Biomedical subjects

S Egginton

Publications and source records attributed to S Egginton.

At least 19 recordsLinked to original sources

PubMed2003

The effect of chronic skeletal muscle stimulation on capillary growth in the rat: are sensory nerve fibres involved?

Indirect chronic electrical stimulation of skeletal muscle activates not only efferent but also afferent nerve fibres. To investigate effects specific to this on capillary growth, one of the earliest changes, cell proliferation and capillary ultrastructure were studied in ankle flexors of rats with and without deafferentation of the stimulated side. Two weeks after preganglionic section of dorsal roots L4-L6, the peroneal nerve was stimulated (10 Hz, 8 h day(-1)) for 2 or 7 days. Proliferating nuclei labelled by bromodeoxyuridine or proliferating cell nuclear antigen staining were colocalized to alkaline phosphatase-stained capillaries (Lc) or other interstitial nuclei (Li) in frozen sections of extensor digitorum longus. Capillary fine structure was examined in extensor hallucis proprius by transmission electron microscopy. The stimulation-induced increase in capillary and interstitial proliferation (Lc 9.9 +/- 1.9 %, Li 8.8 +/- 2.1 % vs. Lc 2.6 +/- 0.4 %, Li 1.9 +/- 0.3 % in controls, P < 0.05) was depressed at 2 days by dorsal root section (Lc 4.8 +/- 0.7 %, Li 3.2 +/- 0.9 %, P < 0.05), an effect likely to be mainly on fibroblasts; no depression was seen at 7 days. Dorsal root section reduced stimulation-induced capillary endothelial swelling at both time points. In contralateral muscles of intact rats, stimulation increased interstitial cell proliferation and capillary swelling, both effects being eliminated by dorsal root section. Capillary growth induced by stimulation (24 % increase in capillary : fibre ratio at 7 days) was unaffected by deafferentation. The reduction in capillary ultrastructural changes and interstitial proliferation in both stimulated and contralateral muscles implies that stimulation of afferent fibres leads directly to release of humoral factors and/or activation via dorsal roots of fibres that release humoral substances. Contralateral muscles are an inadequate control for the effects of chronic stimulation in the intact animal.

Alkaline Phosphatase↗

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↗

PubMed2003

Muscle fine structure may maintain the function of oxidative fibres in haemoglobinless Antarctic fishes.

Muscle fine structure and metabolism were examined in four species of Antarctic fishes that vary in their expression of haemoglobin (Hb). To determine how locomotory pectoral muscles maintain function, metabolic capacity, capillary supply and fibre ultrastructure were examined in two nototheniid species that express Hb (Notothenia coriiceps and Gobionotothen gibberifrons) and two species of channichthyid icefish that lack Hb (Chaenocephalus aceratus and Chionodraco rastrospinosus). Surprisingly, icefish have higher densities of mitochondria than red-blooded species (C. aceratus, 53+/-3% of cell volume; C. rastrospinosus, 39+/-3%; N. coriiceps, 29+/-3%; G. gibberifrons, 25+/-1%). Despite higher mitochondrial densities the aerobic metabolic capacities per g wet mass, estimated from measurements of maximal activities of key metabolic enzymes, are lower in icefish compared to red-blooded species. This apparent incongruity can be explained by the significantly lower mitochondrial cristae surface area per unit mitochondrion volume in icefishes (C. aceratus, 20.8+/-1.6 microm(-1); C. rastrospinosus, 25.5+/-1.8 microm(-1)) compared to red-blooded species (N. coriiceps, 33.6+/-3.0 microm(-1); G. gibberifrons, 37.7+/-3.6 microm(-1)). Consequently, the cristae surface area per unit muscle mass is conserved at approximately 9 m(2)g(-1). Although high mitochondrial densities in icefish muscle do not enhance aerobic metabolic capacity, they may facilitate intracellular oxygen movement because oxygen is more soluble in lipid, including the hydrocarbon core of intracellular membrane systems, than in aqueous cytoplasm. This may be particularly vital in icefish, which have larger oxidative muscle fibres compared to red-blooded nototheniods (C. aceratus, 2932+/-428 microm(2); C. rastrospinosus, 9352+/-318 microm(2); N. coriiceps, 1843+/-312 microm(2); G. gibberifrons, 2103+/-194 microm(2)). These large fibres contribute to a relatively low capillary density, which is partially compensated for in icefish by a high index of tortuosity in the capillary bed (C. aceratus=1.4, N. coriiceps=1.1).

