Trophoblastin, an antiluteolytic protein present in early pregnancy in sheep

Abstract

Trophoblastin, an antiluteolytic component from the embryo, was identified in the ewe by the means of intrauterine injections of homogenates from trophoblasts at 14--16 days pregnancy. Homogenates from embryos and their membranes at 21--23 days pregnancy did not extend the life of the corpus luteum, suggesting that trophoblastin synthesis occurs for only a short period. The trophoblastin was thermolabile (80 degrees C for 30 min) and inactivated by pronase. Treatment of ewes with oCS, hCG, and extracts of 120-day placentae did not affect the time of luteolysis. The protein appears to be insoluble at pH 7 or 8, but to dissolve readily at pH 9.6. After injection of homogenates or extracts from 15--16-day-old trophoblasts, the initial CL were maintained for more than 1 month in most cyclic recipient ewes. Surgical removal of embryos at 21--23 days resulted in luteal maintenace for more than 1 month in over 50% of the operated animals. All the maintained CL were secretory although their average weight was about one-half of that CL of normal pregnancy, suggesting the existence of complementary luteotrophic placental factors. The uteri of most of these pseudopregnant ewes were distended with a clear, sterile fluid.

Interferon-tau, a Type 1 interferon involved in maternal recognition of pregnancy

“…By the late 1970s, it had become clear that there was no common mechanism to explain how CL rescue occurred in different species (4,5). In primates, where the conceptus implants into the uterine wall within a day or two of entering the uterus, a chorionic gonadotrophin (hCG in the case of the human) is secreted by the invading trophoblast, gains access to the maternal blood supply, and provides direct luteotrophic support to the CL.…”

“…Surprisingly, the prospective mother "knows" she is pregnant and her CL is already programmed for extension well before these placentation events are initiated. By 1980, it had become clear that the active factor responsible for CL rescue and extension of the ovarian cycle was a protein produced by the conceptus for a few days prior to when the conceptus attaches to the uterine wall, and only effective if it were introduced into the uterine lumen rather than directly into the ewe's blood stream (4,6). At the University of Florida, my colleagues, Fuller Bazer and Jim Godkin, and I reasoned that the protein factor was probably, therefore, secreted and produced transiently during pregnancy.…”

Peripheral concentrations of a 60-kDa pregnancy serum protein during gestation and after calving and in relationship to embryonic mortality in cattle

“…As in sheep (Martal et al, 1979;Godkin et al, 1982;Imakawa et al, 1987; this signal is an interferon: bTP-1 (bovine trophoblast protein-1) (Helmer etal, 1987;Imakawa et al, 1989;Stewart et al, 1989). bTP-1 interferon is secreted by the conceptus between d 16 and 26 of pregnancy (Bartol et al, 1985) (Beckers et al, 1982).…”

Effect of conceptus removal and intrauterine administration of conceptus tissue on luteal function in the cow

“…Nevertheless, in these species, the mechanism by which the conceptus prevents luteolysis is not yet completely elucidated. In the ewe, PGE2 or other prostanoids (Henderson et al, 1977: Lewis et al, 1978Pratt et al, 1979 ;Marcus, 1981) and a protein of trophoblastic origin (Martal et al, 1979) may be involved in corpus luteum maintenance. In bovines, Northey and French (1980) reported that the embryonic signal(s) may be given between days 15 and 17, but the chronological aspects of the interaction between the conceptus and ovary, as well as its consequences on corpus luteum function and estrous cycle length, were not completely determined.…”