Meeting Abstract
P2.125 Monday, Jan. 5 Cardiac, ventilatory and metabolic responses to hypoxia in developing Xenopus laevis PAN, Tien-Chien F.*; BURGGREN, Warren W.; Univ. of North Texas, Denton; Univ. of North Texas, Denton tp0073@unt.edu
Most research on the respiratory development of amphibians has focused on metamorphosis rather than earlier stages when cardio-respiratory reflexes are first appearing. The present study investigated early development of the hypoxic responses under chronic normoxic (150 mmHg) and hypoxic (110 mmHg) conditions. The parameters measured here included gill and lung ventilation, heart rate, stroke volume, cardiac output, mass-specific oxygen consumption and critical PO2. Larvae started gill ventilation at 3 dpf and began air-breathing at 4 dpf. For acute hypoxic responses, larvae developed both hypoxic gill and lung hyperventilation at 5 dpf. Hypoxic tachycardia also developed at 5 dpf and led to increased cardiac output. No differences in stroke volume were observed. Mass-specific O2 consumption decreased following acute hypoxic exposure. Chronic exposure to hypoxia increased both gill and lung ventilation frequency and the hyperventilatory responses to hypoxia, but had no effect on cardiac responses. Hypoxic larvae also exhibited lower O2 consumption than the normoxic group. Our results show that ventilatory and cardiac reflex to acute hypoxia is established as early as 5 dpf. Higher ventilation frequency and enhanced hypoxic responses caused by chronic hypoxia may be due to up-regulation of the O2-sensitive chemoreceptors. The lack of significant changes in cardiac responses between normoxic and hypoxic larvae suggests that O2 diffusion across the respiratory surface is a major limiting factor in O2 uptake. Metabolic responses to hypoxia revealed that early larval Xenopus laevis as O2 conformers.
