139 research outputs found
The effects of aging on capillary hemodynamics in contracting rat spinotrapezius muscle
No full textMaster of ScienceDepartment of KinesiologyTimothy I. MuschAdvancing age alters the structural and functional determinants of convective and diffusive muscle oxygen (O[subscript]2) flux. However, capillary red blood cell (RBC) hemodynamics have not been investigated during contractions in muscles of old animals. PURPOSE: To test the hypothesis that aging induces significant alterations in capillary hemodynamics during electrically-induced contractions in the spinotrapezius muscle of old Fischer 344 x Brown Norway rats when compared to younger counterparts. METHODS: The spinotrapezius muscle was observed via intravital microscopy in 8 old (O: 26-30 months) and 5 young (Y: 6-8 months) animals. Wire electrodes elicited 1 Hz (6-8 volts) contractions for 3 minutes. RBC flux (FRBC), velocity (VRBC), capillary hematocrit (HCAP), and total microvascular O[subscript]2 delivery (QO[subscript]2m) were measured both at rest and during the steady-state of muscle contractions. RESULTS: At rest F[subscript]RBC and V[subscript]RBC were elevated in O compared to Y rats, while there was no difference in HCAP or QO[subscript]2m between groups. During the contracting steady-state, [Delta]F[subscript]RBC (Y: 28.8 [plus or minus] 7.7, O: -2.9 [plus or minus] 1.4 cells/s), [Delta]V[subscript]RBC (Y: 253 [plus or minus] 68, O: -4 [plus or minus] 15 [Mu]m/s), [Delta]H[subscript]CAP (Y: 0.02 [plus or minus] 0.02, O: -0.03 [plus or minus] 0.01 cells/[Mu]m), and [Delta]QO[subscript]2m (Y: 892 [plus or minus] 255, O: -24 [plus or minus] 30 cells/s/mm) cells/s/mm were all lower (P < 0.05) in O compared to Y rats. CONCLUSION: These results indicate that despite maintained total convective and diffusive O[subscript]2 transport at rest, advancing age results in significant alterations in capillary hemodynamics during electrically-induced contractions. These alterations likely contribute to the mechanisms responsible for the reduced exercise capacity commonly found in elderly populations
The female high school athlete and achievement : an analysis of race differences
No full textTypescript (photocopy).The major goal of this research is to examine the effects of high school sport participation on career and academic achievements for black and white females. Status attainment research provides the theoretical basis for this analysis. Data from two studies are used. The first, "The Southern Youth Study," was a longitudinal study conducted in 1966, 1968, 1972 and 1979. The second study, "High School and Beyond" involved a sample of students who were high school seniors in 1980. Achievement was measured in terms of grades, educational aspirations, adult educational attainment, adult occupational attainment, and adult monthly earnings. Causal models hypothesizing the relationship between sport participation and achievement were tested using path analysis; and, generally, the results showed that high school sport participation had positive effects on achievement-related variables for white females, but it had negative or neutral effects for black females. It was concluded that for white females high school sport participation helps to create an educational and social environment conducive to achievement
Skeletal muscle capillary function: contemporary observations and novel hypotheses
No full textThe capillary bed constitutes a vast surface that facilitates exchange of O2, substrates and metabolites between blood and organs. In contracting skeletal muscle, capillary blood flow and O2 diffusing capacity, as well as O2 flux, may increase two orders of magnitude above resting values. Chronic diseases, such as heart failure and diabetes, and also sepsis impair these processes, leading to compromised energetic, metabolic and, ultimately, contractile function. Among researchers seeking to understand blood–myocyte exchange in health and the basis for dysfunction in disease, there is a fundamental disconnect