ACE expression and enzymatic activity during the first few days of chicken embryo development. (A) Expression and semiquantification of ACE mRNA by RT-PCR in whole embryo including the yolk sac. The amount of ACE mRNA from 0 to 56 hours of development (HH0 to HH16) was normalized according to cGAPDH mRNA levels. (B) Levels of ACE, AGT, renin, and cAT mRNA, as determined by RT-PCR (35 cycles) in the yolk sac at 24 hours of development (stage HH6). (C) ACE activity in embryos with their yolk sacs from 18 to 56 hours of development (HH4 to HH16), evaluated by hydrolysis of the highly specific synthetic substrate HHL (see “Material and methods”). Each point represents ACE activity in a pool of n = 30 (stage HH4) to n = 3 (stage HH16) embryos (duplicate values).