Avian embryonic thermoregulation: role of Q 10 in interpretation of endothermic reactions

Abstract

1. Incubated chicken eggs (D14 to D21) were placed separately in transparent acrylic glass chambers which were immersed in a 37.5°C water bath for 3 h. The chambers were then moved for 3 h to another water bath controlled at 34.5°C. Oxygen consumption and temperature of the allantoic fluid ( T af) were measured at 5-min intervals for the whole experiment using an oxygen analyzer and CrNi–Ni-thermocouples, respectively. Heat production (HP) was calculated, using an assumed RQ of 0.72. 2. At 37.5°C the relationship between HP and embryonic age follows a sigmoid curve. Between D18 (HP 7.25 J g −1 h; 2.01 W kg −1) and D19 (HP 7.21 J g −1 h −1; 2.00 W kg −1) this function had a plateau phase with a duration of about 24 h. 3. During the cooling process, HP decreased continuously and the relationship between T a and HP could be described by an exponential function. From the results, it was possible to calculate the relationships between T af, as a measure of body core temperature, and Q 10; the lower the T af the higher the Q 10. 4. Because the actual measured HP is the result of the negative effect of Q 10 on HP and the stimulating influence of the CNS-generated HP, a Q 10 of more than 2.0 demonstrates the absence of endothermy. Chicken embryos aged between 14 and 21 d have a Q 10 of less than 2.0 at body temperatures ( T af) between 34 and 30°C. It is postulated that in chicken embryos of this age endothermic reactions may occur. 5. The Q 10-method is suitable for investigating the prenatal development of endothermic reactions in avian embryos.