Maternal recognition in different species

• Maternal recognition of pregnancy

  1. Successful pregnancy depends on the prolongation of the life-span of the CL

  2. Embryo sends a signal - secretes factors - estrogens or proteins that act locally not systemically

  3. The signals either: 1. Prevent the secretion of PGF2 2. Have direct luteotropic effect
• Sows

  1. Effect of estrone is local and not systemic

  2. Embryos must be present in both uterine horns

  3. Absence of embryos in one horn - no estrone - PGF2 released into the blood from that horn

  4. Luteolysis of CL in both ovaries
• Ruminants

  1. Trophoblast cells produce interferon-τ (IFN-τ) - previously known as interferon and trophoblastic protein 1

  2. Appears in the uterus between days 12-23 after ovulation

  3. IFN-τ inhibits the expression of receptors for oxytocin and estrogen in luminal and superficial glandular epithelial cells

  4. The reduction in estradiol receptor expression further suppresses oxytocin receptor expression

  5. Progesterone also blocks estrogen and oxytocin receptor expression in deep glandular epithelial cells

  6. Combination of IFN-τ & progesterone prevents oxytocin-induced uterine secretion of PGF2α
• Ruminants

  1. Some ruminants also secrete another protein which blocks the effects of PGF2α on large luteal cells

  2. Therefore, the ruminant conceptus prolongs the life span of the CL by (i) preventing PGF2α secretion and (ii) preventing the actions of PGF2α
• Rodents

  1. Biphasic release of PRL as a result of coitus - PRL is a luteotropic signal

  2. Release continues for 10 -12 days in pseudopregnant animals - then decreases

  3. In pregnant rats, when pituitary PRL decreases - placenta secretes placental lactogen which rescues the CL

  4. Also ↑ androgen production → ↑ estrogen production

  5. PRL & estrogen → ↑ luteal progesterone production and cellular hypertrophy
• Equids


  1. Embryos still in an acellular capsule - in contact with only a small amount of area

  2. Migration of embryo to distribute proteins

  3. 12-14 times per day, 5-20 minutes per area

  4. The proteins alters the ratio of PGE2 to PGF2α in uterine veins - PGE2 luteotropic - continued luteal function until day 35

  5. At day 28 binucleate cells form endometrial cups during placenta formation - secretes equine chorionic gonadotropin (eCG) or pregnant mare serum gonadotropin (PMSG)

  6. eCG maintains primary CL - induces secondary CL - ↑ progesterone

  7. Endometrial cups regress by 130th day of gestation - placenta handles progesterone secretion

  
• Carnivores


  No need for antiluteolytic mechanisms because of the long life span of the CL
• Humans

  Trophoblast cells secrete hCG from 8 - 10 days gestation - rescues the CL - secretion declines after the first trimester