Biomedical subjects

O Hudlická

Publications and source records attributed to O Hudlická.

At least 19 recordsLinked to original sources

PubMed2003

Differences in local environment determine the site of physiological angiogenesis in rat skeletal muscle.

The specificity in location of angiogenesis to either glycolytic or oxidative fibre types, or muscle regions, was examined in the tibialis anterior (TA) and extensor digitorum longus (EDL) muscles of rat. Angiogenesis was induced by mechanical means either with (chronic muscle stimulation) or without (muscle stretch by overload) changes in blood flow, treatments which invoked only minor changes in fibre type and fibre size. Proliferation estimated by PCNA labelling of cells co-localised with capillaries was very rare in control muscles, where it occurred mainly in the glycolytic regions, but was increased in both models of angiogenesis. However, when labelled capillaries were scored according to the type of surrounding fibres, only muscle stimulation significantly accentuated proliferation of capillaries surrounded by glycolytic fibres. We conclude that while mechanical stimuli are important for proliferation in glycolytic regions in both models, capillary growth occurs specifically around glycolytic fibres in that region when the angiogenic stimulus includes increased blood flow and/or increased metabolic demand.

Adaptation, Physiological↗

PubMed2001

Unorthodox angiogenesis in skeletal muscle.

OBJECTIVE: The morphological pattern of angiogenesis occurring in mature, differentiated skeletal muscle in response to chronically increased muscle blood flow, muscle stretch or repetitious muscle contractions was examined to determine (a) whether capillary neoformation follows the generally accepted temporal paradigm, and (b) how the growth pattern is influenced by mechanical stimuli. METHODS: Adult rats were treated for a maximum of 14 days either with the vasodilator prazosin, to elevate skeletal muscle blood flow, or underwent surgical removal of one ankle flexor, to induce compensatory overload in the remaining muscles, or had muscles chronically stimulated by implanted electrodes. Extensor digitorum longus and/or extensor hallucis proprius muscles were removed at intervals and processed for electron microscopy. A systematic examination of capillaries and their ultrastructure characterised the sequence of morphological changes indicative of angiogenesis, i.e., basement membrane disruption, endothelial cell (EC) sprouting and proliferation [immunogold labelling after bromodeoxyuridine (BrdU) incorporation]. RESULTS: Capillary growth in response to increased blood flow occurred by luminal division without sprouting or basement membrane (BM) breakage. In stretched muscles, EC proliferation and abluminal sprouting gave rise to new capillaries, with BM loss only at sprout tips. These distinct mechanisms appear to be additive as in chronically stimulated muscles (increased blood flow with repetitive stretch and shortening during muscle contractions) both forms of capillary growth occurred. Endothelial cell numbers per capillary profile, mitotic EC nuclei, and BrdU labelling confirmed cell proliferation prior to overt angiogenesis. CONCLUSIONS: Physiological angiogenesis within adult skeletal muscle progresses by mechanisms that do not readily conform to the consensus view of capillary growth, derived mainly from observations made during development, pathological vessel growth, or from in vitro systems. The temporal and spatial pattern of growth is determined by the polarity of the mechanical stimulus, i.e., by intra-luminal (increased shear stress) or abluminal (external stretch) stimuli.

Analysis of Variance↗

PubMed2000

Effect of indomethacin on capillary growth and microvasculature in chronically stimulated rat skeletal muscles.

