AJP - Regulatory, Integrative and Comparative Physiology, Vol 262, Issue 3 538-R541, Copyright © 1992 by American Physiological Society
Effects of temperature and anoxia on regional cerebral blood flow in turtles
P. E. Bickler
Department of Anesthesia, University of California, San Francisco 94143-0542.
Regional cerebral blood flow (CBF) was measured in isoflurane-anesthetized
turtles (Pseudemys scripta) by the hydrogen clearance method. Teflon-coated
platinum electrodes (25 microns) were implanted in the olfactory bulbs,
midcerebral cortex and cerebellum in eight adult turtles. The electrodes
were voltage clamped at +0.30 V relative to a Ag-AgCl electrode implanted
in the dorsal neck muscles. Washout kinetics of H2 gas administered via
controlled ventilation was used to calculate local blood flow for
electrodes exhibiting monoexponential washout kinetics of hydrogen (92 of
104 determinations). Data were obtained in animals with body temperatures
of 15, 25, and 35 degrees C under normocapnic conditions during ventilation
with 21% O2 and during ventilation with 100% N2. During normoxia, mean
blood flows were 1.9 +/- 0.8, 5.0 +/- 1.9, and 6.1 +/- 1.3 (+/- SD) ml.100
g-1.min-1 at 15, 25, and 35 degrees C, respectively. There were no
differences between CBF values in the different brain regions. During 1-3 h
of anoxia, CBF was 3.0 +/- 2.1, 7.0 +/- 3.7, and 6.6 +/- 2.9 ml.100
g-1.min-1 at 15, 25, and 35 degrees C, respectively (normoxia-anoxia
difference not statistically different). Hypercarbia (ventilation with
10-20% CO2 in air or N2), or the transition from anoxia to normoxia,
increased CBF up to 80% at each of these temperatures. Maintenance of CBF
during anoxia likely contributes to the anoxia tolerance of the turtle
brain.
