Chemical regulation of cerebral blood flow in turtles

Davies, D. G.

doi:10.1152/ajpregu.1991.260.2.r382

Cited by 6 publications

(10 citation statements)

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“…Similarly, during hypoxia and underwater diving, endotherms redistribute blood flow towards cerebral, myocardial and adrenal vascular beds, while blood flow to visceral organs is reduced by a selective vasoconstriction which, in many cases, is mediated by α-adrenergic control (Johansen, 1964;Elsner et al, 1966;Chalmers et al, 1967;Krasney, 1971;Butler and Jones, 1971;Jones et al, 1979;Zapol et al, 1979). Consistent with these blood flow patterns, blood flow to various visceral organs is reduced during short-term anoxia in anaesthetized turtles, while brain blood flow is largely maintained (Davies, 1989(Davies, , 1991Bickler, 1992;Hylland et al, 1994Hylland et al, , 1996.…”

Section: Sysmentioning

confidence: 85%

“…Changes in systemic blood flow distribution with anoxic exposure A redistribution of blood flow towards oxygen-sensitive tissues such as the brain and heart is critical to survival and is a commonly used survival strategy among vertebrates when exposed to hypoxia (Johansen, 1964;Elsner et al, 1966;Chalmers et al, 1967;Krasney, 1971;Butler and Jones, 1971;Jones et al, 1979;Zapol et al, 1979;Boutilier et al, 1986;Davies, 1989Davies, , 1991Bickler, 1992;Hylland et al, 1994Hylland et al, , 1996Nilsson et al, 1994;Yoshikawa et al, 1995;Söderström et al, 1999). Here, we provide a quantitative description of systemic blood flow distribution during the large depression in cardiac status occurring with anoxic submergence in the anoxia-tolerant freshwater turtle.…”

Section: -Adrenergic Blood Flow Regulation In Anoxic Turtlesmentioning

confidence: 99%

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α-Adrenergic regulation of systemic peripheral resistance and blood flow distribution in the turtleTrachemys scriptaduring anoxic submergence at 5°C and 21°C

Stecyk

Overgaard

Farrell

et al. 2004

Journal of Experimental Biology

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SUMMARYAnoxic exposure in the anoxia-tolerant freshwater turtle is attended by substantial decreases in heart rate and blood flows, but systemic blood pressure (Psys) only decreases marginally due to an increase in systemic peripheral resistance (Rsys). Here,we investigate the role of the α-adrenergic system in modulating Rsys during anoxia at 5°C and 21°C in the turtle Trachemys scripta, and also describe how anoxia affects relative systemic blood flow distribution(%Q̇sys) and absolute tissue blood flows. Turtles were instrumented with an arterial cannula for measurement of Psys and ultrasonic flow probes on major systemic blood vessels for determination of systemic cardiac output(Q̇sys). α-Adrenergic tone was assessed from vascular injections of α-adrenergic agonists and antagonists (phenylephrine and phentolamine, respectively) during normoxia and following either 6 h (21°C) or 12 days (5°C) of anoxic submergence. Coloured microspheres, injected through a left atrial cannula during normoxia and anoxia, as well as after α-adrenergic stimulation and blockade during anoxia at both temperatures, were used to determine relative and absolute tissue blood flows.Anoxia was associated with an increased Rsys and functional α-adrenergic vasoactivity at both acclimation temperatures. However, while anoxia at 21°C was associated with a high systemicα-adrenergic tone, the progressive increase of Rsysat 5°C was not mediated by α-adrenergic control. A redistribution of blood flow away from ancillary vascular beds towards more vital circulations occurred with anoxia at both acclimation temperatures.%Q̇sys and absolute blood flow were reduced to the digestive and urogenital tissues (approximately 2- to 15-fold), while %Q̇sys and absolute blood flows to the heart and brain were maintained at normoxic levels. The importance of liver and muscle glycogen stores in fueling anaerobic metabolism were indicated by increases in%Q̇sys to the muscle at 21°C (1.3-fold) and liver at 5°C (1.7-fold). As well, the crucial importance of the turtle shell as a buffer reserve during anoxic submergence was indicated by 40-50% of Q̇sys being directed towards the shell during anoxia at both 5°C and 21°C. α-Adrenergic stimulation and blockade during anoxia caused few changes in%Q̇sys and absolute tissue blood flow. However, there was evidence of α-adrenergic vasoactivity contributing to blood flow regulation to the liver and shell during anoxic submergence at 5°C.