Aerobiosis↗

PubMed2002

Muscle ischaemia in rats may be relieved by overload-induced angiogenesis.

Alleviation of muscle ischaemia by improving capillary supply has proved difficult, possibly reflecting the inability to substantially increase blood flow. We reasoned that muscle overload, which induces angiogenesis in the absence of altered blood flow, may be an alternative to drug therapy. Male Wistar rats underwent unilateral ligation of the common iliac artery, with or without ipsilateral extirpation of the tibialis anterior muscle. Six weeks later ischaemic (I) extensor digitorum longus (EDL) had a 10% (P < 0.05) decrease in relative muscle mass, while overloaded muscles (O) had undergone hypertrophy of 39% and 52% relative to contralateral (CL) and control (C) muscle masses, respectively (P < 0.01). Muscle atrophy was prevented by the combination of overload and ischaemia (O/I), with hypertrophy of 24% (vs. CL) and 35% (vs. C), respectively (P < 0.01). Changes in muscle fibre cross-sectional area paralleled the changes in muscle mass, with means of 1898 +/- 59, 1531 +/- 90, 2253 +/- 155 and 2292 +/- 80 mm2 for C, I, O and O/I, respectively (P < 0.01 vs. C and I). Capillary to fibre ratio (C:F) was significantly increased in overloaded (2.58 +/- 0.09) compared to contralateral (1.78 +/- 0.04), control (1.61 +/- 0.05) and ischaemic (1.73 +/- 0.06) muscles (P < 0.001). A similar increase in C:F was seen in overloaded plus ischaemic muscle (2.59 +/- 0.07) compared to contralateral (1.40 +/- 0.01) and control or ischaemic values (P < 0.01). In both O and O/I muscle groups, C:F and capillary density (CD) increased most in the region of EDL where fibre size was largest, while hypertrophy of fibres was least in the same region for both groups. These data suggest that the microvascular deficit evident in chronic muscle ischaemia may be alleviated by angiogenesis that is induced by mechanical stimuli via chronic muscle overload.

Animals↗

PubMed2002

Chronic hypoxia induces prolonged angiogenesis in skeletal muscles of rat.

Skeletal muscle capillarity and fibre cross-sectional area were investigated within and between diaphragm (Diaph), extensor digitorum longus (EDL), soleus (SOL) and tibialis anterior (TA) muscles of control and chronic hypoxic (12 % O(2) for 6 weeks) adult male Wistar rats (final body mass approximately 355 g). Cryostat sections were stained for alkaline phosphatase activity to depict all capillaries, and for succinic dehydrogenase to demonstrate regional differences in oxidative capacity within the muscles. Hypoxia-induced angiogenesis occurred in all muscles (P < 0.01), with capillary-to-fibre ratio (C:F) being higher in the more active and oxidative muscles, Diaph (27 %) and SOL (26 %), than phasically active and glycolytic muscles, TA (21 %) and EDL (15 %). Diaph, SOL and EDL maintained fibre size, and hence showed an increased capillary density (CD) and reduced intramuscular diffusion distance (DD), whereas TA showed fibre hypertrophy and maintained CD and DD compared to control muscles. The extent of angiogenesis among different regions of muscle varied so as to suggest that muscle fibre size has an additional influence on capillary growth during chronic systemic hypoxia, which is progressive over an extended period of systemic hypoxia.