1. Capillary proliferation and microvessel diameters were studied in rat ankle flexors subjected to chronic electrical stimulation by implanted electrodes (10 Hz, 0.3 ms pulse width, up to 6 V, 8 h day-1) for 2 or 7 days with or without concurrent indomethacin treatment ( approximately 2 mg day-1 in drinking water) to study the role of prostaglandins in the microcirculation in relation to capillary growth. 2. Diameters of terminal arterioles, capillaries and confluent venules were measured in epi-illuminated muscles, together with capillary red cell velocity, to evaluate whether changes in capillary pressure and/or shear stress participate in capillary growth via release of prostaglandins. 3. Cell proliferation was detected following bromodeoxyuridine (BrdU) incorporation and immuno-staining of frozen sections. Labelling was assessed as the percentage of all interstitial nuclei (Haematoxylin-stained) that were BrdU positive. By comparison with serial sections stained for alkaline phosphatase, from which the capillary-to-fibre ratio (C:F) was obtained, labelling was derived for nuclei colocalised either to capillaries or to other non-capillary interstitial cells. 4. C:F increased to 1.89 +/- 0.06 from 1.47 +/- 0.04 in controls only after 7 days stimulation; indomethacin reduced this to 1.55 +/- 0.07. Capillary labelling increased from 2.9 +/- 0.5 % in controls to 11.3 +/- 2.2 % after 2 days stimulation and 10.6 +/- 0.8 % after 7 days. The increase was attenuated by indomethacin at both time points (to 5.8 +/- 1.6 % and 4.2 +/- 0.5 %, respectively). 5. Non-capillary interstitial labelling (2.0 +/- 0.4 % in controls) increased to 9.5 +/- 2.7 % after 2 days stimulation and was back to normal after 7 days (3.2 +/- 0.7 %). Indomethacin depressed the increase at 2 days to 4.0 +/- 1.3 % and had no effect at 7 days (2.9 +/- 0.13 %). Labelling in sham-operated rats with or without indomethacin or in vehicle-treated animals was no different from controls. 6. Arteriolar and venular diameters were increased by 2 days of stimulation but unchanged after 7 days. Indomethacin increased diameters of arterioles after 2 days and venules after 7 days in sham-operated animals, but had no effect on diameters of either vessel type in stimulated muscles. 7. Capillary diameters did not change during acute muscle contractions whereas red cell velocity did. Calculated shear stress in capillaries was thereby increased by 75 %. 8. Thus during chronic electrical stimulation both capillary growth and the cell proliferation that precedes it were attenuated by indomethacin. Transient stimulation-induced increases in arteriolar and venular diameters, which were unaffected by indomethacin, do not implicate increased capillary pressure as a factor in prostaglandin release and capillary growth. Estimations of increases in capillary shear stress during muscle contractions and of a 45 % higher value even at rest after chronic stimulation for 7 days suggest that shear stress is a more likely stimulus for prostaglandin release in chronically stimulated muscles.

Animals↗

PubMed2000

Inhibition of capillary growth in chronically stimulated rat muscles by N(G)-nitro-l-arginine, nitric oxide synthase inhibitor.

Shear stress causes release of nitric oxide (NO) from microvascular endothelial cells in vivo and stimulates their growth in vitro. After chronic electrical stimulation of lower hind limb skeletal muscles in the rat, measurements of capillary diameters and red blood cell velocity indicated that shear stress is increased in these vessels as a potential source of NO. This study therefore investigated whether NO is involved in capillary growth in stimulated muscles. Control rats or those stimulated for 2 or 7 days were treated with the NO synthase inhibitor, N(G)-nitro-l-arginine (l-NNA, 10 mg.day(-1) in drinking water), or water alone. After bromodeoxyuridine (BrdU) administration, extensor digitorum longus muscles were removed and frozen. Capillary supply was assessed in cryostat sections as capillary:fiber (C:F) ratio after staining for alkaline phosphatase; proliferation of capillary-linked and interstitial nuclei was evaluated by immunostaining for BrdU incorporation. C:F was not increased after 2 days of stimulation but the increase after 7 days (1.88 +/- 0.50 vs control 1.45 +/- 0.04, P < 0.001) was abolished by l-NNA (1.55 +/- 0.04, NS). The labeling index for BrdU-positive nuclei colocalized with capillaries as a percentage of total interstitial nuclei increased in muscles stimulated for 2 days (11.3 +/- 2.2%) and 7 days (10.6 +/- 0.8%) compared with controls (2.9 +/- 0.5%, P < 0.01) and was eliminated by l-NNA at both time points (3.1 +/- 0.6 and 1.0 +/- 0.6%, respectively; both P < 0.05 vs stimulated). A transient increase in BrdU labeling of interstitial nuclei not associated with capillaries (possibly fibroblasts) after 2 but not 7 days stimulation was eliminated by l-NNA treatment. These results suggest that NO is involved in capillary growth in chronically stimulated muscles possibly via its shear-stress-induced release from capillaries or from interstitial fibroblasts.

