Critical events surrounding the maternal recognition of pregnancy in mares

Summary An experiment was undertaken to determine whether the equine conceptus inhibits production of prostaglandin F 2α in the pregnant mare. Endometrial tissue was obtained from two normally cycling mares and conceptus membranes were obtained from a further two mares which were pregnant. Endometrial tissue was cultured alone and with conceptus membranes and the prostaglandin F 2α concentrations measured in the incubation medium over a 24 h period. With endometrium alone, prostaglandin F 2α concentrations increased slowly for the first 9 h of incubation but then began to rise sharply. When the conceptus membranes were added, the prostaglandin F 2α production rate was initially comparable to that of endometrium alone but the sharp increase seen after 9 h was large attenuated. By 18 to 24 h, the prostaglandin F 2α concentration in the endometrium plus conceptus membranes was 63 per cent less than for endometrium alone. The results corroborate previous studies that conceptus membranes can inhibit prostaglandin F 2α synthesis.