Reptile-like physiology in Early Jurassic stem-mammals

AbstractThere is uncertainty regarding the timing and fossil species in which mammalian endothermy arose, with few studies of stem-mammals on key aspects of endothermy such as basal or maximum metabolic rates, or placing them in the context of living vertebrate metabolic ranges. Synchrotron X-ray imaging of incremental tooth cementum shows two Early Jurassic stem-mammals, Morganucodon and Kuehneotherium, had lifespans (a basal metabolic rate proxy) considerably longer than comparably sized living mammals, but similar to reptiles. Morganucodon also had femoral blood flow rates (a maximum metabolic rate proxy) intermediate between living mammals and reptiles. This shows maximum metabolic rates increased evolutionarily before basal rates, and that contrary to previous suggestions of a Triassic origin, Early Jurassic stem-mammals lacked the endothermic metabolism of living mammals.One Sentence SummarySurprisingly long lifespans and low femoral blood flow suggest reptile-like physiology in key Early Jurassic stem-mammals.

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High Blood Flow Into the Femur Indicates Elevated Aerobic Capacity in Synapsids Since the Synapsida-Sauropsida Split

Frontiers in Ecology and Evolution ◽

10.3389/fevo.2021.751238 ◽

2021 ◽

Vol 9 ◽

Author(s):

Philipp L. Knaus ◽

Anneke H. van Heteren ◽

Jacqueline K. Lungmus ◽

P. Martin Sander

Keyword(s):

Blood Flow ◽

Metabolic Rate ◽

Aerobic Capacity ◽

Second Step ◽

Metabolic Rates ◽

Sectional Area ◽

Cross Sectional ◽

Femoral Length ◽

Plesiomorphic State ◽

Maximum Metabolic Rate

Varanids are the only non-avian sauropsids that are known to approach the warm-blooded mammals in stamina. Furthermore, a much higher maximum metabolic rate (MMR) gives endotherms (including birds) higher stamina than crocodiles, turtles, and non-varanid lepidosaurs. This has led researchers to hypothesize that mammalian endothermy evolved as a second step after the acquisition of elevated MMR in non-mammalian therapsids from a plesiomorphic state of low metabolic rates. In recent amniotes, MMR correlates with the index of blood flow into the femur (Qi), which is calculated from femoral length and the cross-sectional area of the nutrient foramen. Thus, Qi may serve as an indicator of MMR range in extinct animals. Using the Qi proxy and phylogenetic eigenvector maps, here we show that elevated MMRs evolved near the base of Synapsida. Non-mammalian synapsids, including caseids, edaphosaurids, sphenacodontids, dicynodonts, gorgonopsids, and non-mammalian cynodonts, show Qi values in the range of recent endotherms and varanids, suggesting that raised MMRs either evolved in synapsids shortly after the Synapsida-Sauropsida split in the Mississippian or that the low MMR of lepidosaurs and turtles is apomorphic, as has been postulated for crocodiles.

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Reptile-like physiology in Early Jurassic stem-mammals

Nature Communications ◽

10.1038/s41467-020-18898-4 ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 1

Author(s):

Elis Newham ◽

Pamela G. Gill ◽

Philippa Brewer ◽

Michael J. Benton ◽

Vincent Fernandez ◽

...

Keyword(s):

Blood Flow ◽

Tomographic Imaging ◽

Early Jurassic ◽

Metabolic Rates ◽

Metabolic Evolution ◽

Flow Rates ◽

X Ray ◽

Nutrient Foramina ◽

Physiological Evolution ◽

Maximum Metabolic Rate

Abstract Despite considerable advances in knowledge of the anatomy, ecology and evolution of early mammals, far less is known about their physiology. Evidence is contradictory concerning the timing and fossil groups in which mammalian endothermy arose. To determine the state of metabolic evolution in two of the earliest stem-mammals, the Early Jurassic Morganucodon and Kuehneotherium, we use separate proxies for basal and maximum metabolic rate. Here we report, using synchrotron X-ray tomographic imaging of incremental tooth cementum, that they had maximum lifespans considerably longer than comparably sized living mammals, but similar to those of reptiles, and so they likely had reptilian-level basal metabolic rates. Measurements of femoral nutrient foramina show Morganucodon had blood flow rates intermediate between living mammals and reptiles, suggesting maximum metabolic rates increased evolutionarily before basal metabolic rates. Stem mammals lacked the elevated endothermic metabolism of living mammals, highlighting the mosaic nature of mammalian physiological evolution.

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Human muscle length-dependent changes in blood flow

Journal of Applied Physiology ◽

10.1152/japplphysiol.01223.2011 ◽

2012 ◽

Vol 112 (4) ◽

pp. 560-565 ◽

Cited By ~ 17

Author(s):

John McDaniel ◽

Stephen J. Ives ◽

Russell S. Richardson

Keyword(s):

Blood Flow ◽

Knee Joint ◽

Joint Angle ◽

Muscle Blood Flow ◽

Muscle Length ◽

Limb Blood Flow ◽

Knee Joint Angle ◽

Femoral Blood Flow ◽

Femoral Blood ◽

Cyclic Changes

Although a multitude of factors that influence skeletal muscle blood flow have been extensively investigated, the influence of muscle length on limb blood flow has received little attention. Thus the purpose of this investigation was to determine if cyclic changes in muscle length influence resting blood flow. Nine healthy men (28 ± 4 yr of age) underwent a passive knee extension protocol during which the subjects' knee joint was passively extended and flexed through 100–180° knee joint angle at a rate of 1 cycle per 30 s. Femoral blood flow, cardiac output (CO), heart rate (HR), stroke volume (SV), and mean arterial pressure (MAP) were continuously recorded during the entire protocol. These measurements revealed that slow passive changes in knee joint angle did not have a significant influence on HR, SV, MAP, or CO; however, net femoral blood flow demonstrated a curvilinear increase with knee joint angle ( r2 = 0.98) such that blood flow increased by ∼90% (125 ml/min) across the 80° range of motion. This net change in blood flow was due to a constant antegrade blood flow across knee joint angle and negative relationship between retrograde blood flow and knee joint angle ( r2 = 0.98). Thus, despite the absence of central hemodynamic changes and local metabolic factors, blood flow to the leg was altered by changes in muscle length. Therefore, when designing research protocols, researchers need to be cognizant of the fact that joint angle, and ultimately muscle length, influence limb blood flow.

