Comparative studies of the maternal recognition of pregnancy

Abstract

SummaryOf primary importance for the establishment of pregnancy is the maintenance or prolongation of corpus luteal function. In large domestic animals this is achieved by a blastocyst‐derived signal which disarms the uterine luteolytic mechanism some time before there is any structural association between embryonic and maternal tissues. This is not the case in all mammals because, in certain instances, maternal recognition of pregnancy, as defined by luteal response in terms of maintained or prolonged function, may correspond with the onset of nidation and even post date the time of attachment and implantation. Evidence for the importance of blastocyst‐derived signals and their intensity has been examined but the hypothesis requires further testing to elucidate the relationship between stimulus (signal) and response (luteal function). Studies of the mechanisms by which progesterone action can be blocked in early pregnancy currently focus on target cell epithelia in the uterus and the nature of surface antigens associated with the onset of the implantation process. To date, proof is lacking for a uterus‐specific growth factor with unique functions which forms an essential component of histotrophe; but there is substantial evidence that polypeptide growth factors are detectable at significant concentrations in the uterus. The development of specific peptide antagonists should help to reveal the functions of polypeptide mitogens in uterine physiology and their role in the complex cellular signalling and recognition that occurs between embryo and mother in the early stages of gestation (Brigstocket al1989).