Muscle Contraction Duration and Fibre Recruitment Influence Blood Flow and VO2 Independent of Contractile Work during Steady-State Exercise in Humans

We tested the hypothesis that, among conditions of matched contractile work, shorter contraction durations and greater muscle fibre recruitment result in augmented skeletal muscle blood flow and oxygen consumption (O2) during steady-state exercise in humans. To do so, we measured forearm blood flow (FBF; Doppler ultrasound) during 4 minutes of rhythmic handgrip exercise in 24 healthy young adults and calculated forearm O2 via blood samples obtained from a catheter placed in retrograde fashion into a deep vein draining the forearm muscle. In Protocol 1 (n = 11), subjects performed rhythmic isometric handgrip exercise at mild and moderate intensities under conditions in which tension time index (TTI; isometric analog of work) was held constant but contraction duration was manipulated. In this protocol, shorter contraction durations led to greater FBF (184 ± 25 vs. 164 ± 25 ml·min-1) and O2 (23 ± 3 vs. 17 ± 2 ml·min-1; both PPper se during steady-state exercise in humans

Reactive Hyperemia Occurs Via Activation of Inwardly Rectifying Potassium Channels and Na+/K+-ATPase in Humans

Rationale: Reactive hyperemia (RH) in the forearm circulation is an important marker of cardiovascular health, yet the underlying vasodilator signaling pathways are controversial and thus remain unclear. Objective: We hypothesized that RH occurs via activation of inwardly rectifying potassium (KIR) channels and Na+/K+-ATPase and is largely independent of the combined production of the endothelial autocoids nitric oxide (NO) and prostaglandins in young healthy humans. Methods and Results: In 24 (23±1 years) subjects, we performed RH trials by measuring forearm blood flow (FBF; venous occlusion plethysmography) after 5 minutes of arterial occlusion. In protocol 1, we studied 2 groups of 8 subjects and assessed RH in the following conditions. For group 1, we studied control (saline), KIR channel inhibition (BaCl2), combined inhibition of KIR channels and Na+/K+-ATPase (BaCl2 and ouabain, respectively), and combined inhibition of KIR channels, Na+/K+-ATPase, NO, and prostaglandins (BaCl2, ouabain, L-NMMA [NG-monomethyl-L-arginine] and ketorolac, respectively). Group 2 received ouabain rather than BaCl2 in the second trial. In protocol 2 (n=8), the following 3 RH trials were performed: control; L-NMMA plus ketorolac; and L-NMMA plus ketorolac plus BaCl2 plus ouabain. All infusions were intra-arterial (brachial). Compared with control, BaCl2 significantly reduced peak FBF (−50±6%; P2 (−61±3%) and ouabain (−44±12%) alone, and this effect was enhanced when combined (−87±4%), nearly abolishing RH. L-NMMA plus ketorolac did not impact total RH FBF before or after administration of BaCl2 plus ouabain. Conclusions: Activation of KIR channels is the primary determinant of peak RH, whereas activation of both KIR channels and Na+/K+-ATPase explains nearly all of the total (AUC) RH in humans

Impaired Peripheral Vasodilation during Graded Systemic Hypoxia in Healthy Older Adults: Role of the Sympathoadrenal System

Systemic hypoxia is a physiological and pathophysiological stress that activates the sympathoadrenal system and, in young adults, leads to peripheral vasodilation. We tested the hypothesis that peripheral vasodilation to graded systemic hypoxia is impaired in older healthy adults and that this age-associated impairment is due to attenuated β-adrenergic mediated vasodilation and elevated α-adrenergic vasoconstriction. Forearm blood flow was measured (Doppler ultrasound) and vascular conductance (FVC) was calculated in 12 young (24±1 yrs) and 10 older (63±2 yrs) adults to determine the local dilatory responses to graded hypoxia (90, 85, and 80% O2 saturations) in control conditions, following local intra-arterial blockade of β-receptors (propranolol), and combined blockade of α+β receptors (phentolamine + propranolol). Under control conditions, older adults exhibited impaired vasodilation to hypoxia compared with young at all levels of hypoxia (peak ΔFVC at 80% SpO2 = 4±6 vs. 35±8%; P\u3c0.01). During β-blockade, older adults actively constricted at 85 and 80% SpO2 (peak ΔFVC at 80% SpO2= -13±6%; P\u3c0.05 vs. control) whereas the response in the young was not significantly impacted (peak ΔFVC = 28±8%). Combined α+β blockade increased the dilatory response to hypoxia in young adults, however older adults failed to significantly vasodilate (peak ΔFVC at 80% SpO2= 12±11% vs. 58±11%; P\u3c0.05). Our findings indicate that peripheral vasodilation to graded systemic hypoxia is significantly impaired in older adults which cannot be fully explained by altered sympathoadrenal control of vascular tone. Thus, the impairment in hypoxic vasodilation is likely due to attenuated local vasodilatory and/or augmented vasoconstrictor signaling with age

