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Normally the concentration of PGF<sub>2α</sub> in arterial blood is relatively low due to extensive metabolism by PGF<sub>2α</sub>-dehydrogenase in especially the lungs). These levels are below the threshold required to cause luteolysis as PGF<sub>2α</sub> production in early gestation is low.
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Normally the concentration of PGF<sub>2α</sub> in arterial blood is relatively low due to extensive metabolism by PGF<sub>2α</sub>-dehydrogenase (in especially the lungs). These levels are below the threshold required to cause luteolysis as PGF<sub>2α</sub> production in early gestation is low.
 
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The  [[Ovary_-_Anatomy_%26_Physiology#Arterial_Supply|ovarian artery]] is wrapped around the uterine vein. This creates a countercurrent mechanism by which the lipid soluable prostaglandins are able to diffuse from the uterine vein into the [[Ovary_-_Anatomy_%26_Physiology#Arterial_Supply|ovarian artery]]. During the latter stages of the [[Oestrous_Cycle_-_Anatomy_%26_Physiology|luteal phase]] as PGF<sub>2α</sub> production increases luteolysis will occur as PGF<sub>2α</sub> Is able to reach its target in the ovary before being metabolized in systemic circulation.
 
The  [[Ovary_-_Anatomy_%26_Physiology#Arterial_Supply|ovarian artery]] is wrapped around the uterine vein. This creates a countercurrent mechanism by which the lipid soluable prostaglandins are able to diffuse from the uterine vein into the [[Ovary_-_Anatomy_%26_Physiology#Arterial_Supply|ovarian artery]]. During the latter stages of the [[Oestrous_Cycle_-_Anatomy_%26_Physiology|luteal phase]] as PGF<sub>2α</sub> production increases luteolysis will occur as PGF<sub>2α</sub> Is able to reach its target in the ovary before being metabolized in systemic circulation.
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Horses and pigs do not poses this countercurrent mechanism. In these spp. the [PGF<sub>2α</sub>-dehydrogenase] in systemic circulation is much lower in order to induce luteolysis when Prostaglandin concentration rises.
    
===Prostaglandin (PGE<sub>2</sub>)===
 
===Prostaglandin (PGE<sub>2</sub>)===