RESPIRATORY REGULATION IN AMPHIBIAN DEVELOPMENT

¹ Zoology Department, Duke University, Durham, North Carolina

1. The respiratory rate of Rana pipiens control embryos is an increasing function of developmental stage, with an acceleratory change at the onset of the formation of the neural folds.

2. At any stage of development, the respiratory rate of Rana pipiens embryos is elevated by the presence of 2,4-dinitrophenol (DNP). The degree of stimulation obtainable ranges from about 400% of the control rate at the beginning of development to about 150% of the control rate at the gill-circulation stage.

3. The respiratory rate of Rana pipiens x Rana sylvatica embryos is an increasing function of time, but the rate of increase is very much lower than that of the respiratory rate of Rana pipiens controls.

4. At any stage, the respiratory rate of hybrid embryos is elevated by DNP. The degree of stimulation obtainable ranges from about 400% at the beginning of development to about 300% at 118 hours after fertilization (18° C.).

5. The respiratory activity of homogenates of Rana pipiens embryos at any stage is not altered by the addition of DNP.

6. The relevance of these findings to the question of embryonic respiratory control is discussed. It is concluded that, within the capacity to respire, respiration is governed by energy expenditure, and that the capacity to respire increases with age as the result of intracellular changes facilitating contact between respiratory enzymes and substrates.