Cyclic AMP and cyclic GMP in the implantation site of the rat

Endometrial differentiation of the implantation site (IS) is regulated by hormonal and local influences (egg). To better understand the possible participation of cyclic nucleotides in this process, we measured cAMP and cGMP by RIA in IS of the rat on day 6 of pregnancy. IS showed an increase of both nucleotides (3.54 and 0.57 pmoles/mg DNA) when compared with the remaining endometrium (NIS) (2.70 and 0.30). The cAMP/cGMP ratio did not change significantly. We also found an increase in the proteins/mg DNA ratio (12.04 in IS vs 10.63 in NIS) and in the hydration of IS. Our hypothesis is that together these two nucleotides function as a monodirectional system in which they act cooperatively as positive effectors of different sequential steps in the overall process of implantation.