between microcirculation specialists and many physiologists and physiologist clinicians. While the former observe capillaries and capillary function directly (muscle intravital microscopy), the latter generally use indirect methodologies (e.g. post-mortem tissue analysis, 1-methyl xanthine, contrast-enhanced ultrasound, permeability–surface area product) and interpret their findings based upon August Krogh's observations made nearly a century ago. ‘Kroghian’ theory holds that only a small fraction of capillaries support red blood cell (RBC) flux in resting muscle, leaving the vast majority to be ‘recruited’ (i.e. to initiate RBC flux) during contractions, which would constitute the basis for increasing surface area for capillary exchange and reducing capillary–mitochondrial diffusion distances. Experimental techniques each have their strengths and weaknesses, and often the correct or complete answer to a problem emerges from integration across multiple technologies. Today, Krogh's entrenched ‘capillary recruitment’ hypothesis is challenged by direct observations of capillaries in contracting muscle, which is something that he and his colleagues could not do. Moreover, in the peer-reviewed scientific literature, application of a range of contemporary physiological technologies, including intravital microscopy of contracting muscle, magnetic resonance, near-infrared spectroscopy and phosphorescence quenching, combined with elegant in situ and in vivo models, suggest that the role of the capillary bed, at least in contracting muscle, is subserved without the necessity for de novo capillary recruitment of previously non-flowing capillaries. When viewed within the context of the capillary recruitment hypothesis, this evidence casts serious doubt on the interpretation of those data that are based upon Kroghian theory and indirect methodologies. Thus, today a wealth of evidence calls for a radical revision of blood–muscle exchange theory to one in which most capillaries support RBC flux at rest and, during contractions, capillary surface area is ‘recruited’ along the length of previously flowing capillaries. This occurs, in part, by elevating capillary haematocrit and extending the length of the capillary available for blood–myocyte exchange (i.e. longitudinal recruitment). Our understanding of blood–myocyte O2 and substrate/metabolite exchange in health and the mechanistic basis for dysfunction in disease demands no less
Liberal legitimacy : a study of the normative foundations of liberalism
No full textThis thesis is a critique of the prominent strand of contemporary liberal political
theory which maintains that liberal political authority must, in some sense, rest
on the free consent of those subjected to it, and that such a consensus is
achieved if a polity’s basic structure can be publicly justified to its citizenry, or to
a relevant subset of it. Call that the liberal legitimacy view. I argue that the
liberal legitimacy view cannot provide viable normative foundations for political
authority, for the hypothetical consensus it envisages cannot be achieved and
sustained without either arbitrarily excluding conspicuous sectors of the citizenry
or commanding a consent that is less than free. That is because the liberal
legitimacy view’s structure is one that requires a form of consent that carries
free-standing normative force (i.e. normative force generated by voluntariness),
yet the particular form of hypothetical consent through public justification
envisaged by the view does not possess such force, because of its built-in bias in
favour of liberalism. I also argue that the liberal legitimacy view is the most
recent instantiation of one of two main strands of liberal theory, namely the
nowadays dominant contract-based liberalism, which seeks to ground liberal
political authority in a hypothetical agreement between the citizens. My case
against the liberal legitimacy view, then, contributes to the revitalisation of the
other main approach to the normative foundations of liberalism, namely the
