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Ontogeny of ventilatory regulation in the bullfrog Rana catesbeiana
Abstract
The ontogeny of ventilatory control was studied in developing bullfrogs (Rana catesbeiana) by measuring gill and lung ventilation frequency (f$\sb{\rm G}$ and f$\sb{\rm L},$ respectively) and blood parameters after exposure to variations in environmental PO$\sb2$ and PCO$\sb2.$ Early in larval development (Taylor-Kollros Stages V-XV), both f$\sb{\rm G}$ and f$\sb{\rm L}$ increased during exposure to aquatic hypoxia, with little sensitivity to water PCO$\sb2.$ The PO$\sb2$ of lung gas also affected f$\sb{\rm G}$ and f$\sb{\rm L}.$ Gas hypoxia caused an increase in f$\sb{\rm L}.$ Gas hyperoxia caused a reduction in f$\sb{\rm L}$ and f$\sb{\rm G}.$ Hypercapnic gas exposure did not significantly affect f$\sb{\rm G}$ or f$\sb{\rm L}.$ St. V-XV larvae showed a marked respiratory acidosis (decrease in blood pH and increase in blood PCO$\sb2)$ upon exposure to hypercapnic water, with no change in blood bicarbonate or O$\sb2$ content. In larvae beginning metamorphosis (St. XVI-XIX), hypoxic stimulation of f$\sb{\rm L}$ persisted, and sensitivity to CO$\sb2$ dramatically increased. Hypercapnic exposure caused increases in f$\sb{\rm L}$ and depressed f$\sb{\rm G}.$ Despite increased pulmonary ventilatory sensitivity to CO$\sb2$ in St. XVI-XIX larvae, a respiratory acidosis comparable to St. V-XV larvae was measured after exposure to hypercapnic water. No adjustments in blood bicarbonate or O$\sb2$ content were seen in response to aquatic gas composition changes. In post-metamorphic froglets (St. XXV) f$\sb{\rm L}$ was stimulated by both gas hypoxia and hypercapnia. Blood pH and PCO$\sb2$ in froglets did not change significantly after hypercapnic exposure. Blood PCO$\sb2$ was significantly reduced during hypoxic gas exposure as a result of hyperventilation, with no significant change in blood pH. Blood O$\sb2$ content was significantly reduced by exposure to gas hypoxia and hypercapnia. These studies provide evidence that there are multiple sites of oxygen chemosensitivity in bullfrogs. Additionally, the regulatory mechanism by which O$\sb2$ and CO$\sb2$ influence gill and lung ventilation may be an interactive one.
Subject Area
Zoology|Ecology|Physiology
Recommended Citation
Infantino, Robert Louis, "Ontogeny of ventilatory regulation in the bullfrog Rana catesbeiana" (1992). Doctoral Dissertations Available from Proquest. AAI9219447.
https://scholarworks.umass.edu/dissertations/AAI9219447