Animals↗

PubMed2002

Peripheral oxygen transport in skeletal muscle of Antarctic and sub-Antarctic notothenioid fish.

Transcellular oxygen flux was modelled mathematically in the aerobic skeletal muscles of perciform fish species living at widely different temperatures (Antarctica, sub-Antarctica and the Mediterranean Sea). Using structural data derived from stereological analysis of electron micrographs, mean fibre P(O(2)) was calculated on the basis of temperature-corrected rates of mitochondrial respiration and oxygen diffusion. The mean muscle fibre diameter (MFD) among Antarctic notothenioids was in the range 17-61 microm and mitochondrial volume density, Vv(mit,f), was 0.27-0.53, but capillary-to-fibre ratio varied only between 1.2 and 1.5. For a mean capillary P(O(2)) of 6 kPa, the model predicted a mean tissue P(O(2)) in the range 0.7-5.8 kPa at the estimated maximum aerobic capacity (M(O(2)max)). The lowest levels of tissue oxygenation were found in the pectoral muscle fibres of the icefish Chaenocephalus aceratus, which lacks the respiratory pigments haemoglobin and myoglobin. Red-blooded notothenioids found in the sub-Antarctic had a similar muscle fine structure to those caught south of the Antarctic Convergence, with an MFD of 20-41 microm and Vv(mit,f) of 0.27-0.33, resulting in an estimated mean P(O(2)) of 4-5 kPa at M(O(2)max). Mean tissue P(O(2)) in the sub-Antarctic icefish Champsocephalus esox, with greater MFD and Vv(mit,f), 56 microm and 0.51, respectively, was calculated to exceed 1 kPa at winter temperatures (4 degrees C), although oxidative metabolism was predicted to be impaired at the summer maximum of 10 degrees C. At the high end of the thermal range, related perciform species from the Mediterranean had a negligible drop in intracellular P(O(2)) across their small-diameter fibres, to a minimum of 5.4 kPa, comparable with that predicted for Trematomus newnesi from the Antarctic (5.6 kPa) with a similar MFD. These data suggest that, within a single phylogenetic group, integrative structural adaptations potentially enable a similar degree of tissue oxygenation over a 20 degrees C range of environmental temperature in the red-blooded notothenioids, and that this is compromised by the lack of respiratory pigments in the icefishes. The mean capillary radius was 1.5 times greater in the two icefish than in the other notothenioids, and the model simulations indicate that the evolution of wide-bore capillaries is essential to maintain tissue oxygenation in the absence of respiratory pigments.

Animals↗

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↗

PubMed2001

Growth of arterioles precedes that of capillaries in stretch-induced angiogenesis in skeletal muscle.