substantivist one, which legitimates liberal political authority through an appeal
to the substantive values and virtues safeguarded and promoted by liberal
polities
The NO donor sodium nitroprusside: evaluation of skeletal muscle vascular and metabolic dysfunction
No full textThe nitric oxide (NO) donor sodium nitroprusside (SNP) may promote cyanide-induced toxicity and systemic and/or local responses approaching maximal vasodilation. The hypotheses were tested that SNP superfusion of the rat spinotrapezius muscle exerts 1) residual impairments in resting and contracting blood flow, oxygen utilization (VO[subscript 2]) and microvascular O[subscript 2] pressure (PO[subscript 2mv]); and 2) marked hypotension and elevation in resting PO[subscript 2mv]. Two superfusion protocols were performed: 1) Krebs-Henseleit (control 1), SNP (300 μM; a dose used commonly in superfusion studies) and Krebs-Henseleit (control 2), in this order; 2) 300 and 1200 μM SNP in random order. Spinotrapezius muscle blood flow (radiolabeled microspheres), VO[subscript 2] (Fick calculation) and PO[subscript 2mv] (phosphorescence quenching) were determined at rest and during electrically-induced (1 Hz) contractions. There were no differences in spinotrapezius blood flow, VO[subscript 2] or PO[subscript 2mv] at rest and during contractions pre- and post-SNP condition (control 1 and control 2; p>0.05 for all). With regard to dosing, SNP produced a graded elevation in resting PO[subscript 2mv] (p<0.05) with a reduction in mean arterial pressure only at the higher concentration (p<0.05). Contrary to our hypothesis, skeletal muscle superfusion with the NO donor SNP (300 μM) improved microvascular oxygenation during the transition from rest to contractions (PO[subscript 2mv] kinetics) without precipitating residual impairment of muscle hemodynamic or metabolic control
or compromising systemic hemodynamics. These data suggest that SNP superfusion (300 μM) constitutes a valid and important tool for assessing the functional roles of NO in resting and contracting skeletal muscle function without incurring residual alterations consistent with cyanide accumulation and poisoning
The effects of dietary fish oil on exercising skeletal muscle vascular and metabolic control in chronic heart failure rats
No full textThe ATP-sensitive K+ (KATP) channel is a class of inward rectifier K+ channels that can link cellular metabolic status to vasomotor tone across the metabolic transients seen with exercise. This investigation tested the hypothesis that if KATP channels are crucial to exercise hyperaemia then blockade via glibenclamide (GLI) would lower hindlimb skeletal muscle blood flow (BF) and vascular conductance (VC) during treadmill exercise. In 14 adult male Sprague Dawley rats mean arterial pressure (MAP), blood [lactate], and hindlimb muscle BF (radiolabelled microspheres) were determined at rest (n = 6) or during exercise (n = 8; 20 m min⁻¹, 5% incline) under control (CON) and GLI conditions (5 mg kg⁻¹, i.a). At rest and during exercise, MAP was higher (Rest, CON: 130 ± 6, GLI: 152 ± 8; Exercise, CON: 140 ± 4, GLI: 147 ± 4 mmHg, P < 0.05) and heart rate (HR) was lower (Rest, CON: 440 ± 16, GLI: 410 ± 18; Exercise, CON: 560 ± 4, GLI: 540 ± 10 beats min⁻¹, P < 0.05) with GLI. Hindlimb muscle BF (CON: 144 ± 10, GLI: 120 ± 9 ml min⁻¹ (100 g)⁻¹, P < 0.05) and VC were lower with GLI during exercise but not at rest. Specifically, GLI decreased BF in 12, and VC in 16, of the 28 individual hindlimb muscles and muscle parts sampled during exercise with a greater fractional reduction present in muscles comprised predominantly of type I and type IIa fibres (P < 0.05). Additionally, blood [lactate] (CON: 2.0 ± 0.3; GLI: 4.1 ± 0.9 mmol L⁻¹, P < 0.05) was higher during exercise with GLI. That KATP channel blockade reduces hindlimb muscle BF during exercise in rats supports the obligatory contribution of KATP channels in large muscle mass exercise-induced hyperaemia
Dose dependent effects of nitrate supplementation on cardiovascular control and microvascular oxygenation dynamics in healthy rats