Animals↗

PubMed2000

The role of pericytes in controlling angiogenesis in vivo.

In order to evaluate the interaction between endothelial cells and the perivascular pericytes during physiological angiogenesis, stereological analysis of fine structure was performed on samples of rat skeletal muscle where capillary growth was induced to a similar extent by three different interventions (indirect electrical stimulation, vasodilatation by alpha 1-blockade, stretch due to synergist extirpation). There was a significant reduction in the relative area of contact between pericytes and the capillary abluminal surface with stimulation, and withdrawal of pericyte processes coincided with an increase in anatomical capillary supply. These data indicate that pericytes may play an anti-angiogenic role in vivo in normal adult tissue similar to that proposed for in vitro models of angiogenesis, with their retraction during increased muscle activity possibly releasing endothelial cells from their contact inhibition. However, following long-term peripheral vasodilatation expansion of the capillary bed was accompanied by a co-ordinated increase in pericytes, such that coverage of capillaries was similar to that in control muscles. In addition, growth of capillaries following prolonged stretch resulted in a slightly greater increase in the pericyte population, suggesting they may be permissive for endothelial cell migration. Thus, the role of pericytes in controlling physiological angiogenesis is dependent on the nature of the initial stimulus, suggesting that in vitro data have to be interpreted with caution when discussing the mechanism of capillary growth in vivo.

Animals↗

PubMed2000

Selective long-term electrical stimulation of fast glycolytic fibres increases capillary supply but not oxidative enzyme activity in rat skeletal muscles.

Glycolytic fibres in rat extensor digitorum longus (EDL) and tibialis anterior (TA) were selectively activated, as demonstrated by glycogen depletion, by indirect electrical stimulation via electrodes implanted in the vicinity of the peroneal nerve using high frequency (40 Hz) trains (250 ms at 1 Hz) and low voltage (threshold of palpable contractions). This regime was applied 10 times per day, each bout being of 15 min duration with 60 min recovery, for 2 weeks. Cryostat sections of muscles were stained for alkaline phosphatase to depict capillaries, succinate dehydrogenase (SDH) to demonstrate oxidative fibres, and periodic acid-Schiff reagent (PAS) to verify glycogen depletion. Specific activity of hexokinase (HK), 6-phosphofructokinase, pyruvate kinase, glycogen phosphorylase and cytochrome c oxidase (COX) were estimated separately in homogenates of the EDL and the predominantly glycolytic cortex and oxidative core of the TA. Stimulation increased the activity of HK but not that of oxidative enzymes in fast muscles. Comparison of changes in oxidative capacity and capillary supply showed a dissociation in the predominantly glycolytic TA cortex. Here, COX was 3.9+/-0.68 microM min(-1) (g wet wt)-1 in stimulated muscles compared with 3.7+/-0.52 microM min(-1) (g wet wt)-1 in contralateral muscles (difference not significant), while the percentage of oxidative fibres (those positively stained for SDH) was also similar in stimulated (14.0+/-2.8 %) and contralateral (12.2 +/-1.9 %) muscles. In contrast, the capillary to fibre ratio was significantly increased (2.01+/-0.12 vs. 1.55+/-0.04, P<0.01). We conclude that capillary supply can be increased independently of oxidative capacity, possibly due to haemodynamic factors, and serves metabolite removal to a greater extent than substrate delivery.

