Role of histamine and cyclic nucleotides in implantation in the rabbit

The effect of histamine on cAMP and cGMP levels in day 6 (144 h post coitum) rabbit blastocysts was determined. Histamine at 200 microM and 1000 microM concentrations stimulated the increased formation of cAMP in vitro, whereas stimulation of cGMP occurred only in the presence of 1000 microM histamine. Furthermore, intrauterine injection of RMI-12330 A (50 microgram or 500 microgram/uterine horn), an inhibitor of adenylyl cyclases, on day 5 of pregnancy interrupted embryo development and implantation of the embryo. The drug was also effective in reducing the cAMP level in the endometrial cells in vitro. A relationship between histamine and cyclic nucleotide changes in embryo development and implantation is suggested.