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Effects of bone cement filling in rabbit proximal femoral medullary cavity on distal femoral blood flow and metabolism

Journal of International Medical Research ◽

10.1177/0300060518802717 ◽

2018 ◽

Vol 46 (12) ◽

pp. 5237-5244

Author(s):

Li-Cheng Xi ◽

Hong-Yu Li ◽

Ming Zhang ◽

Si-Cheng Huang

Keyword(s):

Blood Flow ◽

Bone Cement ◽

Rabbit Model ◽

Experimental System ◽

Medullary Cavity ◽

Marrow Cavity ◽

Femoral Blood Flow ◽

Femoral Blood ◽

The Right ◽

Time Point

Objective A rabbit model was used to evaluate the effects of bone-cemented hip arthroplasty on distal femoral blood flow and metabolism relative to that of the non-cemented contralateral leg. Methods The marrow cavity of the right hind femur was filled with bone cement. At each of the following time points, rabbits were randomly selected to receive an injection of one dose of 99mTc-methylene diphosphonate and then immediately scanned using a gamma camera: immediately postoperatively and at 4 and 8 weeks postoperatively. A BL-410 model biofunction experimental system was used to analyze the acquired images and determine the radioactive counts of each hind leg. Results The X-ray and photographic images of the right femoral bones confirmed successful filling of the marrow cavity with bone cement. The radioactive counts were significantly lower in the experimental than control legs at each time point. The ratio of the radioactive count of the experimental to control leg increased considerably at each time point, but each ratio was <1. Conclusion Blocking the proximal femoral medullary cavity with bone cement was associated with significant lowering of the blood circulation of the femur and marrow, decreasing the distal femoral blood flow and bone metabolic rate.

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Alterations in Femoral Blood Flow and Resistance During Rhythmic Exercise and Sustained Muscular Contractions in Patients with Arteriosclerosis

Physical Therapy ◽

10.1093/ptj/46.1.91b ◽

1966 ◽

Vol 46 (1) ◽

pp. 91-93

Keyword(s):

Blood Flow ◽

Femoral Blood Flow ◽

Femoral Blood ◽

Rhythmic Exercise

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Systemic and regional hemodynamic response to activation of the exercise pressor reflex in patients with peripheral artery disease

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00493.2019 ◽

2020 ◽

Vol 318 (4) ◽

pp. H916-H924 ◽

Cited By ~ 1

Author(s):

Danielle Jin-Kwang Kim ◽

Marcos Kuroki ◽

Jian Cui ◽

Zhaohui Gao ◽

J. Carter Luck ◽

...

Keyword(s):

Blood Pressure ◽

Blood Flow ◽

Peripheral Artery Disease ◽

Plantar Flexion ◽

Peripheral Artery ◽

Exercise Pressor Reflex ◽

Femoral Blood Flow ◽

Femoral Blood ◽

Pressor Reflex ◽

Artery Disease

Patients with peripheral artery disease (PAD) have an accentuated exercise pressor reflex (EPR) during exercise of the affected limb. The underlying hemodynamic changes responsible for this, and its effect on blood flow to the exercising extremity, are unclear. We tested the hypothesis that the exaggerated EPR in PAD is mediated by an increase in total peripheral resistance (TPR), which augments redistribution of blood flow to the exercising limb. Twelve patients with PAD and 12 age- and sex-matched subjects without PAD performed dynamic plantar flexion (PF) using the most symptomatic leg at progressive workloads of 2–12 kg (increased by 1 kg/min until onset of fatigue). We measured heart rate, beat-by-beat blood pressure, femoral blood flow velocity (FBV), and muscle oxygen saturation ([Formula: see text]) continuously during the exercise. Femoral blood flow (FBF) was calculated from FBV and baseline femoral artery diameter. Stroke volume (SV), cardiac output (CO), and TPR were derived from the blood pressure tracings. Mean arterial blood pressure and TPR were significantly augmented in PAD compared with control during PF. FBF increased during exercise to an equal extent in both groups. However, [Formula: see text] of the exercising limb remained significantly lower in PAD compared with control. We conclude that the exaggerated pressor response in PAD is mediated by an abnormal TPR response, which augments redistribution of blood flow to the exercising extremity, leading to an equal rise in FBF compared with controls. However, this increase in FBF is not sufficient to normalize the SmO2 response during exercise in patients with PAD. NEW & NOTEWORTHY In this study, peripheral artery disease (PAD) patients and healthy control subjects performed graded, dynamic plantar flexion exercise. Data from this study suggest that previously reported exaggerated exercise pressor reflex in patients with PAD is driven by greater vasoconstriction in nonexercising vascular territories which also results in a redistribution of blood flow to the exercising extremity. However, this rise in femoral blood flow does not fully correct the oxygen deficit due to changes in other mechanisms that require further investigation.

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