Animals↗

PubMed1999

Early changes in performance, blood flow and capillary fine structure in rat fast muscles induced by electrical stimulation.

1. Muscle blood flow, capillary fine structure and performance were investigated in the early stages of chronic indirect electrical stimulation of ankle flexors in the rat. 2. The fast muscles tibialis anterior (TA), extensor digitorum longus (EDL) and extensor hallucis proprius (EHP) were unilaterally stimulated via the right common peroneal nerve at 10 Hz and supramaximal voltage for 8 h a day for 2, 3 or 7 days and compared with muscles from control animals. 3. Muscle blood flow (MBF) was estimated at rest and during contractions by radioactive microspheres. It was higher at rest than in unstimulated controls only in muscles stimulated for 2 days; during contractions it was higher in some muscles stimulated for 3 days than in controls, and in all muscles by 7 days (192 +/- 17 vs. 149 +/- 12 ml (100 g)-1min-1 in controls). 4. Electron microscopical evaluation of individual capillaries in EHP fixed by superfusion in situ revealed thickening of capillary endothelium and decreased lumen volume in muscles stimulated for 7 (P < 0.005) but not 3 days. Significantly smaller capillary size indicates the presence of newly formed capillaries. 5. Isometric twitch tension, recorded from combined TA and EDL in stimulated and contralateral legs during 5 min contractions at 4 Hz, gradually declined from 175 +/- 9 to 99 +/- 4 kN m-2 after 7 days of stimulation (P < 0.05) while the fatigue index, calculated as (final twitch tension/peak twitch tension) x 100, increased from 69.8 +/- 3.4 to 90 +/- 3.0 % (P < 0. 05). No significant changes in the fatigue index occurred in muscles stimulated for 2 or 3 days. 6. Lower peak tension, but not fatigue index or MBF, was also observed in muscles contralateral to those stimulated for 3 and 7 days, which thus do not represent appropriate controls. 7. We conclude that the high resting blood flow found in muscles stimulated for 2 days may initiate the capillary growth reported previously, while the relatively modest increase in MBF during contractions in muscles that had been stimulated for 7 days may be due to increased capillary supply. Swelling of the capillary endothelium and decreased volume of the capillary lumen may result in an increased proportion of time spent by red blood cells in capillaries, which would improve oxygen extraction.

Animals↗

PubMed1999

Arteriolar reactivity and capillarization in chronically stimulated rat limb skeletal muscle post-MI.

The purpose of this study was to assess whether electrical stimulation-induced increases in muscular activity could improve capillary supply and correct previously documented abnormal vasodilator and vasoconstrictor responses of arterioles in limb skeletal muscle post-myocardial infarction (MI). Extensor digitorum longus (EDL) muscle from rats with surgically induced MI ( approximately 30% of the left ventricle) was chronically stimulated (Stim) 8 h/day for 6 +/- 1 days, at 11 wk post-MI. Third- (3A) and fourth-order (4A) arterioles in EDL from nine MI rats and four MI+Stim rats were compared with those of 11 controls (Con). Compared with Con rats, MI alone caused a reduction in the resting diameter of 3A and 4A arterioles, which was completely reversed by MI+Stim. However, Stim did not correct the attenuated vasodilator response to 10(-4) M adenosine seen in 4A arterioles from MI rats compared with Con. The constrictor response of both 3A and 4A vessels in MI rats to low doses of acetylcholine (10(-9) M, 10(-8) M) and norepinephrine (10(-9) M) was accentuated in MI+Stim. The proportion of oxidative fibers in EDL was unaffected by MI or MI+Stim combination. However, Stim significantly increased (P < 0.05) the capillary-to-fiber ratio in this muscle compared with Con. Thus, although the increase in muscle activity induced by chronic electrical stimulation normalized the reduction in resting vessel diameter seen after MI, it failed to correct the abnormalities in vasoreactivity of these same vessels.