Sources of Intravascular ATP During Exercise in Humans: Critical Role for Skeletal Muscle Perfusion

Exercise hyperemia is regulated by several factors and one factor known to increase with exercise that evokes powerful vasomotor action is extracellular ATP. The origination of ATP detectable in plasma from exercising muscle of humans is, however, a matter of debate and ATP has been suggested to arise from sympathetic nerves, blood sources (e.g. erythrocytes), endothelial cells, and skeletal myocytes, among others. Therefore, we tested the hypothesis that acute augmentation of sympathetic nervous system activity (SNA) results in elevated plasma ATP draining skeletal muscle, and that SNA superimposition during exercise further increases ATP vs exercise alone. We show that increased SNA via −40mmHg lower body negative pressure (LBNP) at rest does not increase plasma ATP (51±8 vs 58±7 nmol/L with LBNP), nor does it increase [ATP] above levels observed during rhythmic handgrip exercise (79±11 exercise alone vs 71±8 nmol/L with LBNP). Secondly, we tested the hypothesis that active perfusion of skeletal muscle is essential to observe increased plasma ATP during exercise. We identify that complete obstruction of blood flow to contracting muscle abolishes exercise-mediated increases in plasma ATP (90±19 to 49±12 nmol/L), and further, that cessation of blood flow prior to exercise completely inhibits the typical rise in ATP (3 vs 61%; obstructed vs intact perfusion). The lack of ATP change during occlusion occurred in the face of continued muscle work and elevated SNA, indicating the rise of intravascular ATP is not resultant from these extravascular sources. Our collective observations indicate that the elevation in extracellular ATP observed in blood during exercise is unlikely to originate from sympathetic nerves or the contacting muscle itself, but rather is dependent on intact skeletal muscle perfusion. We conclude that an intravascular source for ATP is essential and points toward an important role for blood sources (e.g. red blood cells) in augmenting and maintaining elevated plasma ATP during exercise

Einfluss der Insektenherbivorie auf den Kreislauf fester und gelöster organischer Substanzen in einem Grasslandökosystem - eine Mesokosmenstudie

Insektenmassenvermehrungen können durch die Reduktion von oberirdischer Biomasse (z.B. Blattverlust) und Koteintrag Einfluss auf den Kreislauf der organischen Substanz in Ökosystemen nehmen und dadurch zeitlich und räumlich begrenzte massive Veränderungen biogeochemischer Reaktionsraten hervorrufen. Um die Auswirkungen auf den C- und N-Kreislauf in Grasländern im System Herbivore-Pflanze-Boden zu quantifizieren, wurde ein Mesokosmenexperiment (D: 50 cm, H: 100 cm) mit Knäuelgras (Dactylis glomerata) und Heuschrecken (Chorthippus dorsatus) durchgeführt. Mit Hilfe von C-13-O2-Gas und N-15 markiertem Kot (δN-15: 58‰) wurde der C- und N-Pfad in den Kompartimenten Blatt, Wurzel, Grashüpfer, Kot, Boden und in der Eintrags- und Bodenlösung verfolgt. Es wurden folgende vier Varianten durchgeführt (n=3): Kontrolle; C-13-O2; C-13-O2+20_Grashüpfer; C-13-O2+20_Grashüpfer+N-15-markierter Kot (+9.2 µg N*cm-2). Innerhalb einer 5-Tage-Inkubation wurden die Kosmen bewässert (13 mm/5d). Nach fünf Tagen wurden die Bodenlösungen und die Kaltwasser- sowie mikrobielle Biomasse-Extrakte (CFE) (0-4, 4-12 cm) auf gelösten OC, OδC-13 und N untersucht. Ebenfalls wurden TOC, δC-13, TN sowie δN-15 Werte aller Kompartimente bestimmt. Nach fünf Tagen waren sowohl die Grashüpfer, der Kot als auch die Eintragslösung des Kotes signifikant mit C-13 angereichert. C-13 wurde stärker in Wurzeln als in Blätter eingebaut (anhand δC-13-Werten). Erhöhte DOC-13 Werte im Boden weisen auf einen schnellen Blatt-C-Kreislauf über Grashüpfer, Kot bis in die Bodenlösung, die Bodenorganismen und die Graswurzeln hin. Dies wird ebenfalls durch den zugegebenen N-15 Kot deutlich, welcher um 91% seines Gesamt-N-Gehaltes reduziert wurde. Es scheint eine schnelle N-Freisetzung durch Auswaschung und Wurzelaufnahme (-0.82±0.28‰ vs -1.54±0.12‰) stattgefunden zu haben. N-15 war im frisch produzierten Kot (0.62±0.4‰ vs -0.14 ±0.27‰) aber nicht in den Blättern angereichert. Die Herbivorie hatte keinen Einfluss auf die N-Menge in der Bodenlösung und in den Extrakten, was eine schnelle Pflanzenaufnahme des freigewordenen N vermuten lässt. Die geringe N-Konzentration des Mineralbodens (0.14%) und der Bodenlösungen (1-2.3 mg*L-1) weisen im Allgemeinen auf eine geringe Pflanzen-N-Verfügbarkeit hin. Wir schließen daraus, dass innerhalb des kurzen zeitlichen Umfanges (5d) N-limitierte Weidesysteme robust auf starken Insektenbefall reagieren und nicht zu signifikanten, ökosystemaren N-Auswaschungsverlusten neigen

