT activity in the tibialis anterior muscle. The specific activity of PH and GGT and Hyp concentration remained unchanged in the Achilles tendon. The results suggest that, in the tendon, restoring normal cage activity after immobilization results in acceleration of collagen synthesis. The results suggest also that collagen synthesis of the tendon is insensitive, but that of the soleus muscle is sensitive, to an acute increase in physical a

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08906.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

This study examined if there was a relationship between the aerobic‐oxidative potential of skeletal muscle and the metabolic and force recovery after intense exercise. Eleven male subjects performed three bouts of unilateral knee extensions using an isokinetic device. Sixty seconds of rest separated bouts. Muscle biopsies were taken from the vastus lateralis prior to exercise, immediately after bout 2 and before bout 3. Samples were analysed for adenosine triphosphate (ATP), adenosine diphosphate (ADP), inosine monophosphate (IMP), creatine phosphate (CP) and lactate contents and citrate synthase (CS) activity. Peak torque at the end of bout 2 was 45% of initial peak torque of bout 1 (IPT1). With recovery, initial peak torque of bout 3 (IPT3) was 81% of IPT1. Peak torque after recovery (IPT3/IPT1) was related to CS activity (r= 0.69). ATP, CP and ATP/ADP decreased with exercise. ADP, IMP and lactate increased. With recovery, ATP and CP remained depressed. IMP and lactate remained elevated. ATP/ADP and ADP returned towards ‘normal’, but only the latter attained resting levels. When analysing the individual responses the following correlations were found. After recovery, ATP/ADP (r= 0.57), ATP/ADP relative to rest (r= 0.71), lactate (r= ‐ 0.62), CP (r= 0.75) and CP relative to rest (r= 0.83) were related to CS activity. The changes in lactate (r= ‐ 0.76) and CP (r= 0.79) during recovery (bout 3 – bout 2) were also related to CS activity. The results suggest that the recovery of force and the ‘normalization’ of metabolite contents after short‐term, intense exercise are dependent on the aerobic‐oxidative potential of skeletal muscle. Thus, muscles with high CS activity showed marked decreases in lactate and increases in CP contents after recovery. A low CS activity, in contrast, was associated with no or only small recovery o

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08907.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Mechanical work, mechanical power, energy consumption and mechanical efficiency were studied in constant‐speed treadmill running of 5 min at seven different exercises around aerobic (AerT) and anaerobic (AnT) thresholds. The true efficiency of concentric (positive) mechanical work and gross efficiency of the whole body in seven male subjects were calculated. The total mechanical work was calculated from film through the translational, potential and rotational energy states as the sum of the changes of all the mechanical energy states in all body segments allowing energy transfer between segments and from energy state to state. The total energy consumption was measured by combining aerobic and anaerobic energy production in resting and working conditions. When the speed of the treadmill was increased from the velocity of 10 km h‐1(2.8 m s‐1) to 22 km h‐1(6.1 m s‐1), the concentric mechanical work per one step increased from 129 ± 45 J to 228 ± 82 J (P<0.01). Oxygen consumption increased from 2.22 ± 0.27 l min‐1to 4.47 ± 0.24 l min‐1. The amount of blood lactate increased from 0.94 ± 0.53 mmol l‐1at the lowest speed to 9.90 ± 2.89 mmol l‐1at the highest speed (P<0.001). The true efficiency of concentric work decreased from 74 ± 14% to 56 ± 8% (P<0.05). At the speed of the AerT, the economy of running, the vertical rise of different body segments and mechanical efficiency of positive work were high. The highest gross efficiency was found at the running speed

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08908.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The role of histamine H2‐receptors in cardiovascular control is unknown. In seven healthy volunteers, we studied how histamine H2‐receptor blockade affected the reflex response to hypovolaemia induced by lower‐body negative pressure (LBNP). In placebo‐treated individuals, LBNP down to ‐40 mmHg did not change systolic pressure but increased diastolic pressure, heart rate, forearm vascular resistance, plasma noradrenaline concentration and plasma renin activity. After pretreatment with ranitidine, a specific histamine H2‐receptor antagonist, the diastolic pressure rise no longer sufficed to maintain a constant systolic pressure during LBNP. Ranitidine pretreatment also attenuated the heart rate response and the rise in plasma renin activity induced by LBNP, but did not significantly change the reflex forearm vasoconstriction or the forearm plasma noradrenaline response.The results suggest that histamine H2‐receptor blockade attenuates the reflex vasoconstrictor response to lower‐body negative pressure. The mechanism behind this effect remains unknown, but the data do not support the idea that the effect is exerted in the skeletal musc

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1990.tb08909.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY