Synthetic Capabilities of the Preimplantation Conceptus and Maternal Responses to Pregnancy

Heap, R. B.; Staples, Linton; Flint, A. P. F.; Walker, Felicity M. Maule; Allen, William R.

doi:10.1007/978-3-642-68800-3_28

Cited by 1 publication

(2 citation statements)

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“…Others, such as the sheep, human and higher primates, rely initially on ovarian progesterone but the supply is soon supplemented by progesterone secreted by the developing placenta to the extent that, by the end of the first trimester, the mother can withstand bilateral ovariectomy without losing the pregnancy. Nonetheless, despite this rapid take‐over by placental progesterone the ovarian CL remains present and continues to secrete throughout gestation (Heap et al. 1983).…”

Section: The Sources Of Progesterone In Equine Pregnancymentioning

confidence: 99%

“…Others, such as the sheep, human and higher primates, rely initially on ovarian progesterone but the supply is soon Reprod Dom Anim 36, 121±131 (2001) Ó 2001 supplemented by progesterone secreted by the developing placenta to the extent that, by the end of the ®rst trimester, the mother can withstand bilateral ovariectomy without losing the pregnancy. Nonetheless, despite this rapid take-over by placental progesterone the ovarian CL remains present and continues to secrete throughout gestation (Heap et al 1983). The African elephant, Loxodonta Africanus, has its own strange variation on the theme for progestational activity during pregnancy in that multiple (2±5) large and healthylooking CLs appear in the ovary ipsilateral to the uterine horn containing the singleton conceptus from the very earliest stages of gestation where they secrete minimal quantities of native progesterone but appreciable amounts of two 5 pregnane derivatives of progesterone, 5aDHP and 5a-pregnane-3a-ol-20-one (Hodges et al 1997).…”

Section: The Sources Of Progesterone In Equine Pregnancymentioning

confidence: 99%

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Luteal Deficiency and Embryo Mortality in the Mare

Allen

2001

Reprod Domest Anim

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Four separate components combine to produce the progesterone and biologically active 5 alpha-reduced pregnanes needed to maintain pregnancy in the mare. The primary corpus luteum (CL) is prolonged beyond its cyclical lifespan by the down-regulation of endometrial oxytocin receptors to prevent activation of the luteolytic pathway and its waning progesterone production is supplemented from day 40 of gestation by the formation of a series of accessory CL which develop in the maternal ovaries as a result of the gonadotrophic actions of pituitary FSH and the equine chorionic gonadotrophin (eCG). From around day 100 the allantochorion secretes progesterone and progestagens directly to the endometrium and underlying myometrium and, in the last month of gestation, the enlarging foetal adrenal gland secretes appreciable quantities of pregnenelone which is also utilized by the placenta to synthesize progestagens. Between 10 and 15% of mares undergo foetal death and abortion at some time in gestation and the majority of these losses occur during the first 40 days of gestation when the primary CL is the sole source of progesterone. Yet, all the available evidence suggests that untoward luteolysis is not common in this period and the losses that do occur have other underlying causes. Beyond day 40 the secondary CL receive powerful luteotrophic support from eCG and from day 80-100 until term the supply organ (placenta) and target tissues (endometrium and myometrium) are in direct contact with each other over their entire surface. In the face of this interlocking and failsafe system for progestagen production throughout pregnancy, and despite a paucity of evidence that a deficiency of progesterone production is a cause of pregnancy loss in the mare, it is surprising, and worrying, that annually many thousands of pregnant mares throughout the world are given exogenous progestagen therapy during part or all of their gestation as a form of preventative insurance against the possibility of pregnancy failure. Basic investigative research is required urgently to validate or debunk the practice.

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Section: The Sources Of Progesterone In Equine Pregnancymentioning

confidence: 99%

Section: The Sources Of Progesterone In Equine Pregnancymentioning

confidence: 99%