Arteriolar growth accompanying capillary angiogenesis has been linked with hemodynamic factors resulting from increased blood flow. Here we describe the growth of arterioles occurring in rat skeletal muscles stretched by an overload due to the removal of agonist muscles, where blood flow was not increased, and we provide morphological evidence for the type of cells involved in this growth. Rat extensor digitorum longus (EDL) and extensor hallucis proprius (EHP) were overloaded by unilateral extirpation of their agonist, tibialis anterior. EDL muscles were taken for immunohistochemistry in cryostat sections to mark endothelial cells (Griffonia simplicifolia I, GSI lectin), smooth muscle cells and pericytes (alpha smooth muscle actin, alphaSMA), and "mature" arterioles (smooth muscle myosin heavy chains). EHP muscles were used for corresponding evaluation by confocal and electron microscopy. The number of capillaries surrounding muscle fibers was not significantly different after 1 week of stretch but was higher after 2 weeks (5.15 +/- 0.2 vs 4.3 +/- 0.2 in controls, P < 0.05). Similarly, capillary density (CD) and capillary/fiber ratio (C/F) gradually increased (CD 778 +/- 86 at 2 weeks vs 593 +/- 35 mm(-2) in controls, C/F 2.07 +/- 0.13 vs 1.38 +/- 0.06, respectively). In contrast, the number of alphaSMA-positive vessels around fibers increased after 1 week (2.16 +/- 0.09 vs 0.25 +/- 0.02 in controls) and was lower after 2 weeks (1.42 +/- 0.24, P < 0.05, vs 1 week). Arteriolar density was higher at 1 (110.9 +/- 7.5 mm(-2)) and 2 weeks (70.7 +/- 12.1) with respect to controls (31.0 +/- 1.6 mm(-2)). The increased density was greater in alphaSMA-positive vessels <10 microm in diameter (controls 18.0 +/- 1.04, 1 week 77.2 +/- 4.5, 2 wk 42.2 +/- 9.0 mm(-2)) than in vessels >10 microm (13.0 +/- 0.8, 33.7 +/- 4.0, 29.5 +/- 4.7 mm(-2)). Electron microscopy showed "activated" (TEM fine structure) and proliferating (immunogold labeling for BrdU) fibroblasts in the vicinity of capillaries, some of which were embedded in the capillary basement membrane, consistent with a transformation into pericytes and possibly later smooth muscle cells. Confocal microscopy indicated that some mesenchymal cells became GSI positive and formed extended processes which contacted capillaries via tapered endings. Growth of arterioles in stretched muscles appears to involve proliferation of fibroblasts, which may migrate toward capillaries and precedes any apparent increase in capillarization.

Animals↗

PubMed2001

Differential effect of cold acclimation on blood composition in rats and hamsters.

Male rats and hamsters were exposed to a progressively lower air temperature and shorter photoperiod to simulate the onset of winter. Normothermic hamsters had a higher haematological oxygen carrying capacity (OCC) and coagulability (shorter prothrombin time and activated partial thromboplastin time) than rats. Cold acclimation significantly increased the OCC of rats, which parallels an increased metabolic rate, while no differences were observed in hamsters. Red cell transit time through filters was faster in the acclimated rats but not in hamsters, reflecting the lower mean cell volume due to a decreased rate of clearance from the circulation. Platelet counts were significantly lower in both cold-acclimated rats and hamsters, and there was a significant leucopenia in rats, which would reduce the degree of microvascular blockade. Whole blood viscosity, plasma viscosity, and serum osmolarity showed little change in either species. However, whole blood viscosity was significantly lower in cold-acclimated hamsters than control hamsters at the lowest shear rate tested (0.95 s(-1)). Interestingly, plasma viscosity and serum osmolarity were significantly lower in hamsters exposed to low temperatures for a shorter period (4 weeks), and may reflect the development of a reduced coagulability. These data suggest that blood composition in hamsters contributes to an innate tolerance of low temperatures, maintaining tissue perfusion under hypothermic conditions and aiding arousal from hibernation.

Acclimatization↗

PubMed2001

Changes in the mechanical and adhesive behaviour of human neutrophils on cooling in vitro.

Changes in the rheological properties of neutrophils may influence flow in microvessels that are cooled below normal body temperature. We investigated the effects of temperature on the mechanical and adhesive properties of human neutrophils by measuring transit times for individual cells flowing through 8-microm-pores in filters, and adhesion to P-selectin for cells perfused over a monolayer of activated platelets. Pore transit time increased as temperature was decreased from 37 degrees C to 0 degrees C. Upon rapid cooling, there was an instantaneous increase attributable to changes in aqueous viscosity. Interestingly, at 10 degrees C specifically, there was an additional increase in transit time, which was abolished by the inhibitor of actin polymerization, cytochalasin B. This meant that by 15 min, transit time at 10 degrees C was greater than at 0 degrees C. Most adherent cells on P-selectin were rolling, rather than stationary, at 10, 26 or 37 degrees C. The velocity of rolling slowed with decreasing temperature. The total number of adherent cells decreased with increasing wall shear rate, but for a given shear rate there was relatively little effect of temperature on attachment. However, when adhesion at 10, 26 or 37 degrees C was compared at equal shear stress (taking into account fluid viscosity), adhesion was greatest at 10 degrees C. Measurements of immunofluorescence showed that exposure to 10 degrees C gradually increased expression of beta2-integrin CD11b/CD18, but this did not cause transformation to stationary adhesion with time in the flow assay. Thus, neutrophils show an anomalous rheological response around 10 degrees C, which may impair local microcirculation in the cold. On rewarming, "activated" cells might inhibit recovery or become released into the systemic circulation.

