Platelet-activating factor antagonists and implantation in rabbits

In an initial experiment, rabbits were injected i.v. with a platelet-activating factor (PAF) antagonist CV-3988 twice a day on days 5 and 6 of pregnancy. Some inhibition of implantation was observed. This effect could not be reproduced in subsequent experiments at the same or at larger or smaller doses. The non-metabolized analogue of PAF, N-carbamyl-PAF (C-PAF) had an inhibitory effect on implantation only when given at toxic concentrations. When CV-3988 and C-PAF were given together on days 5 and 6, there was no effect on implantation. None of the other PAF antagonists tested - BN52021, SR163,441, WEB2086 or TCV-309 - at various doses could inhibit implantation when given on the same days of pregnancy. TCV-309, at 0.1 mg kg^-1 i.v. given on days 2-4 of pregnancy, was also ineffective. These results provide no clear support for a role of PAF in implantation in rabbits.