No full textHigh dose nitrate (NO3−) supplementation via beetroot juice (BR, 1 mmol/kg/day) lowers mean arterial blood pressure (MAP) and improves skeletal muscle blood flow and O2 delivery/utilization matching thereby raising microvascular O2 pressure (PO2mv). We tested the hypothesis that a low dose of NO3− supplementation, consistent with a diet containing NO3− rich vegetables (BRLD, 0.3 mmol/kg/day), would be sufficient to cause these effects. Male Sprague–Dawley rats were administered a low dose of NO3− (0.3 mmol/kg/day; n = 12), a high dose (1 mmol/kg/day; BRHD, n = 6) or tap water (control, n = 10) for 5 days. MAP, heart rate (HR), blood flow (radiolabeled microspheres) and vascular conductance (VC) were measured during submaximal treadmill exercise (20 m/min, 5% grade, equivalent to ∼60% of maximal O2 uptake). Subsequently, PO2mv (phosphorescence quenching) was measured at rest and during 180 s of electrically-induced twitch contractions (1 Hz, ∼6 V) of the surgically-exposed spinotrapezius muscle. BRLD and BRHD lowered resting (control: 139 ± 4, BRLD: 124 ± 5, BRHD: 128 ± 9 mmHg, P 0.05), each of which increased significantly for the BRHD condition (all P mean response time, MRT; control: 16.6 ± 2.1, BRHD: 23.3 ± 4.7 s) following the onset of contractions compared to control, in the BRLD group this effect did not reach statistical significance (BRLD: 20.9 ± 1.9 s, P = 0.14). These data demonstrate that while low dose NO3− supplementation lowers MAP during exercise it does so in the absence of augmented muscle blood flow, VC and PO2mv; all of which are elevated at a higher dose. Thus, in healthy animals, a high dose of NO3− supplementation seems necessary to elicit significant changes in exercising skeletal muscle O2 delivery/utilization
Impact of dietary nitrate supplementation via beetroot juice on exercising muscle vascular control in rats
No full textDietary nitrate (NO[subscript 3]ˉ) supplementation, via its reduction to nitrite (NO[subscript 2]ˉ) and subsequent conversion to nitric oxide (NO) and other reactive nitrogen intermediates, reduces blood pressure and the O[subscript 2] cost of submaximal exercise in humans. Despite these observations, the effects of dietary NO[subscript 3]ˉ supplementation on skeletal muscle vascular control during locomotory exercise remain unknown. We tested the hypotheses that dietary NO[subscript 3]ˉ supplementation via beetroot juice (BR) would reduce mean arterial pressure (MAP) and increase hindlimb muscle blood flow in the exercising rat. Male Sprague–Dawley rats (3–6 months) were administered either NO[subscript 3]ˉ (via beetroot juice; 1 mmol ∙ kgˉ¹ ∙ dayˉ¹, BR n=8) or untreated (control, n = 11) tap water for 5 days. MAP and hindlimb skeletal muscle blood flow and vascular conductance (radiolabelled microsphere infusions) were measured during submaximal treadmill running (20 m ∙ minˉ¹, 5% grade). BR resulted in significantly lower exercising MAP (control: 137 ± 3, BR: 127 ± 4 mmHg, P < 0.05) and blood [lactate] (control: 2.6 ± 0.3, BR: 1.9 ± 0.2 mm, P < 0.05) compared to control. Total exercising hindlimb skeletal muscle blood flow (control: 108 ± 8, BR: 150 ± 11 ml ∙ minˉ¹ ∙ 100 gˉ¹, P<0.05) and vascular conductance (control: 0.78 ± 0.05, BR: 1.16 ± 0.10 ml ∙ minˉ¹ ∙ 100 gˉ¹ ∙ mmHgˉ¹, P<0.05) were greater in rats that received BR compared to control. The relative differences in blood flow and vascular conductance for the 28 individual hindlimb muscles and muscle parts correlated positively with their percentage type IIb + d/x muscle fibres (blood flow: r = 0.74, vascular conductance: r = 0.71, P < 0.01 for both). These data support the hypothesis that NO[subscript 3]ˉ supplementation improves vascular control and elevates skeletal muscle O[subscript 2] delivery during exercise predominantly in fast-twitch type II muscles, and provide a potential mechanism by which NO[subscript 3]ˉ supplementation improves metabolic control
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