Changes in respiratory functions during metamorphosis of the bullfrog, Rana catesbeiana

Blood pH and P co 2, were measured in tadpoles of R. catesheiana from stages XVIII through XXV and in adults. All animals were kept at 23°C for at least 2 weeks before samples were taken for analysis. Bicarbonate concentrations of the blood were calculated using the Henderson-Hasselbalch equation with appropriate corrections for constants. Carbon dioxide tension increased from about 5 torr at stage XX to about 15 torr at stage XXIII with no significant increase thereafter. Bicarbonate concentration increased progressively from a low of 8.4 mM/L at stage XX to a high of 27.6 mM/L in adults. In vivo pH of cardiac blood decreased from 7.82 in stage XX tadpoles to about 7.65 at stage XXI and thereafter remained essentially unchanged even in the adult (pH = 7.68). The critical phase of respiratory metamorphosis occurs during stages XXI and XXII and takes place in about 5 days.