Animals↗

PubMed1998

Internal division of capillaries in rat skeletal muscle in response to chronic vasodilator treatment with alpha1-antagonist prazosin.

Chronic vasodilatation represents a stimulus for capillary growth associated with increased luminal shear stress. We have examined the ultrastructure of more than 2000 capillaries to establish whether the sequence of angiogenesis in response to this stimulus is similar to that described during development and under pathological circumstances. Administration of the alpha1-blocker prazosin to rats for 2 weeks led to a greater capillary length density in extensor hallucis proprius muscles without any change in capillary tortuosity: Jv(c,f)=262+/-54 compared with 350+/-17 mm-2, control compared with prazosin (P<0.002). There were obvious signs of endothelial cell (EC) activation after prazosin treatment, including an increased proportion of capillaries with rough endoplasmic reticulum, large cytoplasmic vacuoles, thickened endothelium and an irregular luminal surface. Capillaries from control muscles had a maximum of three ECs in cross section, whereas four ECs were noted in 0.8+0.5% of capillaries after 1 week (n.s.) and 2.5+/-0.9% after 2 weeks (P<0.01) of treatment. This could be due to elongation and/or migration of ECs, as cell proliferation has not been described at these time points. There was also an increase in the proportion of capillaries having a narrow, slit-like lumen (1.7+/-0. 8% of controls; 7.1+/-1.9% at 1 week; 8.8+/-2.5% at 2 weeks; P<0.02), some of which were smaller in size (less than 2 microm diameter) than in controls (3-5 microm) and/or "seamless", i.e. lacking EC junctions. These may represent newly formed vessels. Focal discontinuity of the basement membrane and abluminal EC processes were rarely seen, and capillary growth by abluminal sprouting appeared to be very infrequent (less than 0.001% of profiles). Of more importance was growth starting from the luminal side. Significantly more thin cytoplasmic processes were observed protruding into the lumen of capillaries after 1 week (47.5+/-6.2%, P<0.001) and 2 weeks of prazosin (34.2+/-5.5%, P<0.05) than in control vessels (16.7+/-3.9%). Some of these traversed the entire lumen and connected with endothelium of the opposite side, probably involving membrane fusion, resulting in the appearance of a double lumen. Individual capillaries with a complete double lumen were observed after 2 weeks' prazosin but comparatively rarely, in only four out of six muscles. These findings indicate a pattern of luminal growth which is completely different from intussusceptive growth previously described during development, and from the abluminal capillary sprouting seen under pathological circumstances.

Adrenergic alpha-Antagonists↗

PubMed1998

The effect of alpha 1 adrenoceptor antagonist prazosin on capillary supply, blood flow and performance in a rat model of chronic muscle ischaemia.

OBJECTIVE: This study explores whether the a1 blocker prazosin improves capillarisation, blood flow and muscle performance in chronically ischaemic muscles. DESIGN: Rat skeletal muscles were made ischaemic by unilateral ligation of the common iliac artery. The animals received prazosin and muscle blood flow, performance and capillary supply were studied 2 or 5 weeks later. MATERIALS AND METHODS: Prazosin (50 mg/l) was given in drinking water to animals with limited or intact blood supply. Muscle isometric twitch tension and fatigue index and blood flow at rest and during contractions (estimated by radio labelled microspheres) were measured in tibialis anterior, TA, and extensor digitorum longus, EDL. Capillary supply (capillary/fibre ratio, C/F) was estimated in frozen muscle sections stained for alkaline phosphatase in TA, EDL and soleus, S. RESULTS: Prazosin increased significantly capillary supply in ischaemic muscles after 2 and 5 weeks and blood flow during contractions (control muscles 163 +/- 6 ml. 100 g-1 min-1; ligated 2 weeks 25 +/- 7, ligated +prazosin 116 +/- 38 ; ligated 5 weeks 27 +/- 7, +prazosin 137 +/- 29, p < 0.05 vs. ligated). Fatigue index (final/peak tension over 5 min contractions at 4 Hz in %) was significantly improved by prazosin after 2 weeks (FI = 69 +/- 3% controls, 35 +/- 4% ligation, 60 +/- 3% ligation +prazosin) and less after 5 weeks (52 +/- 12% ligation, 61 +/- 3% ligation +prazosin). In contrast, prazosin had no effect on muscle performance in normal muscles in spite of it increased C/F and blood flow. CONCLUSIONS: Alpha1 adrenoceptor blockade is an effective way for improvement of capillary supply, blood flow and muscle performance in ischaemic muscles; the effect on muscle performance is most pronounced 2 weeks after induction of ischaemia.

