The effect of graded hypoxia on the metabolic rate and buccal activity of a lungless salamander (Desmognathus fuscus)

The hypothesis that the lungless salamander Desmognathus fuscus responds ac tively to hypoxia was tested. Patterns of buccal movements [apneic period d uration, the duration (min h(-1)) of buccal pumping and buccal pumping freq uency], heart rate and metabolic rate (rates of oxygen uptake and carbon di oxide output) were determined during a control period (21% oxygen), a hypox ic period (2, 5, 6.5, 8 or 10% oxygen) and a recovery period (21% oxygen), Hypoxic salamanders maintained their rate of oxygen uptake at control level s until a critical oxygen level between 10 and 8% oxygen was reached. The r ate of carbon dioxide output remained constant across all oxygen levels, ex cept for a significant increase during exposure to 5% oxygen. The buccal ac tivity of lungless salamanders was responsive to environmental hypoxia, wit h a significant stimulation during exposure to 6.5% and 5% oxygen. Buccal p umping frequency was inhibited at 2% oxygen. Heart rate was stimulated at a ll hypoxic levels except 2% O-2, During recovery, metabolic rate and heart rate returned to control levels within 20 min in after all hypoxic exposure s. The durations of apneic periods increased significantly compared with th e hypoxic value during recovery from exposure to 10%, 6.5% and 5% oxygen. O verall, the animals responded actively to hypoxia by increasing the duratio n of buccal activity as oxygen levels decreased. The ability of these chang es to facilitate oxygen uptake is not known. However, the response of the d usky salamander to low levels of oxygen is analogous to the hypoxic ventila tory response observed in lunged vertebrates.