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First published online December 10, 2003
Journal of Experimental Biology 207, 269-283 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00744

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-Adrenergic regulation of systemic peripheral resistance and blood flow distribution in the turtle Trachemys scripta during anoxic submergence at 5°C and 21°C

J. A. W. Stecyk^1,*, J. Overgaard², A. P. Farrell¹ and T. Wang²

¹ Department of Biological Sciences, Simon Fraser University, Burnaby, BC, Canada, V5A 1S6
² Department of Zoophysiology, Aarhus University, Building 131, 8000 Aarhus C, Denmark

^* Author for correspondence (e-mail: jastecyk{at}sfu.ca)

Accepted 6 October 2003

Anoxic exposure in the anoxia-tolerant freshwater turtle is attended by substantial decreases in heart rate and blood flows, but systemic blood pressure (P_sys) only decreases marginally due to an increase in systemic peripheral resistance (R_sys). Here, we investigate the role of the -adrenergic system in modulating R_sys during anoxia at 5°C and 21°C in the turtle Trachemys scripta, and also describe how anoxia affects relative systemic blood flow distribution (%_sys) and absolute tissue blood flows. Turtles were instrumented with an arterial cannula for measurement of P_sys and ultrasonic flow probes on major systemic blood vessels for determination of systemic cardiac output (_sys). -Adrenergic tone was assessed from vascular injections of -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 -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 R_sys and functional -adrenergic vasoactivity at both acclimation temperatures. However, while anoxia at 21°C was associated with a high systemic -adrenergic tone, the progressive increase of R_sys at 5°C was not mediated by -adrenergic control. A redistribution of blood flow away from ancillary vascular beds towards more vital circulations occurred with anoxia at both acclimation temperatures. %_sys and absolute blood flow were reduced to the digestive and urogenital tissues (approximately 2- to 15-fold), while %_sys 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 %_sys 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 _sys being directed towards the shell during anoxia at both 5°C and 21°C. -Adrenergic stimulation and blockade during anoxia caused few changes in %_sys and absolute tissue blood flow. However, there was evidence of -adrenergic vasoactivity contributing to blood flow regulation to the liver and shell during anoxic submergence at 5°C.

Key words: red-eared slider, Trachemys scripta, anoxia, temperature, cardiovascular, systemic resistance, cardiac output, blood pressure, -adrenergic control, microsphere, blood flow distribution

This article has been cited by other articles:

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