The Case for Coordinating Efforts to Establish Program Guidelines and Strengthen Physiology Undergraduate Degree Programs

Undergraduate degree programs named “Physiology” have existed for over 50 yr. The number of programs and enrolled students have been growing since ~2005 (5, 9). There are many thousands of students currently enrolled in physiology pro- grams across the United States and indeed across the world. Despite the long history and current popularity of the physiol- ogy major, there is no coordinated plan articulated for the design, administration, or assessment of degree programs in physiology at the undergraduate level. Although several professional societies have invested in under- graduate physiology education in various ways, none has under- taken the task of developing programmatic guidelines at the level of a degree program. This paper outlines the work being done by multiple stakeholders in physiology undergraduate education in the hopes of building a collaboration among interested parties. A large-scale collaboration could result in establishing consensus national programmatic guidelines. Through coordinated efforts, we ensure that entities with common educational interests are working together, and we collectively strengthen our programs to help our students succeed. The goals of this paper are to: 1) draw attention to the lack of national, program-level guidelines for physiology under- graduate degree programs; 2) share ongoing efforts by stake- holders in physiology undergraduate education; 3) suggest a mechanism for coordination among stakeholders; and 4) dis- cuss challenges and considerations for development of pro- grammatic guidelines for physiology programs

Forearm vasodilator responses to environmental stress and reactive hyperaemia are impaired in young South Asian men

© 2018, The Author(s). Purpose: Prevalence of cardiovascular disease (CVD) is greater in South Asians (SAs) than White Europeans (WEs). Endothelial dysfunction and blunted forearm vasodilatation to environmental stressors have been implicated in CVD. We investigated whether these features are present in young SA men. Methods: In 15 SA and 16 WE men (19–23 years), we compared changes in forearm blood flow, arterial blood pressure (ABP), forearm vascular conductance (FVC), heart rate, and electrodermal resistance (EDR; sweating) following release of arterial occlusion (reactive hyperaemia endothelium-dependent) and 5 single sounds at 5–10 min intervals (stressors). Results: All were normotensive. Peak reactive hyperaemia was smaller in SAs than WEs (FVC increase: 0.36 ± 0.038 vs 0.44 ± 0.038 units; P < 0.05). Furthermore, in WEs, mean FVC increased at 5, 15, and 20 s of each sound (vasodilatation), but increased at 5 s only in SAs, decreasing by 20 s (vasoconstriction). This reflected a smaller proportion of SAs showing forearm vasodilatation at 15 s (5/15 SAs vs 11/16 WEs: P < 0.01), the remainder showing vasoconstriction. Concomitantly, WEs showed greater bradycardia and EDR changes. Intra-class correlation analyses showed that all responses were highly reproducible over five sounds in both WEs and SAs. Moreover, sound-evoked changes in ABP and FVC were negatively correlated in each ethnicity (P < 0.01). However, WEs showed preponderance of forearm vasodilatation and depressor responses; SAs showed preponderance of vasoconstriction and pressor responses. Conclusions: Endothelium-dependent vasodilatation is blunted in young SA men. This could explain their impaired forearm vasodilatation and greater pressor responses to repeated environmental stressors, so predisposing SAs to hypertension and CVD