Adrenergic alpha-Antagonists↗

PubMed1998

Lack of involvement of basic fibroblast growth factor (FGF-2) in capillary growth in skeletal muscles exposed to long-term contractile activity.

Fibroblast growth factors (FGFs) are involved in stimulation of angiogenesis in tumors and other pathological circumstances. Increased activity of normal skeletal muscles resulting from chronic electrical stimulation is a very potent stimulus for capillary growth but a relationship between the initiation of this angiogenesis and the involvement of autocrine growth factors has yet to be established. Although FGF expression has been reported in muscles stimulated for 3 weeks, capillary growth is underway significantly earlier, beginning around 3 days. The present experiments have therefore studied the possible involvement of basic fibroblast growth factor (FGF-2) in stimulated rat fast skeletal muscles prior to, and coincident with, capillary growth. Muscle contractions were induced via electrodes implanted in the vicinity of the peroneal nerve and maintained for 8h/day for 2, 4 or 7 days. Capillary/fiber ratio (C/F), based on staining of capillary endothelium for alkaline phosphatase, was not changed in either extensor digitorum longus (EDL) or tibialis anterior (TA) after 2 days stimulation, but increased in TA stimulated for 4 days and in both muscles after 7 days. The expression of mRNA for FGF-2, detected by ribonuclease protection assay, was decreased in all stimulated muscles compared with control or contralateral muscles; immunohistochemistry showed FGF-2 gene product in nerves and larger blood vessels but not in capillaries. There was no evidence from immunohistochemistry for up-regulation of receptors flg and bek for FGF-2. The presence of FGF-2, flg and bek in arterioles may indicate a possible role for FGF-2 in the regulation of blood flow since we have previously shown it to be a dilator of small arterioles. However, based on the lack of correlation between changes in capillary density and the expression of mRNA and protein for FGF-2 and its receptors, it is unlikely that it is directly linked with the initiation of angiogenesis resulting from chronic activity in skeletal muscles.

Journal Article↗

PubMed1998

Capillary growth in relation to blood flow and performance in overloaded rat skeletal muscle.

Rat extensor digitorum longus muscles were overloaded by stretch after removal of the synergist tibialis anterior muscle to determine the relationship between capillary growth, muscle blood flow, and presence of growth factors. After 2 wk, sarcomere length increased from 2.4 to 2.9 micrometers. Capillary-to-fiber ratio, estimated from alkaline phosphatase-stained frozen sections, was increased by 33% (P < 0.0001) and 60% (P < 0.01), compared with control muscles (1.44 +/- 0.06) after 2 and 8 wk, respectively. At 2 wk, the increased capillary-to-fiber ratio was not associated with any changes in mRNA for basic fibroblast growth factor (FGF-2) or its protein distribution. FGF-2 immunoreactivity was present in nerves and large blood vessels but was negative in capillaries, whereas the activity of low-molecular endothelial-cell-stimulating angiogenic factor (ESAF) was 50% higher in stretched muscles. Muscle blood flows measured by radiolabeled microspheres during contractions were not significantly different after 2 or 8 wk (132 +/- 37 and 177 +/- 22 ml. min-1. 100 g-1, respectively) from weight-matched controls (156 +/- 12 and 150 +/- 10 ml. min-1. 100 g-1, respectively). Resistance to fatigue during 5-min isometric contractions (final/peak tension x 100) was similar in 2-wk overloaded and contralateral muscles (85 vs. 80%) and enhanced after 8 wk to 92%, compared with 77% in contralateral muscles and 67% in controls. We conclude that increased blood flow cannot be responsible for initiating expansion of the capillary bed, nor does it explain the reduced fatigue within overloaded muscles. However, stretch can present a mechanical stimulus to capillary growth, acting either directly on the capillary abluminal surface or by upregulating ESAF, but not FGF-2, in the extracellular matrix.

