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| − | {{review}}
| + | <big><center>[[Female Reproductive Tract -The Ovary - Anatomy & Physiology|'''BACK TO THE OVARY''']]</center></big> |
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| − | == The Luteolytic Mechanism ==
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| − | * Prostaglandin F2α (PGF2α)
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| − | * PGF2α from the uterus is transported to the ipsilateral ovary through a vascular counter-current exchange mechanism.
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| − | * This involves two closely associated blood vessels in which blood from one vessel flows in the opposite direction to that of the adjacent vessel.
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| − | * Low molecular weight substances in high concentrations in one vessel cross over into the adjacent vessel, where they are low in concentration.
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| − | * The ovarian artery lies in closs association with the utero-ovarian vein.
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| − | * By counter-current exchange, PGF2α is transferred across the wall of the uterine vein into the ovarian artery by passive diffusion.
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| − | * This ensures a high proportion of PGF2α produced by the uterine glands will be transported directly to the ovary and corpus luteum without dilution in the systemic circulation.
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| − | * This is an important mechanism, because much PGF2α is denatured during one pass through the circulatory system. This is about a 90% loss in the ewe and cow.
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| − | == Luteolysis in Ruminants ==
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| − | * The ruminant corpus luteum secretes large amounts of oxytocin as well as progesterone.
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| − | * In the late luteal phase, oxytocin receptors develop on the uterine endometrium.
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| − | * Binding of oxytocin to the receptors stimulates the pulsatile release of PGF2α.
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| − | * PGF2α secretion by the endometrium is almost non-existant during the first half of the luteal phase.
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| − | * During the late luteal phase, pulses of PGF2α secretion increase in frequency and amplitude as the end of the luteal phase approaches.
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| − | * A critical number of PGF2α pulses are required within a given time span to induce complete luteolysis.
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| − | ** In the ewe, this is ~5 pulses in 24 hours.
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| − | * During the first half of the cycle, progesterone prevents the secretion of PGF2α by blocking the formation of oxytocin receptors on the uterus.
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| − | * Oxytocin and PGF2α stimulate each other in a positive feedback manner.
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| − | * The greater the number of endometrial oxytocin receptors, the greater the ability of oxytocin to stimulate PGF2α synthesis.
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| − | [[Category:Female Reproduction]]
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| − | [[Category:Bullet Points]]
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