Adenosine Triphosphate↗

PubMed2001

Association between shear stress, angiogenesis, and VEGF in skeletal muscles in vivo.

OBJECTIVE: To investigate the hypothesis that capillary proliferation in skeletal muscles, induced by a long-term increase in blood flow which elevates capillary shear stress, is associated with capillary expression of vascular endothelial growth factor (VEGF). METHODS: Adult rats received prazosin in drinking water ( approximately 2 mg per day) or had extensor digitorum longus (EDL) muscles stimulated by implanted electrodes for up to 14 days. At intervals, serial frozen sections of EDL were stained for alkaline phosphatase to identify capillaries, proliferating cell nuclear antigen (PCNA), and VEGF-A protein. Shear stress was estimated from capillary red blood cell velocities and diameters, measured by direct observation of epi-illuminated EDL. RESULTS: Chronic stimulation and prazosin treatment both increased capillary: fiber ratio by approximately 40% after 14 days. In stimulated muscles, the percentage of capillaries positively stained for VEGF increased within 3 to 4 days, while the density of PCNA-positive capillaries had increased 20-fold after 2 days. With prazosin, VEGF-positive capillaries increased after 2 and 4 days, accompanied by a threefold increase in PCNA. By 14 days, PCNA labeling and VEGF were still high in stimulated muscles, but no longer different from controls with prazosin. After 3 to 4 days of treatment, capillary shear stress in resting muscle was 57% higher than in controls as a result of stimulation, but 4 times higher with prazosin. CONCLUSIONS: Higher capillary shear stress with prazosin than with stimulation may upregulate VEGF expression in the early stages of treatment. Greater proliferation of capillaries preceding a higher proportion of VEGF-positive capillaries in stimulated muscles, in the presence of a modest increase in shear stress, suggests that angiogenesis was initiated by other factors in addition to shear stress.

Alkaline Phosphatase↗

PubMed2001

Differential effects of cold exposure on muscle fibre composition and capillary supply in hibernator and non-hibernator rodents.

Changes in the composition of fibre types and the capillary supply of skeletal muscle (tibialis anterior) were quantified in rats and hamsters subjected to 8-10 weeks of cold exposure and reduced photoperiod (10 degrees C, 1 h light-23 h dark). Muscle mass decreased in both species (by 12% and 17%, respectively). Following acclimation to cold there were no specific changes in fibre cross-sectional area (FCSA) in rats, whereas in hamsters there was a substantial atrophy of Type II, but not Type I fibres. In rat muscle there was little difference between the two groups in average capillary to fibre ratio (C:F) (1.76 +/- 0.15, normothermia, N; 1.69 +/- 0.05, hypothermia, H) and average capillary density (CD) (188 +/- 14 mm(-2), N; 201 +/- 12 mm(-2,) H). Similarly, the average C:F was unaltered in hamsters (2.75 +/- 0.11, N; 2.72 +/- 0.15, H), although the 30 % smaller fibre size observed with hypothermia resulted in a corresponding increase in average CD, to 1539 +/- 80 mm(-2) (P < 0.01). However, there was a coordinated regional adaptation to cold exposure in hamsters resulting in capillary rarefaction in the glycolytic cortex and angiogenesis in the oxidative core. Following acclimation of rats to cold there was a reduction in the supply area of individual vessels (capillary domain), particularly in the cortex (9310, N; 8938 microm2, H; P < 0.05). In contrast, hypothermic hamsters showed only a small decrease in mean domain area in the cortex (948 microm2, N; 846 microm2, H; n.s.) but a marked reduction in the core (871 microm2, N; 604 microm2, H; P < 0.01). Rats showed little or no change in local capillary supply (LCFR) to fast fibres on acclimation to cold, while in hamsters the LCFR of Type IIb fibres showed a decrease in the cortex (2.7, N; 2.3, H) and an increase in the core (3.0, N; 3.3, H) during acclimation to cold. These data suggest that during a simulated onset of winter rats maintain FCSA and capillary supply as part of an avoidance strategy, whereas hamsters increase muscle capillarity in part as a consequence of disuse atrophy.