Animals↗

PubMed1994

Iloprost reduces leukocyte adhesion in skeletal muscle venules following ischaemia in a rat model of femorodistal bypass.

UNLABELLED: Intraarterial bolus treatment with the prostacyclin analogue iloprost appears to have a prolonged beneficial effect on femorodistal bypass graft flow which extends beyond the duration of its vasodilator properties. The effect of iloprost on the microcirculation rendered ischaemic over the time course of a distal bypass operation was investigated in this study without the use of fluorescent light. METHODS: A rat model was designed to allow prolonged direct observation of leukocyte-venular endothelial adhesion in a femorodistal bypass simulation. The extensor digitorum longus (EDL) muscle of 10 rats was subjected to two 30 minute periods of ischaemia by a non-venous occluding tourniquet and to simulate some of the changes of chronic ischaemia the adverse effect of ischaemia was accentuated by indirect electrical stimulation via the lateral popliteal nerve. RESULTS: Intraarterial bolus treatment with iloprost significantly reduced the total numbers of leukocytes observed in EDL venules, and the numbers exhibiting evidence of adhesion by rolling or sticking to venule endothelium compared with saline controls at one hour post ischaemia. Ischaemia induced vasodilatation and reduced shear stress by a similar and significant amount in both groups. CONCLUSION: Two periods of ischaemia and reperfusion similar to those which occur during bypass grafting resulted in changes in the distal microcirculation consistent with reperfusion injury. Intraarterial bolus treatment with iloprost prevented these leucocyte-endothelial changes. It appears iloprost may have a role in reducing leukocyte-induced reperfusion injury in femorodistal bypass surgery.

Animals↗

PubMed1991

The effect of torbafylline on enzyme activities in fast and slow muscles with limited blood supply.

1. Activities of a glycolytic enzyme--lactate dehydrogenase, LDH, and two oxidative enzymes--citrate synthase (CS), a marker for TCA cycle entry, and 3-hydroxyacyl-CoA dehydrogenase (HAD), which indicates the capacity for beta-oxidation of endogenous lipids, were measured in fast (tibialis anterior, TA, and extensor digitorum longus, EDL) and slow (soleus, SOL) muscles of Sprague-Dawley rats with intact and limited blood supply, and following treatment with the xanthine derivative torbafylline (Hoechst, Werk Albert, Wiesbaden). 2. Limitation of blood supply by unilateral ligation of the common iliac artery increased activity of LDH in fast muscles, and activity of CS and HAD in soleus. 3. Torbafylline treatment caused an increased LDH activity in intact fast muscles and decreased it in soleus, although the relative capacity for anaerobic and aerobic metabolism (indicated by the ratio of LDH and CS activities) remained unchanged in all cases. 4. Whilst having little effect on oxidative enzyme activity of fast muscles, torbafylline decreased the activity of CS but increased activity of HAD in soleus, suggesting a greater reliance on lipid metabolism. 5. The effect of arterial ligation on enzyme activity was ameliorated by treatment with torbafylline, possibly due to its effect on the microcirculation.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed1990

Changes in capillary perfusion induced by different patterns of activity in rat skeletal muscle.