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Section: Sysmentioning

confidence: 85%

Section: -Adrenergic Blood Flow Regulation In Anoxic Turtlesmentioning

confidence: 99%

α-Adrenergic regulation of systemic peripheral resistance and blood flow distribution in the turtleTrachemys scriptaduring anoxic submergence at 5°C and 21°C

Stecyk

Overgaard

Farrell

et al. 2004

Journal of Experimental Biology

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“…These time-dependent changes have not been observed previously and could ex plain discrepancies between earlier studies on tur tles. Davies (1989Davies ( , 1991, using microspheres, found an approximately threefold increase in brain blood flow after 15-30 min of anoxia (25°C). By contrast, Bickler (1992a), who estimated the average blood flow (from H2 clearance) between 0.…”

Section: Discussionmentioning

confidence: 98%

“…flow after 30 min in anoxia (Davies, 1989(Davies, , 1991, while a 45% increase has been calculated from H2 clearance (Bickler, 1992a). Since systemic blood pressure remains unaltered during anoxia, Davies (1991) suggested that cerebral vasodilation occurs.…”

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confidence: 99%

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Time Course of Anoxia-Induced Increase in Cerebral Blood Flow Rate in Turtles: Evidence for a Role of Adenosine

Hylland

Nilsson

Lutz

1994

J Cereb Blood Flow Metab

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Summary:The exceptional ability of the turtle brain to survive prolonged anoxia makes it a unique model for studying anoxic survival mechanisms. We have used epi illumination microscopy to record blood flow rate in ve nules on the cortical surface of turtles (Trachemys scripta). During anoxia, blood flow rate increased 1.7 times after 45-75 min, whereupon it fell back, reaching preanoxic values after 115 min of anoxia. Topical super fusion with adenosine (50 /-LM) during normoxia caused a 3.8-fold increase in flow rate. Superfusing the brain with Freshwater turtles of the genera Trachemys and Chrysemys possess the exceptional ability among vertebrates to tolerate prolonged anoxia, surviving days of anoxia at room temperature and several months at temperatures close to ooe (Ultsch, 1989).In vertebrates, from mammals (Hansen, 1985; Siesjo, 1992) to fish (Nilsson et aI., 1993), the brain is particularly sensitive to anoxia, rapidly losing ATP levels-the primary cause of neuronal death. To maintain brain ATP levels, turtles utilize two cooperating strategies. An initial enhancement of glycolytic ATP production is followed by deep hy pometabolism (Lutz, 1992).An increased glycolytic rate would probably de mand increased cerebral blood flow and/or an ele vated blood glucose level. Previous studies on tur tles using the microsphere technique have shown an approximately threefold increase in cerebral blood Received January 19, 1994; final revision received March 7, 1994; accepted March 8, 1994.Address correspondence and reprint requests to Dr. P.Hylland at Vertebrate Physiology and Behaviour Unit, Depart ment of Limnology, Norbyvagen 20, S-752 36 Uppsala, Sweden. 877the adenosine receptor blocker aminophylline (250 /-LM)totally inhibited the effects of both adenosine and anoxia, while aminophylline had no effect on normoxic flow rate. None of the treatments affected systemic blood pressure. These results indicate an initial adenosine-mediated in crease in cerebral blood flow rate during anoxia, probably representing an emergency response before deep meta bolic depression sets in.

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Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

Crossley

Burggren

Reiber

et al. 2016

Comprehensive Physiology

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Mass transport can be generally defined as movement of material matter. The circulatory system then is a biological example given its role in the movement in transporting gases, nutrients, wastes, and chemical signals. Comparative physiology has a long history of providing new insights and advancing our understanding of circulatory mass transport across a wide array of circulatory systems. Here we focus on circulatory function of nonmodel species. Invertebrates possess diverse convection systems; that at the most complex generate pressures and perform at a level comparable to vertebrates. Many invertebrates actively modulate cardiovascular function using neuronal, neurohormonal, and skeletal muscle activity. In vertebrates, our understanding of cardiac morphology, cardiomyocyte function, and contractile protein regulation by Ca2+ highlights a high degree of conservation, but differences between species exist and are coupled to variable environments and body temperatures. Key regulators of vertebrate cardiac function and systemic blood pressure include the autonomic nervous system, hormones, and ventricular filling. Further chemical factors regulating cardiovascular function include adenosine, natriuretic peptides, arginine vasotocin, endothelin 1, bradykinin, histamine, nitric oxide, and hydrogen sulfide, to name but a few. Diverse vascular morphologies and the regulation of blood flow in the coronary and cerebral circulations are also apparent in nonmammalian species. Dynamic adjustments of cardiovascular function are associated with exercise on land, flying at high altitude, prolonged dives by marine mammals, and unique morphology, such as the giraffe. Future studies should address limits of gas exchange and convective transport, the evolution of high arterial pressure across diverse taxa, and the importance of the cardiovascular system adaptations to extreme environments. © 2017 American Physiological Society. Compr Physiol 7:17-66, 2017.

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Chemical regulation of cerebral blood flow in turtles

Cited by 6 publications

References 0 publications

α-Adrenergic regulation of systemic peripheral resistance and blood flow distribution in the turtleTrachemys scriptaduring anoxic submergence at 5°C and 21°C

α-Adrenergic regulation of systemic peripheral resistance and blood flow distribution in the turtleTrachemys scriptaduring anoxic submergence at 5°C and 21°C

Time Course of Anoxia-Induced Increase in Cerebral Blood Flow Rate in Turtles: Evidence for a Role of Adenosine

Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

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