Fig. 3. Changes in the activity of antioxidant enzymes expressed as units mg^–1 protein in lung tissue of frogs at developmental stages 30–46. Lungs from 10–30 animals were pooled for each sample. Values are means, means ± range or means ± S.E.M., depending on the number of measurements per stage (N=1 for stages 30, 35, 38; N=2 for stages 32, 34, 42; N=3 for all other stages). Catalase activity (A) remained unchanged for stages 30–40 (y=0.8272x+43.811; r²=0.0997; N=10) and thereafter increased exponentially (y=4.6563e^0.0705x; r²=0.7059; N=7; P<0.01). SOD activity (B) remained unchanged over the entire developmental period (y=0.0175x+5.7001; r²=0.0137; N=17). GPx activity (C) remained unchanged over the entire developmental period (y=5x10^–5x+0.0255; r²=0.0011, N=17).