The proportion of "perfused" capillaries was evaluated in rat tibialis anterior at rest and during two different types of contraction after timed injection of thioflavine S. Capillary/fibre (C/F) ratio was estimated for "perfused" capillaries--those filled with fluorochrome--(Cp) from photomicrographs. Sections were subsequently stained for alkaline phosphatase and C/F ratio was estimated for all capillaries (Ct). At 7.5 sec after injection of fluorochrome, Cp:Ct at rest was 0.32 +/- 0.092 in the oxidative core and 0.43 +/- 0.058 in the glycolytic cortex (means +/- SEM). This increased to 0.83 +/- 0.045 and 0.88 +/- 0.026, respectively, during selective activation of glycolytic fibres. Activation of all fibres led to a modest further increase (0.92 +/- 0.040 in the core and 0.91 +/- 0.035 in the cortex). Blood flow (measured by radiolabelled microspheres increased to a similar extent (fivefold) in both regions of the muscle during activation of glycolytic fibres; the further increase during maximal activation was much smaller in the cortex (from 4 to 41 ml/100 g/min) than in the core (from 7 to 196 ml/100 g/min). Increased capillary perfusion during muscle contractions was thus independent of the type of activity, while muscle blood flow increased more in oxidative than in glycolytic regions during maximal activation. Thus the increase in muscle blood flow with maximal activation cannot be accounted for by further recruitment of "unperfused" capillaries and must result from a significant increase in the velocity of capillary blood flow.

Animals↗

PubMed1990

Effects of torbafylline, pentoxifylline and buflomedil on vascularisation and fibre type of rat skeletal muscles subjected to limited blood supply.

1. Blood flow (measured by radio-labelled microspheres), fibre composition and capillary/fibre ratio were estimated in rat fast twitch skeletal muscles (tibialis anterior and extensor digitorum longus) five weeks after unilateral ligation of the common iliac artery in animals treated with either saline, torbafylline, pentoxifylline or buflomedil. 2. The resting blood flow was lower in muscles with limited blood supply than in their contralateral controls; this difference became statistically insignificant after treatment. Capillary/fibre ratio was similar in all muscles with either intact or limited blood supply and did not change after administration of any of the drugs. 3. The percentage of glycolytic fibres was not changed by ligation, but it decreased significantly in animals treated with torbafylline. This may improve performance in muscles with limited blood supply.

Animals↗

PubMed1990

Substance P is released from the endothelium of normal and capsaicin-treated rat hind-limb vasculature, in vivo, by increased flow.

The rat hind-limb vasculature releases substance P when subjected to a rapid increase in flow through the vascular bed. This release also occurs during high flow after rats have been capsaicinized, when loss of substance P-containing nerve fibers was verified by immunohistochemistry. Air treatment, a procedure shown by transmission electron microscopy to have removed endothelial cells from the arteries but not arterioles or capillaries of the hind-limb preparations, eliminated this release. Thus, the substance P released is unlikely to arise from perivascular nerves but rather from arterial endothelial cells.

Animals↗

PubMed1989

The effects of long term administration of prazosin on the microcirculation in skeletal muscles.

The effect on the microcirculation of long term administration of the alpha 1 blocker prazosin, which increases peripheral blood flow, was studied in skeletal muscles with differing metabolic profiles. Prazosin (50 mg.litre-1), given ad libitum for 5 weeks in the drinking water, resulted in an increase in capillarity in both fast glycolytic tibialis anterior cortex and slow oxidative soleus muscles of the rat. In tibialis anterior, the velocity of red blood cells through capillaries was increased, a smaller proportion of capillaries had intermittent flow, less time was spent stationary by red blood cells, and hence the calculated volume flow per capillary was increased. In soleus, capillary diameters were larger, but velocity, intermittency and calculated volume flow were unchanged. Therefore, suggested mechanisms for capillary growth induced by prazosin are different for the two muscles studied: increased shear stress and blood/endothelial cell interaction in the case of tibialis anterior, and increased capillary wall tension in the soleus.

Animals↗