AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 2 382-R384, Copyright © 1991 by American Physiological Society
Chemical regulation of cerebral blood flow in turtles
D. G. Davies
Department of Physiology, Texas Tech University Health Sciences Center, Lubbock 79430.
This study was performed to test the effect of the chemical composition of
the blood on cerebral blood flow (CBF) regulation in turtles. The CBF
response to increases in arterial PCO2 (PaCO2) (hypercapnia) was measured
during normoxia and anoxia in anesthetized freshwater turtles Pseudemys
scripta. The radioactive-microsphere technique was used to measure CBF. CBF
increased with increases in PaCO2. The sensitivity of the CBF response to
hypercapnia (delta CBF/delta PaCO2) was 0.68 ml.min-1.100 g-1. Torr-1
during normoxia. delta CBF/delta PaCO2 increased to 3.44 ml.min-1.100 g-1.
Torr-1 during anoxia. The increases in CBF occurred at constant mean
arterial blood pressure, which indicates that cerebral vascular resistance
decreased. The increased CBF response during asphyxia (hypercapnia-anoxia)
could be beneficial for survival during prolonged dives by increasing
glucose delivery for brain anaerobic metabolism. In addition, increased CBF
could aid in regulating brain acid-base composition by controlling
extracellular fluid PCO2.
