Respiratory responses to short term hypoxia in the snapping turtle, Chelydra serpentina

Among vertebrates, turtles are able to tolerate exceptionally low oxygen te nsions. We have investigated the compensatory mechanisms that regulate resp iration and blood oxygen transport in snapping turtles during short exposur e to hypoxia. Snapping turtles started to hyperventilate when oxygen levels dropped below 10% O-2. Total ventilation increased 1.75-fold, essentially related to an increase in respiration frequency. During normoxia, respirati on occurred in bouts of four to five breaths, whereas at 5% O-2, the ventil ation pattern was more regular with breathing bouts consisting of a single breath. The increase in the heart rate between breaths during hypoxia sugge sts that a high pulmonary blood flow may be maintained during non-ventilato ry periods to improve arterial blood oxygenation. After 4 days of hypoxia a t 5% O-2, hematocrit, hemoglobin concentration and multiplicity and intraer ythrocytic organic phosphate concentration remained unaltered. Accordingly, oxygen binding curves at constant P-CO2 showed no changes in oxygen affini ty and cooperativity. However, blood pH increased significantly from 7.50 /- 0.05 under normoxia to 7.72 +/- 0.03 under hypoxia. The respiratory alka losis will produce a pronounced in vivo left-shift of the blood oxygen diss ociation curve due to the large Bohr effect and this is shown to be critica l for arterial oxygen saturation. (C) 2000 Elsevier Science Inc. All rights reserved.