Acclimatization↗

PubMed2001

Relationship between capillary angiogenesis, fiber type, and fiber size in chronic systemic hypoxia.

Whether chronic hypoxia causes angiogenesis in skeletal muscle is controversial. Male Wistar rats, 5--6 wk of age, were kept at constant 12% O(2) for 3 wk, and frozen sections of their postural soleus (SOL), phasic extensor digitorum longus (EDL), and tibialis anterior (TA) muscles were compared with those of normoxic controls. Capillary supply increased in SOL muscles [capillary-to-fiber ratio (C/F) = 2.55 +/- 0.09 hypoxia vs. 2.17 +/- 0.06 normoxia; capillary density (CD) = 942 +/- 14 hypoxia vs. 832 +/- 20 mm(-2) normoxia, P < 0.01] but not in EDL muscles (C/F = 1.44 +/- 0.04 hypoxia vs. 1.42 +/- 0.04 normoxia; CD = 876 +/- 52 hypoxia vs. 896 +/- 24 mm(-2) normoxia). The predominantly glycolytic cortex of TA muscles showed higher C/F after hypoxia (1.79 +/- 0.09 vs. 1.53 +/- 0.05 normoxia, P < 0.05), whereas the mainly oxidative TA core with smaller fibers showed no change in capillarity. The region of the SOL muscle with large-sized (mean fiber area 2,843 +/- 128 microm(2)) oxidative fibers (90% type I) had a higher C/F (by 30%) and CD (by 25%), whereas there was no angiogenesis in the region with sparse (76%) and smaller-sized (2,200 +/- 85 microm(2)) type I fibers. Thus systemic hypoxia differentially induces angiogenesis between and within hindlimb skeletal muscles, with fiber size contributing either directly (via a metabolic stimulus) or indirectly (via a mechanical stimulus) to the process.

Animals↗

PubMed2001

Control of vascular tone in notothenioid fishes is determined by phylogeny, not environmental temperature.

We examined potential vasomotor control mechanisms in an Antarctic fish (Trematomus bernacchii; usual core temperature approximately -1 degrees C), comparing sensitivity to agonists by means of the cumulative dose response and potency with reference to depolarization by 50 mM KCl. In efferent branchial arteries, norepinephrine (NE) produced approximately 20% of the maximal KCl tension and ~40% in the presence of 10(-3)M sotalol, suggesting a modest contribution of alpha- and beta-adrenergic tonus [half-maximal response (pEC(50)) = 6.29 +/- 0.37 M]. Carbachol (CBC) and serotonin (5-HT) had different sensitivities (pEC(50) = 4.50 +/- 0.40 and 6.82 +/- 0.08 M, respectively) but similar potencies (21.6 +/- 11.1 and 31.1 +/- 5.3% of KCl). A related species from warmer waters around New Zealand, Paranotothenia angustata, had similar vascular reactivity for NE (pEC(50) = 5.48 +/- 0.31 M), CBC (pEC(50) = 4.94 +/- 0.22 M), and methysergide-sensitive vasoconstriction with 5-HT (pEC(50) = 6.22 +/- 0.40 M). Agonist potencies were 9, 65, and 45% that of KCl, respectively. Bovichtus variegatus, a member of the phylogenetic sister group to the notothenioids, also gave broadly similar responses. In contrast, Dissostichus mawsoni, a pelagic Antarctic notothenioid, showed a dominance of vasodilatation over vasoconstriction, with sensitive isoprenaline (pEC(50) = 6.66 +/- 0.05 M) but weak serotonergic (5.2 +/- 1.5% KCl) responses. The unusual dominance of serotonergic control appears to be primarily a consequence of evolutionary lineage rather than low environmental temperature, but the pattern may be modified according to functional demand.

