Activity trends of adenylate and guanylate cyclases and cAMP and cGMP levels during the first embryonic stages of Bufo bufo.

1. During the first stages of embryonic development of Bufo bufo, the levels of cAMP and cGMP showed interesting opposite trends analogous to the trends of their respective enzymes. 2. In the late segmentation, the high increase of guanylate cyclase specific activity and the corresponding rise of embryonic level of cGMP, could indicate the involvement of this nucleotide in cellular proliferation. 3. During the following stage of the gastrulation, the increase of adenylate cyclase specific activity, coupled to the loss of guanylate cyclase specific activity, could suggest the importance of cAMP in the phenomena of differentiation induction. 4. Furthermore, the cytochemical investigation of adenylate and guanylate cyclase localization seems to confirm the prominent role of cAMP during the differentiation phases.