Abstract:
The processes leading to implantation and the establishment of pregnancyinvolve hormonal and non-hormonal agents that offer opportunities as targetsfor contraception. Hormonal agents include progesterone, luteolytic factors(prostaglandin F<emph type="8">2α ) and embryonic signals(chorionic gonadotrophin, oestradiol-17β, interferon-&tgr; ) responsiblefor maintaining the corpus luteum. Non-hormonal agents include surfaceantigens (attachment and adhesion molecules), vasoactive agents,tissue-remodelling enzymes (matrix metalloproteinases) and inhibitors (TIMPs),growth factors (epidermal growth factor and insulin-like growth factorfamilies) and cytokines (such as leukaemia inhibitory factor,colony-stimulating factor-1, interleukin-1 (IL-1) and IL-6) associated withthe pre-attachment period and the apposition, adhesion and invasion of theblastocyst. This review describes some of the hormonal and non-hormonal agentspresent at the time of implantation that may be exploited as targets forcontraception in feral species. Particular attention is paid to the mouse asan experimental model and potential target species. The considerable speciesdifferences which exist in the modes of implantation and placentation and theway in which the female ‘recognizes’ the presence of a viableconceptus offer a means of conferring species specificity on potentialcontraceptive targets for feral species.