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

Matrix metalloproteinase activity is required for activity-induced angiogenesis in rat skeletal muscle.

Proteolysis of the capillary basement membrane is a hallmark of inflammation-mediated angiogenesis, but it is undetermined whether proteolysis plays a critical role in the process of activity-induced angiogenesis. Matrix metalloproteinases (MMPs) constitute the major class of proteases responsible for degradation of basement membrane proteins. We observed significant elevations of mRNA and protein levels of both MMP-2 and membrane type 1 (MT1)-MMP (2.9 +/- 0.7- and 1.5 +/- 0.1-fold above control, respectively) after 3 days of chronic electrical stimulation of rat skeletal muscle. Inhibition of MMP activity via the inhibitor GM-6001 prevented the growth of new capillaries as assessed by the capillary-to-fiber ratio (1.34 +/- 0.08 in GM-6001-treated muscles compared with 1.69 +/- 0.03 in control 7-day-stimulated muscles). This inhibition correlated with a significant reduction in the number of capillaries with observable breaks in the basement membrane, as assessed by electron microscopy (0.27 +/- 0.27% in GM-6001-treated muscles compared with 3.72 +/- 0.65% in control stimulated muscles). Proliferation of capillary-associated cells was significantly elevated by 2 days and remained elevated throughout 14 days of stimulation. Capillary-associated cell proliferation during muscle stimulation was not affected by MMP inhibition (80.3 +/- 9.3 nuclei in control and 63.5 +/- 8.5 nuclei in GM-6001-treated animals). We conclude that MMP proteolysis of capillary basement membrane proteins is a critical component of physiological angiogenesis, and we postulate that capillary-associated proliferation precedes and occurs independently of endothelial cell sprout formation.

Animals↗

PubMed2000

Thermal compensation of peripheral oxygen transport in skeletal muscle of seasonally acclimatized trout.

Seasonal changes in ultrastructure of locomotory muscle were quantified after acclimatization to natural temperature and photoperiod. Only modest changes were seen in the volume density (V(v)) of mitochondria in slow fibers ranging from 0.21 +/- 0.01 (summer) to 0.24 +/- 0.01 (winter), despite an increase in fiber size from 945 +/- 19 to 1,594 +/- 46 microm(2), respectively, resulting in a significantly greater total mitochondrial volume at low temperatures. In contrast, intracellular lipid stores showed a marked change with season, from a maximum V(v) of lipid droplets of 0.16 +/- 0.01 in winter, progressively declining through spring and summer to a minimum of 0.07 +/- 0.01 in autumn. For both organelles, the surface density reflected changes in V(v), indicating little modification of structure. Seasonal effects may dominate those of environmental temperature on mitochondrial separation, which in winter and spring fish at 4(o)C averaged 0.64 +/- 0.06 and 1.20 +/- 0.07 microm, respectively. The extracellular transport of oxygen also varies with season, the peak capillary density in autumn (2,851 +/- 88 mm(-2)) resulting in a minimum tissue supply (domain) area of 529 +/- 9 microm(2) per capillary. As a consequence, the predicted intracellular PO(2) ( approximately 2.5 kPa) is similar throughout the year.

Acclimatization↗

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↗